Diagnosis of Skull Base Osteomyelitis

Published Online:https://doi.org/10.1148/rg.2021200046

Abstract

Skull base osteomyelitis (SBO) is an infection of the temporal, sphenoid, or occipital bone that can be a challenge to diagnose because of its nonspecific symptoms, long clinical course, and radiologic findings that mimic those of other entities. The authors review this unusual infection on the basis of six proven cases. The diagnosis of SBO should be made according to four points: a high index of clinical suspicion, radiologic evidence of infection, repeated biopsies that are negative for malignancy, and positive results of microbiologic tests. SBO typically manifests clinically in patients with diabetes and recurrent otitis externa; the infection usually extends inferiorly to the compact bone of the infratemporal fossa, affecting the lower cranial nerve foramina. Several image-based techniques should be used to diagnose SBO. CT is the best option for evaluating bone erosion and demineralization, MRI can help delineate the anatomic location and extent of disease, and nuclear imaging is useful for confirming bone infection with high sensitivity. However, the standard diagnostic procedure for SBO is for patients to undergo repeated biopsies to rule out malignancy, with histopathologic signs of infection and detection of microorganisms in the biopsied bone or soft tissue indicating SBO. The ability to diagnose SBO can be increased by identifying patients at risk, recognizing the most important causes and routes of infection, describing the main radiologic findings, and always considering the differential diagnosis.

©RSNA, 2021

SA-CME LEARNING OBJECTIVES

After completing this journal-based SA-CME activity, participants will be able to:

  • ■ Identify the patients most typically affected by SBO.

  • ■ Describe the main route of infection in SBO and list the most common pathogens related to this type of infection.

  • ■ Discuss radiologic findings related to SBO and discuss its differential diagnosis with other entities such as nasopharyngeal carcinoma.

Introduction

Teaching Point Skull base osteomyelitis (SBO) is an infection of the temporal, sphenoid, or occipital bones that is typically caused by a complication of improperly treated otogenic or sinonasal infection in elderly patients with diabetes or immunocompromised patients
. However, other diseases can cause the development of SBO without a preceding sinonasal or otogenic infection (14).

SBO is a rare life-threatening disease with nonspecific symptoms. Several diseases can mimic SBO at imaging, and SBO can be misinterpreted as a malignancy. The diagnosis of SBO is therefore often delayed, and a high index of clinical suspicion is required (5).

In this review, we describe the anatomy of the skull base, patient symptoms at clinical presentation, causes and routes of infection, imaging findings, complications, differential diagnosis, and treatment of SBO. The imaging findings will be explained with six sample cases from our hospital between 2015 and 2020.

Skull Base Anatomy

The skull base has a complex anatomy formed by the frontal, temporal, occipital, ethmoid, and sphenoid bones. From an endocranial view, the skull base can be subdivided into three regions: anterior, central, and posterior (Fig 1). The anterior to central skull base regions are separated by the posterior margin of the lesser wing of the sphenoid bone, the anterior clinoid processes, the tuberculum sellae, and the anterior margin of the greater wing of the sphenoid bone. The border between the central and posterior skull base regions is the superior margin of the petrous part of the temporal bone and the dorsum sellae (6).

Endocranial skull base anatomy and subdivisions.

Figure 1. Endocranial skull base anatomy and subdivisions.

The skull base has numerous foramina and channels that are crossed by important nerves and vascular structures. Disorders in this bone can result in damage to these structures and can cause specific symptoms, depending on the lesion’s situation (Figs 2, 3) (6).

Endocranial skull base view of the foramina and cranial nerves.

Figure 2. Endocranial skull base view of the foramina and cranial nerves.

Exocranial skull base view of the foramina and cranial nerves. Dashed                     lines indicate that the mastoid and tympanic canaliculus are intraosseous and                     not visible from this perspective.

Figure 3. Exocranial skull base view of the foramina and cranial nerves. Dashed lines indicate that the mastoid and tympanic canaliculus are intraosseous and not visible from this perspective.

The anatomy of the central skull base is complicated owing to the confluence of numerous essential structures. This region contains cavernous sinuses that are crossed by both internal carotid arteries and the oculomotor (III), trochlear (IV), ophthalmic, and maxillary divisions of the trigeminal (V1 and V2) and abducens (VI) nerves. The cranial nerve V2 leaves the cavernous sinus, traveling toward the foramen rotundum and arriving at the pterygopalatine fossa. Another important structure is the orbital apex with the optic canal, which is crossed by the optic nerve (II) and the superior orbital fissure, which provides a passage for cranial nerves III, IV, VI, and V1 (6).

Clinical Presentation of Patients with SBO

Patients with SBO frequently have nonspecific symptoms such as headache and facial pain, and therefore they exhibit a variety of clinical presentations (7). Most patients start with otitis externa and present with a headache, severe otalgia, facial pain, purulent otorrhea, and, in advanced cases, conductive hearing loss (2,8,9). In other cases, the origin might be a sinus disease, resulting in nasal congestion, rhinorrhea, headache, and fever (2,8).

In our study, cranial nerve palsy was common. In general, patients usually experience lower cranial nerve palsy, because the inflammatory process is near the neural foramina. Because of its proximity to the external auditory canal at the exit of the skull base, one of the nerves that is most frequently affected is cranial nerve VII when the stylomastoid foramen or the mastoid process are involved, and this can cause facial pain and peripheral facial paralysis. This condition can be accompanied by sensorineural hearing loss when cranial nerve VIII is involved. Abducens nerve (VI) palsy can occur if the petrous apex is involved, manifesting as binocular diplopia. If the jugular foramen is affected, palsy can be present in cranial nerves IX, X, and XI and can cause a soft palate mobility disorder, unilateral vocal cord paralysis, and an inability to raise the arm above the horizontal plane, respectively. Similarly, hypoglossal canal involvement causes cranial nerve XII neuropathy, with tongue movement disorders (1,5,7,10).

All but one of our six patients had a history of otitis (three cases of otitis externa and two cases of suppurative otitis media); the other patient had sinusitis. Two patients presented with facial pain, two presented with headaches, and one presented with peripheral facial paralysis (VII nerve palsy). The most affected nerve was cranial nerve VI, in four cases. Other nerves affected were cranial nerves IX and X (Table).

Clinical Information for Six Patients with SBO Studied at the Authors’ Institution

Risk Factors

Patients with SBO typically are elderly and have diabetes or are immunosuppressed. Cerumen from the ears of diabetic patients has a higher pH than that of nondiabetic patients, and it has been posited to provide a more beneficial environment for bacterial overgrowth. Microangiopathic changes in individuals with diabetes also favor the spread of infection and the decrease in antibiotic response (4,7).

Other diseases that alter the vascularization and oxygenation of bone predispose patients to SBO, such as small vessel disease, radiation exposure, malignancy, osteoporosis, osteopetrosis, anemia, malnutrition, and Paget disease of the bone. Other risk factors include cardiovascular disease, renal failure, hepatic failure, obesity, smoking, extended hospital stays, and chronic pulmonary disease (4,7).

In our study, all six patients were men (mean age, 71 years), and three (50%) of them had diabetes. One of the patients had a history of radiation therapy in the cavum secondary to lymphoepithelioma; another had chronic liver disease, aortic valve disease, and hypertension; and one patient was immunosuppressed (Table).

Causes and Routes of Infection

SBO can be classified as otogenic or nonotogenic in origin (8).

Teaching Point SBO frequently has an otogenic origin, typically in patients with diabetes and recurrent otitis externa (1). Other causes of SBO include suppurative otitis media or mastoiditis. In these patients, the infection usually extends inferiorly from the osseous-cartilaginous junction of the external auditory canal, through the vertical fissures of Santorini to the Haversian system of the compact bone of the infratemporal fossa, affecting the lower cranial nerve foramina (Fig 4)
. The facial cranial nerve (VII) is usually the first to be involved at the exit of the stylomastoid foramen (Fig 5). The infection can spread medially to the jugular foramen (with involvement of cranial nerves IX, X, and XI) and the petrous apex (with involvement of cranial nerves V and VI) (Fig 5); anteriorly to the parotid, masticator, or parapharyngeal spaces; posteriorly to the mastoid space (cranial nerve VII involvement); or even intracranially through the petroclival synchondrosis (Fig 4); causing subperiosteal abscesses or epidural or subdural empyemas (4,5,7,9).

Coronal CT image shows the spread of infection (green arrows) in a patient                     with otogenic SBO of the temporal bone. SBO is usually secondary to otitis                     externa. From the external auditory canal, the infection reaches the temporal                     bone through the fissures of Santorini. The infection can spread                     anteroinferiorly to the parotid, masticator, or parapharyngeal spaces, medially                     to the carotid or perivertebral spaces, and even into the spinal canal.                     Intracranial spread can also occur by extension through the petroclival                     synchondrosis.

Figure 4. Coronal CT image shows the spread of infection (green arrows) in a patient with otogenic SBO of the temporal bone. SBO is usually secondary to otitis externa. From the external auditory canal, the infection reaches the temporal bone through the fissures of Santorini. The infection can spread anteroinferiorly to the parotid, masticator, or parapharyngeal spaces, medially to the carotid or perivertebral spaces, and even into the spinal canal. Intracranial spread can also occur by extension through the petroclival synchondrosis.

Axial CT image shows the spread of infection (green arrows) in a patient                     with otogenic SBO in the temporal bone. The infection typically spreads by means                     of vascular and subfascial planes and can reach various skull base foramina. The                     facial nerve (VII) is usually affected when the stylomastoid foramen or mastoid                     process is involved. The infection can spread medially to the jugular foramen,                     with involvement of cranial nerves IX, X, and XI and the jugular vein. The                     carotid canal can also be affected and cause vascular complications. If the                     infection progresses, it can reach the foramen spinosum and foramen                     ovale.

Figure 5. Axial CT image shows the spread of infection (green arrows) in a patient with otogenic SBO in the temporal bone. The infection typically spreads by means of vascular and subfascial planes and can reach various skull base foramina. The facial nerve (VII) is usually affected when the stylomastoid foramen or mastoid process is involved. The infection can spread medially to the jugular foramen, with involvement of cranial nerves IX, X, and XI and the jugular vein. The carotid canal can also be affected and cause vascular complications. If the infection progresses, it can reach the foramen spinosum and foramen ovale.

The nonotogenic origin can be secondary to contiguous spread from another local infection such as a paranasal sinus infection, odontogenic infection, or spontaneous scalp infection. Direct inoculation is another cause of infection and can be iatrogenic (secondary to neurosurgery or cranioplasty, or after mastoidectomy) or posttraumatic (craniofacial injuries, cephalohematoma infection, traumatic scalp hematoma infection, or penetrating craniocerebral injury). Hematogenous dissemination from remote source infections such as those of the lung or spine, peripheral arthritis, and meningitis are other possible but rare routes (11).

Causative Pathogens

An etiologic and microbiologic diagnosis is crucial for the correct treatment, given that the infection can be bacterial or fungal. Several clinical clues can help to differentiate between them before the biopsy results have been obtained. Patients with bacterial SBO are more likely to present with otitis externa, otitis media, or mastoiditis as the focus of infection, developing deafness, otalgia, and purulent ear discharge. In comparison, patients with immunosuppression and chronic sinusitis, sinonasal pain, facial or periorbital swelling, and nasal discharge more frequently have fungal SBO (2,8).

Teaching Point Pseudomonas aeruginosa is the most prevalent bacteria, followed by Staphylococcus aureus. Other bacteria that are seen less frequently include Staphylococcus epidermidis, Salmonella species, Proteus mirabilis, nontuberculous Mycobacterium species, Streptococcus pneumoniae, Treponema pallidum, and Klebsiella species (4,11).

Teaching Point There is general agreement that the most frequently seen fungus is Aspergillus species, although it depends on the study.
Other fungal causes are Candida species, Cryptococcus neoformans, Blastomyces species, Mucor species, and Rhizopus species (11).

In our study, the most frequently encountered pathogen was also P aeruginosa in three patients, two of whom had coinfection with another pathogen (patient 3 with S aureus, and patient 4 with Candida parapsilosis). One patient presented with Candida albicans, while another presented with Streptococcus species. The pathogen for patient 5 was not determined (Table).

Imaging Findings

The imaging techniques used to diagnose SBO are nonenhanced and contrast-enhanced CT, enhanced MRI, and nuclear imaging. We describe the imaging findings of the six patients who received a diagnosis of SBO in our hospital between 2015 and 2020 (Figs 614).

Patient 1, a 57-year-old man with lymphoepithelial carcinoma of the                     nasopharynx who was treated with chemotherapy and radiation therapy in 2005. In                     2011, the patient experienced chronic rhinosinusitis and underwent                     contrast-enhanced CT, which showed sphenoid body erosion secondary to the                     previous treatment. (a) Sagittal nonenhanced CT image acquired in 2015 shows                     that the sphenoid erosion had grown (double-headed arrow) since the 2011 imaging                     study (not shown). (b) Sagittal contrast-enhanced T1-weighted MR image acquired                     in 2017 shows sphenoid erosion (blue double-headed arrow), with thickening and                     an area of contrast material enhancement (purple arrows). A differential                     diagnosis of tumor relapse versus an inflammatory process was proposed. (c)                     Technetium 99m (99mTc)–exametazime–labeled leukocyte scintigram                     shows sphenoid and right maxillary sinus osteomyelitis. (d) Three-dimensional                     arteriogram acquired in 2018 after the patient expressed concern about recurrent                     epistaxis shows a pseudoaneurysm (oval) of the right cavernous internal carotid                     artery, which was embolized.

Figure 6a. Patient 1, a 57-year-old man with lymphoepithelial carcinoma of the nasopharynx who was treated with chemotherapy and radiation therapy in 2005. In 2011, the patient experienced chronic rhinosinusitis and underwent contrast-enhanced CT, which showed sphenoid body erosion secondary to the previous treatment. (a) Sagittal nonenhanced CT image acquired in 2015 shows that the sphenoid erosion had grown (double-headed arrow) since the 2011 imaging study (not shown). (b) Sagittal contrast-enhanced T1-weighted MR image acquired in 2017 shows sphenoid erosion (blue double-headed arrow), with thickening and an area of contrast material enhancement (purple arrows). A differential diagnosis of tumor relapse versus an inflammatory process was proposed. (c) Technetium 99m (99mTc)–exametazime–labeled leukocyte scintigram shows sphenoid and right maxillary sinus osteomyelitis. (d) Three-dimensional arteriogram acquired in 2018 after the patient expressed concern about recurrent epistaxis shows a pseudoaneurysm (oval) of the right cavernous internal carotid artery, which was embolized.

Patient 1, a 57-year-old man with lymphoepithelial carcinoma of the                     nasopharynx who was treated with chemotherapy and radiation therapy in 2005. In                     2011, the patient experienced chronic rhinosinusitis and underwent                     contrast-enhanced CT, which showed sphenoid body erosion secondary to the                     previous treatment. (a) Sagittal nonenhanced CT image acquired in 2015 shows                     that the sphenoid erosion had grown (double-headed arrow) since the 2011 imaging                     study (not shown). (b) Sagittal contrast-enhanced T1-weighted MR image acquired                     in 2017 shows sphenoid erosion (blue double-headed arrow), with thickening and                     an area of contrast material enhancement (purple arrows). A differential                     diagnosis of tumor relapse versus an inflammatory process was proposed. (c)                     Technetium 99m (99mTc)–exametazime–labeled leukocyte scintigram                     shows sphenoid and right maxillary sinus osteomyelitis. (d) Three-dimensional                     arteriogram acquired in 2018 after the patient expressed concern about recurrent                     epistaxis shows a pseudoaneurysm (oval) of the right cavernous internal carotid                     artery, which was embolized.

Figure 6b. Patient 1, a 57-year-old man with lymphoepithelial carcinoma of the nasopharynx who was treated with chemotherapy and radiation therapy in 2005. In 2011, the patient experienced chronic rhinosinusitis and underwent contrast-enhanced CT, which showed sphenoid body erosion secondary to the previous treatment. (a) Sagittal nonenhanced CT image acquired in 2015 shows that the sphenoid erosion had grown (double-headed arrow) since the 2011 imaging study (not shown). (b) Sagittal contrast-enhanced T1-weighted MR image acquired in 2017 shows sphenoid erosion (blue double-headed arrow), with thickening and an area of contrast material enhancement (purple arrows). A differential diagnosis of tumor relapse versus an inflammatory process was proposed. (c) Technetium 99m (99mTc)–exametazime–labeled leukocyte scintigram shows sphenoid and right maxillary sinus osteomyelitis. (d) Three-dimensional arteriogram acquired in 2018 after the patient expressed concern about recurrent epistaxis shows a pseudoaneurysm (oval) of the right cavernous internal carotid artery, which was embolized.

Patient 1, a 57-year-old man with lymphoepithelial carcinoma of the                     nasopharynx who was treated with chemotherapy and radiation therapy in 2005. In                     2011, the patient experienced chronic rhinosinusitis and underwent                     contrast-enhanced CT, which showed sphenoid body erosion secondary to the                     previous treatment. (a) Sagittal nonenhanced CT image acquired in 2015 shows                     that the sphenoid erosion had grown (double-headed arrow) since the 2011 imaging                     study (not shown). (b) Sagittal contrast-enhanced T1-weighted MR image acquired                     in 2017 shows sphenoid erosion (blue double-headed arrow), with thickening and                     an area of contrast material enhancement (purple arrows). A differential                     diagnosis of tumor relapse versus an inflammatory process was proposed. (c)                     Technetium 99m (99mTc)–exametazime–labeled leukocyte scintigram                     shows sphenoid and right maxillary sinus osteomyelitis. (d) Three-dimensional                     arteriogram acquired in 2018 after the patient expressed concern about recurrent                     epistaxis shows a pseudoaneurysm (oval) of the right cavernous internal carotid                     artery, which was embolized.

Figure 6c. Patient 1, a 57-year-old man with lymphoepithelial carcinoma of the nasopharynx who was treated with chemotherapy and radiation therapy in 2005. In 2011, the patient experienced chronic rhinosinusitis and underwent contrast-enhanced CT, which showed sphenoid body erosion secondary to the previous treatment. (a) Sagittal nonenhanced CT image acquired in 2015 shows that the sphenoid erosion had grown (double-headed arrow) since the 2011 imaging study (not shown). (b) Sagittal contrast-enhanced T1-weighted MR image acquired in 2017 shows sphenoid erosion (blue double-headed arrow), with thickening and an area of contrast material enhancement (purple arrows). A differential diagnosis of tumor relapse versus an inflammatory process was proposed. (c) Technetium 99m (99mTc)–exametazime–labeled leukocyte scintigram shows sphenoid and right maxillary sinus osteomyelitis. (d) Three-dimensional arteriogram acquired in 2018 after the patient expressed concern about recurrent epistaxis shows a pseudoaneurysm (oval) of the right cavernous internal carotid artery, which was embolized.

Patient 1, a 57-year-old man with lymphoepithelial carcinoma of the                     nasopharynx who was treated with chemotherapy and radiation therapy in 2005. In                     2011, the patient experienced chronic rhinosinusitis and underwent                     contrast-enhanced CT, which showed sphenoid body erosion secondary to the                     previous treatment. (a) Sagittal nonenhanced CT image acquired in 2015 shows                     that the sphenoid erosion had grown (double-headed arrow) since the 2011 imaging                     study (not shown). (b) Sagittal contrast-enhanced T1-weighted MR image acquired                     in 2017 shows sphenoid erosion (blue double-headed arrow), with thickening and                     an area of contrast material enhancement (purple arrows). A differential                     diagnosis of tumor relapse versus an inflammatory process was proposed. (c)                     Technetium 99m (99mTc)–exametazime–labeled leukocyte scintigram                     shows sphenoid and right maxillary sinus osteomyelitis. (d) Three-dimensional                     arteriogram acquired in 2018 after the patient expressed concern about recurrent                     epistaxis shows a pseudoaneurysm (oval) of the right cavernous internal carotid                     artery, which was embolized.

Figure 6d. Patient 1, a 57-year-old man with lymphoepithelial carcinoma of the nasopharynx who was treated with chemotherapy and radiation therapy in 2005. In 2011, the patient experienced chronic rhinosinusitis and underwent contrast-enhanced CT, which showed sphenoid body erosion secondary to the previous treatment. (a) Sagittal nonenhanced CT image acquired in 2015 shows that the sphenoid erosion had grown (double-headed arrow) since the 2011 imaging study (not shown). (b) Sagittal contrast-enhanced T1-weighted MR image acquired in 2017 shows sphenoid erosion (blue double-headed arrow), with thickening and an area of contrast material enhancement (purple arrows). A differential diagnosis of tumor relapse versus an inflammatory process was proposed. (c) Technetium 99m (99mTc)–exametazime–labeled leukocyte scintigram shows sphenoid and right maxillary sinus osteomyelitis. (d) Three-dimensional arteriogram acquired in 2018 after the patient expressed concern about recurrent epistaxis shows a pseudoaneurysm (oval) of the right cavernous internal carotid artery, which was embolized.

Patient 2, a 77-year-old man with right facial pain that started 3 months                     earlier. (a) Axial contrast-enhanced CT image shows an ill-defined poorly                     enhancing mass (circle) in the right posterolateral wall of the nasopharynx. (b)                     Axial contrast-enhanced CT image shows that the mass is included in the right                     internal carotid artery (red dot) and internal jugular vein (blue dot), which                     was compressed. (c) Axial contrast-enhanced CT image shows erosion of the bone                     margins (arrows) adjacent to the mass, with the right facial nerve canal (oval)                     affected. (d) Axial contrast-enhanced CT image shows middle ear and mastoid                     process changes secondary to chronic otomastoiditis (arrows). These findings                     were interpreted as an aggressive nasopharyngeal neoplasia.

Figure 7a. Patient 2, a 77-year-old man with right facial pain that started 3 months earlier. (a) Axial contrast-enhanced CT image shows an ill-defined poorly enhancing mass (circle) in the right posterolateral wall of the nasopharynx. (b) Axial contrast-enhanced CT image shows that the mass is included in the right internal carotid artery (red dot) and internal jugular vein (blue dot), which was compressed. (c) Axial contrast-enhanced CT image shows erosion of the bone margins (arrows) adjacent to the mass, with the right facial nerve canal (oval) affected. (d) Axial contrast-enhanced CT image shows middle ear and mastoid process changes secondary to chronic otomastoiditis (arrows). These findings were interpreted as an aggressive nasopharyngeal neoplasia.

Patient 2, a 77-year-old man with right facial pain that started 3 months                     earlier. (a) Axial contrast-enhanced CT image shows an ill-defined poorly                     enhancing mass (circle) in the right posterolateral wall of the nasopharynx. (b)                     Axial contrast-enhanced CT image shows that the mass is included in the right                     internal carotid artery (red dot) and internal jugular vein (blue dot), which                     was compressed. (c) Axial contrast-enhanced CT image shows erosion of the bone                     margins (arrows) adjacent to the mass, with the right facial nerve canal (oval)                     affected. (d) Axial contrast-enhanced CT image shows middle ear and mastoid                     process changes secondary to chronic otomastoiditis (arrows). These findings                     were interpreted as an aggressive nasopharyngeal neoplasia.

Figure 7b. Patient 2, a 77-year-old man with right facial pain that started 3 months earlier. (a) Axial contrast-enhanced CT image shows an ill-defined poorly enhancing mass (circle) in the right posterolateral wall of the nasopharynx. (b) Axial contrast-enhanced CT image shows that the mass is included in the right internal carotid artery (red dot) and internal jugular vein (blue dot), which was compressed. (c) Axial contrast-enhanced CT image shows erosion of the bone margins (arrows) adjacent to the mass, with the right facial nerve canal (oval) affected. (d) Axial contrast-enhanced CT image shows middle ear and mastoid process changes secondary to chronic otomastoiditis (arrows). These findings were interpreted as an aggressive nasopharyngeal neoplasia.

Patient 2, a 77-year-old man with right facial pain that started 3 months                     earlier. (a) Axial contrast-enhanced CT image shows an ill-defined poorly                     enhancing mass (circle) in the right posterolateral wall of the nasopharynx. (b)                     Axial contrast-enhanced CT image shows that the mass is included in the right                     internal carotid artery (red dot) and internal jugular vein (blue dot), which                     was compressed. (c) Axial contrast-enhanced CT image shows erosion of the bone                     margins (arrows) adjacent to the mass, with the right facial nerve canal (oval)                     affected. (d) Axial contrast-enhanced CT image shows middle ear and mastoid                     process changes secondary to chronic otomastoiditis (arrows). These findings                     were interpreted as an aggressive nasopharyngeal neoplasia.

Figure 7c. Patient 2, a 77-year-old man with right facial pain that started 3 months earlier. (a) Axial contrast-enhanced CT image shows an ill-defined poorly enhancing mass (circle) in the right posterolateral wall of the nasopharynx. (b) Axial contrast-enhanced CT image shows that the mass is included in the right internal carotid artery (red dot) and internal jugular vein (blue dot), which was compressed. (c) Axial contrast-enhanced CT image shows erosion of the bone margins (arrows) adjacent to the mass, with the right facial nerve canal (oval) affected. (d) Axial contrast-enhanced CT image shows middle ear and mastoid process changes secondary to chronic otomastoiditis (arrows). These findings were interpreted as an aggressive nasopharyngeal neoplasia.

Patient 2, a 77-year-old man with right facial pain that started 3 months                     earlier. (a) Axial contrast-enhanced CT image shows an ill-defined poorly                     enhancing mass (circle) in the right posterolateral wall of the nasopharynx. (b)                     Axial contrast-enhanced CT image shows that the mass is included in the right                     internal carotid artery (red dot) and internal jugular vein (blue dot), which                     was compressed. (c) Axial contrast-enhanced CT image shows erosion of the bone                     margins (arrows) adjacent to the mass, with the right facial nerve canal (oval)                     affected. (d) Axial contrast-enhanced CT image shows middle ear and mastoid                     process changes secondary to chronic otomastoiditis (arrows). These findings                     were interpreted as an aggressive nasopharyngeal neoplasia.

Figure 7d. Patient 2, a 77-year-old man with right facial pain that started 3 months earlier. (a) Axial contrast-enhanced CT image shows an ill-defined poorly enhancing mass (circle) in the right posterolateral wall of the nasopharynx. (b) Axial contrast-enhanced CT image shows that the mass is included in the right internal carotid artery (red dot) and internal jugular vein (blue dot), which was compressed. (c) Axial contrast-enhanced CT image shows erosion of the bone margins (arrows) adjacent to the mass, with the right facial nerve canal (oval) affected. (d) Axial contrast-enhanced CT image shows middle ear and mastoid process changes secondary to chronic otomastoiditis (arrows). These findings were interpreted as an aggressive nasopharyngeal neoplasia.

Patient 2, a 77-year-old man with right facial pain (see also Fig 7), 6                     months after the onset of symptoms. Repeated biopsies were performed, with                     results that were negative for malignancy. (a, b) Axial (a) and sagittal (b)                     contrast-enhanced T1-weighted MR images show an inflammatory area extending                     along the parapharyngeal (light green arrows in a), retropharyngeal (dark green                     arrows in a and b), perivertebral (brown arrows in b), and epidural (purple                     arrows in b) spaces. (c, d) Axial contrast-enhanced T1-weighted (c) and                     diffusion-weighted (d) MR images show abscess formation (blue oval) in the                     retropharyngeal and perivertebral spaces. The left internal carotid artery (red                     dot in c) was enlarged, and CT angiography was requested. The imaging findings,                     negative biopsies, and clinical progression suggested the diagnosis of SBO                     complicated by an abscess.

Figure 8a. Patient 2, a 77-year-old man with right facial pain (see also Fig 7), 6 months after the onset of symptoms. Repeated biopsies were performed, with results that were negative for malignancy. (a, b) Axial (a) and sagittal (b) contrast-enhanced T1-weighted MR images show an inflammatory area extending along the parapharyngeal (light green arrows in a), retropharyngeal (dark green arrows in a and b), perivertebral (brown arrows in b), and epidural (purple arrows in b) spaces. (c, d) Axial contrast-enhanced T1-weighted (c) and diffusion-weighted (d) MR images show abscess formation (blue oval) in the retropharyngeal and perivertebral spaces. The left internal carotid artery (red dot in c) was enlarged, and CT angiography was requested. The imaging findings, negative biopsies, and clinical progression suggested the diagnosis of SBO complicated by an abscess.

Patient 2, a 77-year-old man with right facial pain (see also Fig 7), 6                     months after the onset of symptoms. Repeated biopsies were performed, with                     results that were negative for malignancy. (a, b) Axial (a) and sagittal (b)                     contrast-enhanced T1-weighted MR images show an inflammatory area extending                     along the parapharyngeal (light green arrows in a), retropharyngeal (dark green                     arrows in a and b), perivertebral (brown arrows in b), and epidural (purple                     arrows in b) spaces. (c, d) Axial contrast-enhanced T1-weighted (c) and                     diffusion-weighted (d) MR images show abscess formation (blue oval) in the                     retropharyngeal and perivertebral spaces. The left internal carotid artery (red                     dot in c) was enlarged, and CT angiography was requested. The imaging findings,                     negative biopsies, and clinical progression suggested the diagnosis of SBO                     complicated by an abscess.

Figure 8b. Patient 2, a 77-year-old man with right facial pain (see also Fig 7), 6 months after the onset of symptoms. Repeated biopsies were performed, with results that were negative for malignancy. (a, b) Axial (a) and sagittal (b) contrast-enhanced T1-weighted MR images show an inflammatory area extending along the parapharyngeal (light green arrows in a), retropharyngeal (dark green arrows in a and b), perivertebral (brown arrows in b), and epidural (purple arrows in b) spaces. (c, d) Axial contrast-enhanced T1-weighted (c) and diffusion-weighted (d) MR images show abscess formation (blue oval) in the retropharyngeal and perivertebral spaces. The left internal carotid artery (red dot in c) was enlarged, and CT angiography was requested. The imaging findings, negative biopsies, and clinical progression suggested the diagnosis of SBO complicated by an abscess.

Patient 2, a 77-year-old man with right facial pain (see also Fig 7), 6                     months after the onset of symptoms. Repeated biopsies were performed, with                     results that were negative for malignancy. (a, b) Axial (a) and sagittal (b)                     contrast-enhanced T1-weighted MR images show an inflammatory area extending                     along the parapharyngeal (light green arrows in a), retropharyngeal (dark green                     arrows in a and b), perivertebral (brown arrows in b), and epidural (purple                     arrows in b) spaces. (c, d) Axial contrast-enhanced T1-weighted (c) and                     diffusion-weighted (d) MR images show abscess formation (blue oval) in the                     retropharyngeal and perivertebral spaces. The left internal carotid artery (red                     dot in c) was enlarged, and CT angiography was requested. The imaging findings,                     negative biopsies, and clinical progression suggested the diagnosis of SBO                     complicated by an abscess.

Figure 8c. Patient 2, a 77-year-old man with right facial pain (see also Fig 7), 6 months after the onset of symptoms. Repeated biopsies were performed, with results that were negative for malignancy. (a, b) Axial (a) and sagittal (b) contrast-enhanced T1-weighted MR images show an inflammatory area extending along the parapharyngeal (light green arrows in a), retropharyngeal (dark green arrows in a and b), perivertebral (brown arrows in b), and epidural (purple arrows in b) spaces. (c, d) Axial contrast-enhanced T1-weighted (c) and diffusion-weighted (d) MR images show abscess formation (blue oval) in the retropharyngeal and perivertebral spaces. The left internal carotid artery (red dot in c) was enlarged, and CT angiography was requested. The imaging findings, negative biopsies, and clinical progression suggested the diagnosis of SBO complicated by an abscess.

Patient 2, a 77-year-old man with right facial pain (see also Fig 7), 6                     months after the onset of symptoms. Repeated biopsies were performed, with                     results that were negative for malignancy. (a, b) Axial (a) and sagittal (b)                     contrast-enhanced T1-weighted MR images show an inflammatory area extending                     along the parapharyngeal (light green arrows in a), retropharyngeal (dark green                     arrows in a and b), perivertebral (brown arrows in b), and epidural (purple                     arrows in b) spaces. (c, d) Axial contrast-enhanced T1-weighted (c) and                     diffusion-weighted (d) MR images show abscess formation (blue oval) in the                     retropharyngeal and perivertebral spaces. The left internal carotid artery (red                     dot in c) was enlarged, and CT angiography was requested. The imaging findings,                     negative biopsies, and clinical progression suggested the diagnosis of SBO                     complicated by an abscess.

Figure 8d. Patient 2, a 77-year-old man with right facial pain (see also Fig 7), 6 months after the onset of symptoms. Repeated biopsies were performed, with results that were negative for malignancy. (a, b) Axial (a) and sagittal (b) contrast-enhanced T1-weighted MR images show an inflammatory area extending along the parapharyngeal (light green arrows in a), retropharyngeal (dark green arrows in a and b), perivertebral (brown arrows in b), and epidural (purple arrows in b) spaces. (c, d) Axial contrast-enhanced T1-weighted (c) and diffusion-weighted (d) MR images show abscess formation (blue oval) in the retropharyngeal and perivertebral spaces. The left internal carotid artery (red dot in c) was enlarged, and CT angiography was requested. The imaging findings, negative biopsies, and clinical progression suggested the diagnosis of SBO complicated by an abscess.

Patient 2 (same patient as in Figs 7 and 8). Coronal contrast-enhanced CT                     angiogram (a), three-dimensional reconstruction (b), and arteriogram (c) show a                     pseudoaneurysm (arrows) of the left internal carotid artery from its distal                     cervical segment to the carotid canal. The findings were determined to be SBO                     complicated by a mycotic pseudoaneurysm.

Figure 9a. Patient 2 (same patient as in Figs 7 and 8). Coronal contrast-enhanced CT angiogram (a), three-dimensional reconstruction (b), and arteriogram (c) show a pseudoaneurysm (arrows) of the left internal carotid artery from its distal cervical segment to the carotid canal. The findings were determined to be SBO complicated by a mycotic pseudoaneurysm.

Patient 2 (same patient as in Figs 7 and 8). Coronal contrast-enhanced CT                     angiogram (a), three-dimensional reconstruction (b), and arteriogram (c) show a                     pseudoaneurysm (arrows) of the left internal carotid artery from its distal                     cervical segment to the carotid canal. The findings were determined to be SBO                     complicated by a mycotic pseudoaneurysm.

Figure 9b. Patient 2 (same patient as in Figs 7 and 8). Coronal contrast-enhanced CT angiogram (a), three-dimensional reconstruction (b), and arteriogram (c) show a pseudoaneurysm (arrows) of the left internal carotid artery from its distal cervical segment to the carotid canal. The findings were determined to be SBO complicated by a mycotic pseudoaneurysm.

Patient 2 (same patient as in Figs 7 and 8). Coronal contrast-enhanced CT                     angiogram (a), three-dimensional reconstruction (b), and arteriogram (c) show a                     pseudoaneurysm (arrows) of the left internal carotid artery from its distal                     cervical segment to the carotid canal. The findings were determined to be SBO                     complicated by a mycotic pseudoaneurysm.

Figure 9c. Patient 2 (same patient as in Figs 7 and 8). Coronal contrast-enhanced CT angiogram (a), three-dimensional reconstruction (b), and arteriogram (c) show a pseudoaneurysm (arrows) of the left internal carotid artery from its distal cervical segment to the carotid canal. The findings were determined to be SBO complicated by a mycotic pseudoaneurysm.

Patient 3, a 71-year-old man with right otitis externa, facial pain, and                     peripheral facial paralysis. (a) Axial contrast-enhanced CT image shows                     opacification of the right middle ear (orange arrows) and mastoid cells (purple                     arrows) and bone erosion (green arrow) of the anterior margin of the                     epitympanum. (b) Axial contrast-enhanced CT image shows a poorly enhancing mass                     (circle) in the right posterolateral wall of the nasopharynx. (c, d) Axial                     contrast-enhanced T1-weighted MR images show extension to the right                     pterygopalatine fossa (pink arrow in c), trigeminal cavity (green arrow in c),                     carotid space (red arrows in c), masticator space (yellow arrows in d), and                     parapharyngeal and mucosal pharyngeal spaces (light blue arrows in d). The                     findings were interpreted as a nasopharyngeal carcinoma.

Figure 10a. Patient 3, a 71-year-old man with right otitis externa, facial pain, and peripheral facial paralysis. (a) Axial contrast-enhanced CT image shows opacification of the right middle ear (orange arrows) and mastoid cells (purple arrows) and bone erosion (green arrow) of the anterior margin of the epitympanum. (b) Axial contrast-enhanced CT image shows a poorly enhancing mass (circle) in the right posterolateral wall of the nasopharynx. (c, d) Axial contrast-enhanced T1-weighted MR images show extension to the right pterygopalatine fossa (pink arrow in c), trigeminal cavity (green arrow in c), carotid space (red arrows in c), masticator space (yellow arrows in d), and parapharyngeal and mucosal pharyngeal spaces (light blue arrows in d). The findings were interpreted as a nasopharyngeal carcinoma.

Patient 3, a 71-year-old man with right otitis externa, facial pain, and                     peripheral facial paralysis. (a) Axial contrast-enhanced CT image shows                     opacification of the right middle ear (orange arrows) and mastoid cells (purple                     arrows) and bone erosion (green arrow) of the anterior margin of the                     epitympanum. (b) Axial contrast-enhanced CT image shows a poorly enhancing mass                     (circle) in the right posterolateral wall of the nasopharynx. (c, d) Axial                     contrast-enhanced T1-weighted MR images show extension to the right                     pterygopalatine fossa (pink arrow in c), trigeminal cavity (green arrow in c),                     carotid space (red arrows in c), masticator space (yellow arrows in d), and                     parapharyngeal and mucosal pharyngeal spaces (light blue arrows in d). The                     findings were interpreted as a nasopharyngeal carcinoma.

Figure 10b. Patient 3, a 71-year-old man with right otitis externa, facial pain, and peripheral facial paralysis. (a) Axial contrast-enhanced CT image shows opacification of the right middle ear (orange arrows) and mastoid cells (purple arrows) and bone erosion (green arrow) of the anterior margin of the epitympanum. (b) Axial contrast-enhanced CT image shows a poorly enhancing mass (circle) in the right posterolateral wall of the nasopharynx. (c, d) Axial contrast-enhanced T1-weighted MR images show extension to the right pterygopalatine fossa (pink arrow in c), trigeminal cavity (green arrow in c), carotid space (red arrows in c), masticator space (yellow arrows in d), and parapharyngeal and mucosal pharyngeal spaces (light blue arrows in d). The findings were interpreted as a nasopharyngeal carcinoma.

Patient 3, a 71-year-old man with right otitis externa, facial pain, and                     peripheral facial paralysis. (a) Axial contrast-enhanced CT image shows                     opacification of the right middle ear (orange arrows) and mastoid cells (purple                     arrows) and bone erosion (green arrow) of the anterior margin of the                     epitympanum. (b) Axial contrast-enhanced CT image shows a poorly enhancing mass                     (circle) in the right posterolateral wall of the nasopharynx. (c, d) Axial                     contrast-enhanced T1-weighted MR images show extension to the right                     pterygopalatine fossa (pink arrow in c), trigeminal cavity (green arrow in c),                     carotid space (red arrows in c), masticator space (yellow arrows in d), and                     parapharyngeal and mucosal pharyngeal spaces (light blue arrows in d). The                     findings were interpreted as a nasopharyngeal carcinoma.

Figure 10c. Patient 3, a 71-year-old man with right otitis externa, facial pain, and peripheral facial paralysis. (a) Axial contrast-enhanced CT image shows opacification of the right middle ear (orange arrows) and mastoid cells (purple arrows) and bone erosion (green arrow) of the anterior margin of the epitympanum. (b) Axial contrast-enhanced CT image shows a poorly enhancing mass (circle) in the right posterolateral wall of the nasopharynx. (c, d) Axial contrast-enhanced T1-weighted MR images show extension to the right pterygopalatine fossa (pink arrow in c), trigeminal cavity (green arrow in c), carotid space (red arrows in c), masticator space (yellow arrows in d), and parapharyngeal and mucosal pharyngeal spaces (light blue arrows in d). The findings were interpreted as a nasopharyngeal carcinoma.

Patient 3, a 71-year-old man with right otitis externa, facial pain, and                     peripheral facial paralysis. (a) Axial contrast-enhanced CT image shows                     opacification of the right middle ear (orange arrows) and mastoid cells (purple                     arrows) and bone erosion (green arrow) of the anterior margin of the                     epitympanum. (b) Axial contrast-enhanced CT image shows a poorly enhancing mass                     (circle) in the right posterolateral wall of the nasopharynx. (c, d) Axial                     contrast-enhanced T1-weighted MR images show extension to the right                     pterygopalatine fossa (pink arrow in c), trigeminal cavity (green arrow in c),                     carotid space (red arrows in c), masticator space (yellow arrows in d), and                     parapharyngeal and mucosal pharyngeal spaces (light blue arrows in d). The                     findings were interpreted as a nasopharyngeal carcinoma.

Figure 10d. Patient 3, a 71-year-old man with right otitis externa, facial pain, and peripheral facial paralysis. (a) Axial contrast-enhanced CT image shows opacification of the right middle ear (orange arrows) and mastoid cells (purple arrows) and bone erosion (green arrow) of the anterior margin of the epitympanum. (b) Axial contrast-enhanced CT image shows a poorly enhancing mass (circle) in the right posterolateral wall of the nasopharynx. (c, d) Axial contrast-enhanced T1-weighted MR images show extension to the right pterygopalatine fossa (pink arrow in c), trigeminal cavity (green arrow in c), carotid space (red arrows in c), masticator space (yellow arrows in d), and parapharyngeal and mucosal pharyngeal spaces (light blue arrows in d). The findings were interpreted as a nasopharyngeal carcinoma.

Patient 3, a 71-year-old man (see also Fig 10), who underwent endoscopic                     transnasal surgery after which the pathologic report showed no signs of                     malignancy. Three months after surgery, the facial pain persisted and the                     patient had associated weight loss, loss of vision in the left eye, severe                     bilateral hearing loss, dysphagia to solids, and dysphonia. (a, b) Sagittal (a)                     and axial (b) contrast-enhanced T1-weighted MR images show an inflammation                     around the clivus (blue-green arrows), the petrous part of the temporal bones                     (olive green arrows in b), and the occipital condyles (orange arrows in b) and                     thrombosis of the left internal jugular vein (light blue arrow in b), sigmoid                     sinus (dark purple arrows in b), and transverse sinus (purple arrows in b). The                     findings suggest the diagnosis of complicated SBO. (c) 99mTc SPECT/CT images                     show findings that are in agreement with the diagnosis of sphenoid and occipital                     osteomyelitis.

Figure 11a. Patient 3, a 71-year-old man (see also Fig 10), who underwent endoscopic transnasal surgery after which the pathologic report showed no signs of malignancy. Three months after surgery, the facial pain persisted and the patient had associated weight loss, loss of vision in the left eye, severe bilateral hearing loss, dysphagia to solids, and dysphonia. (a, b) Sagittal (a) and axial (b) contrast-enhanced T1-weighted MR images show an inflammation around the clivus (blue-green arrows), the petrous part of the temporal bones (olive green arrows in b), and the occipital condyles (orange arrows in b) and thrombosis of the left internal jugular vein (light blue arrow in b), sigmoid sinus (dark purple arrows in b), and transverse sinus (purple arrows in b). The findings suggest the diagnosis of complicated SBO. (c) 99mTc SPECT/CT images show findings that are in agreement with the diagnosis of sphenoid and occipital osteomyelitis.

Patient 3, a 71-year-old man (see also Fig 10), who underwent endoscopic                     transnasal surgery after which the pathologic report showed no signs of                     malignancy. Three months after surgery, the facial pain persisted and the                     patient had associated weight loss, loss of vision in the left eye, severe                     bilateral hearing loss, dysphagia to solids, and dysphonia. (a, b) Sagittal (a)                     and axial (b) contrast-enhanced T1-weighted MR images show an inflammation                     around the clivus (blue-green arrows), the petrous part of the temporal bones                     (olive green arrows in b), and the occipital condyles (orange arrows in b) and                     thrombosis of the left internal jugular vein (light blue arrow in b), sigmoid                     sinus (dark purple arrows in b), and transverse sinus (purple arrows in b). The                     findings suggest the diagnosis of complicated SBO. (c) 99mTc SPECT/CT images                     show findings that are in agreement with the diagnosis of sphenoid and occipital                     osteomyelitis.

Figure 11b. Patient 3, a 71-year-old man (see also Fig 10), who underwent endoscopic transnasal surgery after which the pathologic report showed no signs of malignancy. Three months after surgery, the facial pain persisted and the patient had associated weight loss, loss of vision in the left eye, severe bilateral hearing loss, dysphagia to solids, and dysphonia. (a, b) Sagittal (a) and axial (b) contrast-enhanced T1-weighted MR images show an inflammation around the clivus (blue-green arrows), the petrous part of the temporal bones (olive green arrows in b), and the occipital condyles (orange arrows in b) and thrombosis of the left internal jugular vein (light blue arrow in b), sigmoid sinus (dark purple arrows in b), and transverse sinus (purple arrows in b). The findings suggest the diagnosis of complicated SBO. (c) 99mTc SPECT/CT images show findings that are in agreement with the diagnosis of sphenoid and occipital osteomyelitis.

Patient 3, a 71-year-old man (see also Fig 10), who underwent endoscopic                     transnasal surgery after which the pathologic report showed no signs of                     malignancy. Three months after surgery, the facial pain persisted and the                     patient had associated weight loss, loss of vision in the left eye, severe                     bilateral hearing loss, dysphagia to solids, and dysphonia. (a, b) Sagittal (a)                     and axial (b) contrast-enhanced T1-weighted MR images show an inflammation                     around the clivus (blue-green arrows), the petrous part of the temporal bones                     (olive green arrows in b), and the occipital condyles (orange arrows in b) and                     thrombosis of the left internal jugular vein (light blue arrow in b), sigmoid                     sinus (dark purple arrows in b), and transverse sinus (purple arrows in b). The                     findings suggest the diagnosis of complicated SBO. (c) 99mTc SPECT/CT images                     show findings that are in agreement with the diagnosis of sphenoid and occipital                     osteomyelitis.

Figure 11c. Patient 3, a 71-year-old man (see also Fig 10), who underwent endoscopic transnasal surgery after which the pathologic report showed no signs of malignancy. Three months after surgery, the facial pain persisted and the patient had associated weight loss, loss of vision in the left eye, severe bilateral hearing loss, dysphagia to solids, and dysphonia. (a, b) Sagittal (a) and axial (b) contrast-enhanced T1-weighted MR images show an inflammation around the clivus (blue-green arrows), the petrous part of the temporal bones (olive green arrows in b), and the occipital condyles (orange arrows in b) and thrombosis of the left internal jugular vein (light blue arrow in b), sigmoid sinus (dark purple arrows in b), and transverse sinus (purple arrows in b). The findings suggest the diagnosis of complicated SBO. (c) 99mTc SPECT/CT images show findings that are in agreement with the diagnosis of sphenoid and occipital osteomyelitis.

Patient 4, a 74-year-old man with chronic suppurative otitis media who                     underwent right myringotomy, but the symptoms and headache persisted. (a)                     Coronal contrast-enhanced CT image shows opacification of the right middle ear                     and mastoid cells (orange arrows) and bone erosion of the right mastoid process                     (lavender arrow). The right stylomastoid foramen was expanded (green arrow). (b)                     Axial contrast-enhanced CT image shows an inflammatory area around the right                     mastoid process, with fat stranding (blue circle). There is sclerosis of the                     right maxillary sinus (green arrows). All of these findings were secondary to                     acute otomastoiditis. At 2 months after the myringotomy, right cortical                     mastoidectomy was performed. (c) Axial nonenhanced CT image shows the right                     cortical mastoidectomy (light brown arrows) and occupation of the remaining                     mastoid cells. Two months after the mastoidectomy, the ear secretion continued.                     (d, e) Axial contrast-enhanced CT image (d) and axial contrast-enhanced                     T1-weighted MR image (e) show an inflammatory process in the right                     posterolateral wall of the nasopharynx (pink arrows) with partial thrombosis of                     the right internal jugular vein (blue arrow in e) and clivus erosion (green                     arrows in d). The findings suggested SBO.

Figure 12a. Patient 4, a 74-year-old man with chronic suppurative otitis media who underwent right myringotomy, but the symptoms and headache persisted. (a) Coronal contrast-enhanced CT image shows opacification of the right middle ear and mastoid cells (orange arrows) and bone erosion of the right mastoid process (lavender arrow). The right stylomastoid foramen was expanded (green arrow). (b) Axial contrast-enhanced CT image shows an inflammatory area around the right mastoid process, with fat stranding (blue circle). There is sclerosis of the right maxillary sinus (green arrows). All of these findings were secondary to acute otomastoiditis. At 2 months after the myringotomy, right cortical mastoidectomy was performed. (c) Axial nonenhanced CT image shows the right cortical mastoidectomy (light brown arrows) and occupation of the remaining mastoid cells. Two months after the mastoidectomy, the ear secretion continued. (d, e) Axial contrast-enhanced CT image (d) and axial contrast-enhanced T1-weighted MR image (e) show an inflammatory process in the right posterolateral wall of the nasopharynx (pink arrows) with partial thrombosis of the right internal jugular vein (blue arrow in e) and clivus erosion (green arrows in d). The findings suggested SBO.

Patient 4, a 74-year-old man with chronic suppurative otitis media who                     underwent right myringotomy, but the symptoms and headache persisted. (a)                     Coronal contrast-enhanced CT image shows opacification of the right middle ear                     and mastoid cells (orange arrows) and bone erosion of the right mastoid process                     (lavender arrow). The right stylomastoid foramen was expanded (green arrow). (b)                     Axial contrast-enhanced CT image shows an inflammatory area around the right                     mastoid process, with fat stranding (blue circle). There is sclerosis of the                     right maxillary sinus (green arrows). All of these findings were secondary to                     acute otomastoiditis. At 2 months after the myringotomy, right cortical                     mastoidectomy was performed. (c) Axial nonenhanced CT image shows the right                     cortical mastoidectomy (light brown arrows) and occupation of the remaining                     mastoid cells. Two months after the mastoidectomy, the ear secretion continued.                     (d, e) Axial contrast-enhanced CT image (d) and axial contrast-enhanced                     T1-weighted MR image (e) show an inflammatory process in the right                     posterolateral wall of the nasopharynx (pink arrows) with partial thrombosis of                     the right internal jugular vein (blue arrow in e) and clivus erosion (green                     arrows in d). The findings suggested SBO.

Figure 12b. Patient 4, a 74-year-old man with chronic suppurative otitis media who underwent right myringotomy, but the symptoms and headache persisted. (a) Coronal contrast-enhanced CT image shows opacification of the right middle ear and mastoid cells (orange arrows) and bone erosion of the right mastoid process (lavender arrow). The right stylomastoid foramen was expanded (green arrow). (b) Axial contrast-enhanced CT image shows an inflammatory area around the right mastoid process, with fat stranding (blue circle). There is sclerosis of the right maxillary sinus (green arrows). All of these findings were secondary to acute otomastoiditis. At 2 months after the myringotomy, right cortical mastoidectomy was performed. (c) Axial nonenhanced CT image shows the right cortical mastoidectomy (light brown arrows) and occupation of the remaining mastoid cells. Two months after the mastoidectomy, the ear secretion continued. (d, e) Axial contrast-enhanced CT image (d) and axial contrast-enhanced T1-weighted MR image (e) show an inflammatory process in the right posterolateral wall of the nasopharynx (pink arrows) with partial thrombosis of the right internal jugular vein (blue arrow in e) and clivus erosion (green arrows in d). The findings suggested SBO.

Patient 4, a 74-year-old man with chronic suppurative otitis media who                     underwent right myringotomy, but the symptoms and headache persisted. (a)                     Coronal contrast-enhanced CT image shows opacification of the right middle ear                     and mastoid cells (orange arrows) and bone erosion of the right mastoid process                     (lavender arrow). The right stylomastoid foramen was expanded (green arrow). (b)                     Axial contrast-enhanced CT image shows an inflammatory area around the right                     mastoid process, with fat stranding (blue circle). There is sclerosis of the                     right maxillary sinus (green arrows). All of these findings were secondary to                     acute otomastoiditis. At 2 months after the myringotomy, right cortical                     mastoidectomy was performed. (c) Axial nonenhanced CT image shows the right                     cortical mastoidectomy (light brown arrows) and occupation of the remaining                     mastoid cells. Two months after the mastoidectomy, the ear secretion continued.                     (d, e) Axial contrast-enhanced CT image (d) and axial contrast-enhanced                     T1-weighted MR image (e) show an inflammatory process in the right                     posterolateral wall of the nasopharynx (pink arrows) with partial thrombosis of                     the right internal jugular vein (blue arrow in e) and clivus erosion (green                     arrows in d). The findings suggested SBO.

Figure 12c. Patient 4, a 74-year-old man with chronic suppurative otitis media who underwent right myringotomy, but the symptoms and headache persisted. (a) Coronal contrast-enhanced CT image shows opacification of the right middle ear and mastoid cells (orange arrows) and bone erosion of the right mastoid process (lavender arrow). The right stylomastoid foramen was expanded (green arrow). (b) Axial contrast-enhanced CT image shows an inflammatory area around the right mastoid process, with fat stranding (blue circle). There is sclerosis of the right maxillary sinus (green arrows). All of these findings were secondary to acute otomastoiditis. At 2 months after the myringotomy, right cortical mastoidectomy was performed. (c) Axial nonenhanced CT image shows the right cortical mastoidectomy (light brown arrows) and occupation of the remaining mastoid cells. Two months after the mastoidectomy, the ear secretion continued. (d, e) Axial contrast-enhanced CT image (d) and axial contrast-enhanced T1-weighted MR image (e) show an inflammatory process in the right posterolateral wall of the nasopharynx (pink arrows) with partial thrombosis of the right internal jugular vein (blue arrow in e) and clivus erosion (green arrows in d). The findings suggested SBO.

Patient 4, a 74-year-old man with chronic suppurative otitis media who                     underwent right myringotomy, but the symptoms and headache persisted. (a)                     Coronal contrast-enhanced CT image shows opacification of the right middle ear                     and mastoid cells (orange arrows) and bone erosion of the right mastoid process                     (lavender arrow). The right stylomastoid foramen was expanded (green arrow). (b)                     Axial contrast-enhanced CT image shows an inflammatory area around the right                     mastoid process, with fat stranding (blue circle). There is sclerosis of the                     right maxillary sinus (green arrows). All of these findings were secondary to                     acute otomastoiditis. At 2 months after the myringotomy, right cortical                     mastoidectomy was performed. (c) Axial nonenhanced CT image shows the right                     cortical mastoidectomy (light brown arrows) and occupation of the remaining                     mastoid cells. Two months after the mastoidectomy, the ear secretion continued.                     (d, e) Axial contrast-enhanced CT image (d) and axial contrast-enhanced                     T1-weighted MR image (e) show an inflammatory process in the right                     posterolateral wall of the nasopharynx (pink arrows) with partial thrombosis of                     the right internal jugular vein (blue arrow in e) and clivus erosion (green                     arrows in d). The findings suggested SBO.

Figure 12d. Patient 4, a 74-year-old man with chronic suppurative otitis media who underwent right myringotomy, but the symptoms and headache persisted. (a) Coronal contrast-enhanced CT image shows opacification of the right middle ear and mastoid cells (orange arrows) and bone erosion of the right mastoid process (lavender arrow). The right stylomastoid foramen was expanded (green arrow). (b) Axial contrast-enhanced CT image shows an inflammatory area around the right mastoid process, with fat stranding (blue circle). There is sclerosis of the right maxillary sinus (green arrows). All of these findings were secondary to acute otomastoiditis. At 2 months after the myringotomy, right cortical mastoidectomy was performed. (c) Axial nonenhanced CT image shows the right cortical mastoidectomy (light brown arrows) and occupation of the remaining mastoid cells. Two months after the mastoidectomy, the ear secretion continued. (d, e) Axial contrast-enhanced CT image (d) and axial contrast-enhanced T1-weighted MR image (e) show an inflammatory process in the right posterolateral wall of the nasopharynx (pink arrows) with partial thrombosis of the right internal jugular vein (blue arrow in e) and clivus erosion (green arrows in d). The findings suggested SBO.

Patient 4, a 74-year-old man with chronic suppurative otitis media who                     underwent right myringotomy, but the symptoms and headache persisted. (a)                     Coronal contrast-enhanced CT image shows opacification of the right middle ear                     and mastoid cells (orange arrows) and bone erosion of the right mastoid process                     (lavender arrow). The right stylomastoid foramen was expanded (green arrow). (b)                     Axial contrast-enhanced CT image shows an inflammatory area around the right                     mastoid process, with fat stranding (blue circle). There is sclerosis of the                     right maxillary sinus (green arrows). All of these findings were secondary to                     acute otomastoiditis. At 2 months after the myringotomy, right cortical                     mastoidectomy was performed. (c) Axial nonenhanced CT image shows the right                     cortical mastoidectomy (light brown arrows) and occupation of the remaining                     mastoid cells. Two months after the mastoidectomy, the ear secretion continued.                     (d, e) Axial contrast-enhanced CT image (d) and axial contrast-enhanced                     T1-weighted MR image (e) show an inflammatory process in the right                     posterolateral wall of the nasopharynx (pink arrows) with partial thrombosis of                     the right internal jugular vein (blue arrow in e) and clivus erosion (green                     arrows in d). The findings suggested SBO.

Figure 12e. Patient 4, a 74-year-old man with chronic suppurative otitis media who underwent right myringotomy, but the symptoms and headache persisted. (a) Coronal contrast-enhanced CT image shows opacification of the right middle ear and mastoid cells (orange arrows) and bone erosion of the right mastoid process (lavender arrow). The right stylomastoid foramen was expanded (green arrow). (b) Axial contrast-enhanced CT image shows an inflammatory area around the right mastoid process, with fat stranding (blue circle). There is sclerosis of the right maxillary sinus (green arrows). All of these findings were secondary to acute otomastoiditis. At 2 months after the myringotomy, right cortical mastoidectomy was performed. (c) Axial nonenhanced CT image shows the right cortical mastoidectomy (light brown arrows) and occupation of the remaining mastoid cells. Two months after the mastoidectomy, the ear secretion continued. (d, e) Axial contrast-enhanced CT image (d) and axial contrast-enhanced T1-weighted MR image (e) show an inflammatory process in the right posterolateral wall of the nasopharynx (pink arrows) with partial thrombosis of the right internal jugular vein (blue arrow in e) and clivus erosion (green arrows in d). The findings suggested SBO.

Patient 5, a 71-year-old man with binocular diplopia, dysphagia, and                     dysphonia. Findings from a lumbar puncture demonstrated lymphocytic meningitis.                     (a, b) Axial contrast-enhanced CT images show bilateral opacification of mastoid                     cells (orange arrows in a), which is more extensive on the left side. The                     enhancing mass in the posterior wall of the nasopharynx (green arrows in b)                     extends to the clivus (green arrows in a) and both carotid spaces, with                     compression of the right jugular vein (blue dot in b). The lesion reaches the                     posterior fossa, where it appears as a soft-tissue mass in the prepontine                     cistern (pink arrows in a). (c) Sagittal contrast-enhanced T1-weighted MR image                     shows enhancement of the prevertebral space (brown arrows) and sphenoid bone                     (green arrows). Repeated biopsies were negative for malignancy. Two months                     later, the symptoms persisted. (d) Axial contrast-enhanced T1-weighted MR image                     shows an increased lesion size, with involvement of the masticator spaces (navy                     blue arrows) and enhancement of the clivus (green arrows) and both condyles                     (brown arrows). A partial thrombosis of the right sigmoid sinus (medium blue                     arrows) and bilateral otomastoiditis (yellow arrows) were also observed. (e)                     99mTc SPECT/CT image shows an increase in osteoblastic activity in the bilateral                     mastoid cells (arrow). The findings suggested SBO complicated by                     meningitis.

Figure 13a. Patient 5, a 71-year-old man with binocular diplopia, dysphagia, and dysphonia. Findings from a lumbar puncture demonstrated lymphocytic meningitis. (a, b) Axial contrast-enhanced CT images show bilateral opacification of mastoid cells (orange arrows in a), which is more extensive on the left side. The enhancing mass in the posterior wall of the nasopharynx (green arrows in b) extends to the clivus (green arrows in a) and both carotid spaces, with compression of the right jugular vein (blue dot in b). The lesion reaches the posterior fossa, where it appears as a soft-tissue mass in the prepontine cistern (pink arrows in a). (c) Sagittal contrast-enhanced T1-weighted MR image shows enhancement of the prevertebral space (brown arrows) and sphenoid bone (green arrows). Repeated biopsies were negative for malignancy. Two months later, the symptoms persisted. (d) Axial contrast-enhanced T1-weighted MR image shows an increased lesion size, with involvement of the masticator spaces (navy blue arrows) and enhancement of the clivus (green arrows) and both condyles (brown arrows). A partial thrombosis of the right sigmoid sinus (medium blue arrows) and bilateral otomastoiditis (yellow arrows) were also observed. (e) 99mTc SPECT/CT image shows an increase in osteoblastic activity in the bilateral mastoid cells (arrow). The findings suggested SBO complicated by meningitis.

Patient 5, a 71-year-old man with binocular diplopia, dysphagia, and                     dysphonia. Findings from a lumbar puncture demonstrated lymphocytic meningitis.                     (a, b) Axial contrast-enhanced CT images show bilateral opacification of mastoid                     cells (orange arrows in a), which is more extensive on the left side. The                     enhancing mass in the posterior wall of the nasopharynx (green arrows in b)                     extends to the clivus (green arrows in a) and both carotid spaces, with                     compression of the right jugular vein (blue dot in b). The lesion reaches the                     posterior fossa, where it appears as a soft-tissue mass in the prepontine                     cistern (pink arrows in a). (c) Sagittal contrast-enhanced T1-weighted MR image                     shows enhancement of the prevertebral space (brown arrows) and sphenoid bone                     (green arrows). Repeated biopsies were negative for malignancy. Two months                     later, the symptoms persisted. (d) Axial contrast-enhanced T1-weighted MR image                     shows an increased lesion size, with involvement of the masticator spaces (navy                     blue arrows) and enhancement of the clivus (green arrows) and both condyles                     (brown arrows). A partial thrombosis of the right sigmoid sinus (medium blue                     arrows) and bilateral otomastoiditis (yellow arrows) were also observed. (e)                     99mTc SPECT/CT image shows an increase in osteoblastic activity in the bilateral                     mastoid cells (arrow). The findings suggested SBO complicated by                     meningitis.

Figure 13b. Patient 5, a 71-year-old man with binocular diplopia, dysphagia, and dysphonia. Findings from a lumbar puncture demonstrated lymphocytic meningitis. (a, b) Axial contrast-enhanced CT images show bilateral opacification of mastoid cells (orange arrows in a), which is more extensive on the left side. The enhancing mass in the posterior wall of the nasopharynx (green arrows in b) extends to the clivus (green arrows in a) and both carotid spaces, with compression of the right jugular vein (blue dot in b). The lesion reaches the posterior fossa, where it appears as a soft-tissue mass in the prepontine cistern (pink arrows in a). (c) Sagittal contrast-enhanced T1-weighted MR image shows enhancement of the prevertebral space (brown arrows) and sphenoid bone (green arrows). Repeated biopsies were negative for malignancy. Two months later, the symptoms persisted. (d) Axial contrast-enhanced T1-weighted MR image shows an increased lesion size, with involvement of the masticator spaces (navy blue arrows) and enhancement of the clivus (green arrows) and both condyles (brown arrows). A partial thrombosis of the right sigmoid sinus (medium blue arrows) and bilateral otomastoiditis (yellow arrows) were also observed. (e) 99mTc SPECT/CT image shows an increase in osteoblastic activity in the bilateral mastoid cells (arrow). The findings suggested SBO complicated by meningitis.

Patient 5, a 71-year-old man with binocular diplopia, dysphagia, and                     dysphonia. Findings from a lumbar puncture demonstrated lymphocytic meningitis.                     (a, b) Axial contrast-enhanced CT images show bilateral opacification of mastoid                     cells (orange arrows in a), which is more extensive on the left side. The                     enhancing mass in the posterior wall of the nasopharynx (green arrows in b)                     extends to the clivus (green arrows in a) and both carotid spaces, with                     compression of the right jugular vein (blue dot in b). The lesion reaches the                     posterior fossa, where it appears as a soft-tissue mass in the prepontine                     cistern (pink arrows in a). (c) Sagittal contrast-enhanced T1-weighted MR image                     shows enhancement of the prevertebral space (brown arrows) and sphenoid bone                     (green arrows). Repeated biopsies were negative for malignancy. Two months                     later, the symptoms persisted. (d) Axial contrast-enhanced T1-weighted MR image                     shows an increased lesion size, with involvement of the masticator spaces (navy                     blue arrows) and enhancement of the clivus (green arrows) and both condyles                     (brown arrows). A partial thrombosis of the right sigmoid sinus (medium blue                     arrows) and bilateral otomastoiditis (yellow arrows) were also observed. (e)                     99mTc SPECT/CT image shows an increase in osteoblastic activity in the bilateral                     mastoid cells (arrow). The findings suggested SBO complicated by                     meningitis.

Figure 13c. Patient 5, a 71-year-old man with binocular diplopia, dysphagia, and dysphonia. Findings from a lumbar puncture demonstrated lymphocytic meningitis. (a, b) Axial contrast-enhanced CT images show bilateral opacification of mastoid cells (orange arrows in a), which is more extensive on the left side. The enhancing mass in the posterior wall of the nasopharynx (green arrows in b) extends to the clivus (green arrows in a) and both carotid spaces, with compression of the right jugular vein (blue dot in b). The lesion reaches the posterior fossa, where it appears as a soft-tissue mass in the prepontine cistern (pink arrows in a). (c) Sagittal contrast-enhanced T1-weighted MR image shows enhancement of the prevertebral space (brown arrows) and sphenoid bone (green arrows). Repeated biopsies were negative for malignancy. Two months later, the symptoms persisted. (d) Axial contrast-enhanced T1-weighted MR image shows an increased lesion size, with involvement of the masticator spaces (navy blue arrows) and enhancement of the clivus (green arrows) and both condyles (brown arrows). A partial thrombosis of the right sigmoid sinus (medium blue arrows) and bilateral otomastoiditis (yellow arrows) were also observed. (e) 99mTc SPECT/CT image shows an increase in osteoblastic activity in the bilateral mastoid cells (arrow). The findings suggested SBO complicated by meningitis.

Patient 5, a 71-year-old man with binocular diplopia, dysphagia, and                     dysphonia. Findings from a lumbar puncture demonstrated lymphocytic meningitis.                     (a, b) Axial contrast-enhanced CT images show bilateral opacification of mastoid                     cells (orange arrows in a), which is more extensive on the left side. The                     enhancing mass in the posterior wall of the nasopharynx (green arrows in b)                     extends to the clivus (green arrows in a) and both carotid spaces, with                     compression of the right jugular vein (blue dot in b). The lesion reaches the                     posterior fossa, where it appears as a soft-tissue mass in the prepontine                     cistern (pink arrows in a). (c) Sagittal contrast-enhanced T1-weighted MR image                     shows enhancement of the prevertebral space (brown arrows) and sphenoid bone                     (green arrows). Repeated biopsies were negative for malignancy. Two months                     later, the symptoms persisted. (d) Axial contrast-enhanced T1-weighted MR image                     shows an increased lesion size, with involvement of the masticator spaces (navy                     blue arrows) and enhancement of the clivus (green arrows) and both condyles                     (brown arrows). A partial thrombosis of the right sigmoid sinus (medium blue                     arrows) and bilateral otomastoiditis (yellow arrows) were also observed. (e)                     99mTc SPECT/CT image shows an increase in osteoblastic activity in the bilateral                     mastoid cells (arrow). The findings suggested SBO complicated by                     meningitis.

Figure 13d. Patient 5, a 71-year-old man with binocular diplopia, dysphagia, and dysphonia. Findings from a lumbar puncture demonstrated lymphocytic meningitis. (a, b) Axial contrast-enhanced CT images show bilateral opacification of mastoid cells (orange arrows in a), which is more extensive on the left side. The enhancing mass in the posterior wall of the nasopharynx (green arrows in b) extends to the clivus (green arrows in a) and both carotid spaces, with compression of the right jugular vein (blue dot in b). The lesion reaches the posterior fossa, where it appears as a soft-tissue mass in the prepontine cistern (pink arrows in a). (c) Sagittal contrast-enhanced T1-weighted MR image shows enhancement of the prevertebral space (brown arrows) and sphenoid bone (green arrows). Repeated biopsies were negative for malignancy. Two months later, the symptoms persisted. (d) Axial contrast-enhanced T1-weighted MR image shows an increased lesion size, with involvement of the masticator spaces (navy blue arrows) and enhancement of the clivus (green arrows) and both condyles (brown arrows). A partial thrombosis of the right sigmoid sinus (medium blue arrows) and bilateral otomastoiditis (yellow arrows) were also observed. (e) 99mTc SPECT/CT image shows an increase in osteoblastic activity in the bilateral mastoid cells (arrow). The findings suggested SBO complicated by meningitis.

Patient 5, a 71-year-old man with binocular diplopia, dysphagia, and                     dysphonia. Findings from a lumbar puncture demonstrated lymphocytic meningitis.                     (a, b) Axial contrast-enhanced CT images show bilateral opacification of mastoid                     cells (orange arrows in a), which is more extensive on the left side. The                     enhancing mass in the posterior wall of the nasopharynx (green arrows in b)                     extends to the clivus (green arrows in a) and both carotid spaces, with                     compression of the right jugular vein (blue dot in b). The lesion reaches the                     posterior fossa, where it appears as a soft-tissue mass in the prepontine                     cistern (pink arrows in a). (c) Sagittal contrast-enhanced T1-weighted MR image                     shows enhancement of the prevertebral space (brown arrows) and sphenoid bone                     (green arrows). Repeated biopsies were negative for malignancy. Two months                     later, the symptoms persisted. (d) Axial contrast-enhanced T1-weighted MR image                     shows an increased lesion size, with involvement of the masticator spaces (navy                     blue arrows) and enhancement of the clivus (green arrows) and both condyles                     (brown arrows). A partial thrombosis of the right sigmoid sinus (medium blue                     arrows) and bilateral otomastoiditis (yellow arrows) were also observed. (e)                     99mTc SPECT/CT image shows an increase in osteoblastic activity in the bilateral                     mastoid cells (arrow). The findings suggested SBO complicated by                     meningitis.

Figure 13e. Patient 5, a 71-year-old man with binocular diplopia, dysphagia, and dysphonia. Findings from a lumbar puncture demonstrated lymphocytic meningitis. (a, b) Axial contrast-enhanced CT images show bilateral opacification of mastoid cells (orange arrows in a), which is more extensive on the left side. The enhancing mass in the posterior wall of the nasopharynx (green arrows in b) extends to the clivus (green arrows in a) and both carotid spaces, with compression of the right jugular vein (blue dot in b). The lesion reaches the posterior fossa, where it appears as a soft-tissue mass in the prepontine cistern (pink arrows in a). (c) Sagittal contrast-enhanced T1-weighted MR image shows enhancement of the prevertebral space (brown arrows) and sphenoid bone (green arrows). Repeated biopsies were negative for malignancy. Two months later, the symptoms persisted. (d) Axial contrast-enhanced T1-weighted MR image shows an increased lesion size, with involvement of the masticator spaces (navy blue arrows) and enhancement of the clivus (green arrows) and both condyles (brown arrows). A partial thrombosis of the right sigmoid sinus (medium blue arrows) and bilateral otomastoiditis (yellow arrows) were also observed. (e) 99mTc SPECT/CT image shows an increase in osteoblastic activity in the bilateral mastoid cells (arrow). The findings suggested SBO complicated by meningitis.

Patient 6, a 76-year-old man with non-Hodgkin lymphoma who had a complete                     response to treatment with rituximab, fludarabine, and ciclofosfamide. At the                     time when the SBO occurred, the patient was in maintenance with monoclonal                     anti-CD20 antibody therapy and had left external otitis for 3 months without                     improvement after topical and oral therapy. 99mTc SPECT/CT (not shown) showed                     increased osteoblastic activity in the left temporal bone, probably secondary to                     malignant external otitis. Five months later, the symptoms persisted and the                     patient started to experience diplopia. (a, b) Axial (a) and coronal (b)                     nonenhanced CT images show left mastoid sclerosis (pink arrows in a) and                     opacification of both middle ears (purple arrows in b), which is secondary to                     chronic otomastoiditis; clivus bone erosion (green arrows); and left foramen                     lacerum enlargement (brown arrow in b). (c) 99mTc SPECT/CT image from a repeat                     examination shows increased uptake in the clivus, which is more substantial in                     the left lateral margin. (d) Axial contrast-enhanced T1-weighted MR image shows                     an enhancing mass in the posterior wall of the nasopharynx around the clivus and                     both carotid spaces (orange arrows); bone enhancement of the clivus (yellow                     arrows) and occipital condyles; dural enhancement (light green arrows); and                     thrombosis of the left sigmoid sinus (blue arrows). The findings suggested                     SBO.

Figure 14a. Patient 6, a 76-year-old man with non-Hodgkin lymphoma who had a complete response to treatment with rituximab, fludarabine, and ciclofosfamide. At the time when the SBO occurred, the patient was in maintenance with monoclonal anti-CD20 antibody therapy and had left external otitis for 3 months without improvement after topical and oral therapy. 99mTc SPECT/CT (not shown) showed increased osteoblastic activity in the left temporal bone, probably secondary to malignant external otitis. Five months later, the symptoms persisted and the patient started to experience diplopia. (a, b) Axial (a) and coronal (b) nonenhanced CT images show left mastoid sclerosis (pink arrows in a) and opacification of both middle ears (purple arrows in b), which is secondary to chronic otomastoiditis; clivus bone erosion (green arrows); and left foramen lacerum enlargement (brown arrow in b). (c) 99mTc SPECT/CT image from a repeat examination shows increased uptake in the clivus, which is more substantial in the left lateral margin. (d) Axial contrast-enhanced T1-weighted MR image shows an enhancing mass in the posterior wall of the nasopharynx around the clivus and both carotid spaces (orange arrows); bone enhancement of the clivus (yellow arrows) and occipital condyles; dural enhancement (light green arrows); and thrombosis of the left sigmoid sinus (blue arrows). The findings suggested SBO.

Patient 6, a 76-year-old man with non-Hodgkin lymphoma who had a complete                     response to treatment with rituximab, fludarabine, and ciclofosfamide. At the                     time when the SBO occurred, the patient was in maintenance with monoclonal                     anti-CD20 antibody therapy and had left external otitis for 3 months without                     improvement after topical and oral therapy. 99mTc SPECT/CT (not shown) showed                     increased osteoblastic activity in the left temporal bone, probably secondary to                     malignant external otitis. Five months later, the symptoms persisted and the                     patient started to experience diplopia. (a, b) Axial (a) and coronal (b)                     nonenhanced CT images show left mastoid sclerosis (pink arrows in a) and                     opacification of both middle ears (purple arrows in b), which is secondary to                     chronic otomastoiditis; clivus bone erosion (green arrows); and left foramen                     lacerum enlargement (brown arrow in b). (c) 99mTc SPECT/CT image from a repeat                     examination shows increased uptake in the clivus, which is more substantial in                     the left lateral margin. (d) Axial contrast-enhanced T1-weighted MR image shows                     an enhancing mass in the posterior wall of the nasopharynx around the clivus and                     both carotid spaces (orange arrows); bone enhancement of the clivus (yellow                     arrows) and occipital condyles; dural enhancement (light green arrows); and                     thrombosis of the left sigmoid sinus (blue arrows). The findings suggested                     SBO.

Figure 14b. Patient 6, a 76-year-old man with non-Hodgkin lymphoma who had a complete response to treatment with rituximab, fludarabine, and ciclofosfamide. At the time when the SBO occurred, the patient was in maintenance with monoclonal anti-CD20 antibody therapy and had left external otitis for 3 months without improvement after topical and oral therapy. 99mTc SPECT/CT (not shown) showed increased osteoblastic activity in the left temporal bone, probably secondary to malignant external otitis. Five months later, the symptoms persisted and the patient started to experience diplopia. (a, b) Axial (a) and coronal (b) nonenhanced CT images show left mastoid sclerosis (pink arrows in a) and opacification of both middle ears (purple arrows in b), which is secondary to chronic otomastoiditis; clivus bone erosion (green arrows); and left foramen lacerum enlargement (brown arrow in b). (c) 99mTc SPECT/CT image from a repeat examination shows increased uptake in the clivus, which is more substantial in the left lateral margin. (d) Axial contrast-enhanced T1-weighted MR image shows an enhancing mass in the posterior wall of the nasopharynx around the clivus and both carotid spaces (orange arrows); bone enhancement of the clivus (yellow arrows) and occipital condyles; dural enhancement (light green arrows); and thrombosis of the left sigmoid sinus (blue arrows). The findings suggested SBO.

Patient 6, a 76-year-old man with non-Hodgkin lymphoma who had a complete                     response to treatment with rituximab, fludarabine, and ciclofosfamide. At the                     time when the SBO occurred, the patient was in maintenance with monoclonal                     anti-CD20 antibody therapy and had left external otitis for 3 months without                     improvement after topical and oral therapy. 99mTc SPECT/CT (not shown) showed                     increased osteoblastic activity in the left temporal bone, probably secondary to                     malignant external otitis. Five months later, the symptoms persisted and the                     patient started to experience diplopia. (a, b) Axial (a) and coronal (b)                     nonenhanced CT images show left mastoid sclerosis (pink arrows in a) and                     opacification of both middle ears (purple arrows in b), which is secondary to                     chronic otomastoiditis; clivus bone erosion (green arrows); and left foramen                     lacerum enlargement (brown arrow in b). (c) 99mTc SPECT/CT image from a repeat                     examination shows increased uptake in the clivus, which is more substantial in                     the left lateral margin. (d) Axial contrast-enhanced T1-weighted MR image shows                     an enhancing mass in the posterior wall of the nasopharynx around the clivus and                     both carotid spaces (orange arrows); bone enhancement of the clivus (yellow                     arrows) and occipital condyles; dural enhancement (light green arrows); and                     thrombosis of the left sigmoid sinus (blue arrows). The findings suggested                     SBO.

Figure 14c. Patient 6, a 76-year-old man with non-Hodgkin lymphoma who had a complete response to treatment with rituximab, fludarabine, and ciclofosfamide. At the time when the SBO occurred, the patient was in maintenance with monoclonal anti-CD20 antibody therapy and had left external otitis for 3 months without improvement after topical and oral therapy. 99mTc SPECT/CT (not shown) showed increased osteoblastic activity in the left temporal bone, probably secondary to malignant external otitis. Five months later, the symptoms persisted and the patient started to experience diplopia. (a, b) Axial (a) and coronal (b) nonenhanced CT images show left mastoid sclerosis (pink arrows in a) and opacification of both middle ears (purple arrows in b), which is secondary to chronic otomastoiditis; clivus bone erosion (green arrows); and left foramen lacerum enlargement (brown arrow in b). (c) 99mTc SPECT/CT image from a repeat examination shows increased uptake in the clivus, which is more substantial in the left lateral margin. (d) Axial contrast-enhanced T1-weighted MR image shows an enhancing mass in the posterior wall of the nasopharynx around the clivus and both carotid spaces (orange arrows); bone enhancement of the clivus (yellow arrows) and occipital condyles; dural enhancement (light green arrows); and thrombosis of the left sigmoid sinus (blue arrows). The findings suggested SBO.

Patient 6, a 76-year-old man with non-Hodgkin lymphoma who had a complete                     response to treatment with rituximab, fludarabine, and ciclofosfamide. At the                     time when the SBO occurred, the patient was in maintenance with monoclonal                     anti-CD20 antibody therapy and had left external otitis for 3 months without                     improvement after topical and oral therapy. 99mTc SPECT/CT (not shown) showed                     increased osteoblastic activity in the left temporal bone, probably secondary to                     malignant external otitis. Five months later, the symptoms persisted and the                     patient started to experience diplopia. (a, b) Axial (a) and coronal (b)                     nonenhanced CT images show left mastoid sclerosis (pink arrows in a) and                     opacification of both middle ears (purple arrows in b), which is secondary to                     chronic otomastoiditis; clivus bone erosion (green arrows); and left foramen                     lacerum enlargement (brown arrow in b). (c) 99mTc SPECT/CT image from a repeat                     examination shows increased uptake in the clivus, which is more substantial in                     the left lateral margin. (d) Axial contrast-enhanced T1-weighted MR image shows                     an enhancing mass in the posterior wall of the nasopharynx around the clivus and                     both carotid spaces (orange arrows); bone enhancement of the clivus (yellow                     arrows) and occipital condyles; dural enhancement (light green arrows); and                     thrombosis of the left sigmoid sinus (blue arrows). The findings suggested                     SBO.

Figure 14d. Patient 6, a 76-year-old man with non-Hodgkin lymphoma who had a complete response to treatment with rituximab, fludarabine, and ciclofosfamide. At the time when the SBO occurred, the patient was in maintenance with monoclonal anti-CD20 antibody therapy and had left external otitis for 3 months without improvement after topical and oral therapy. 99mTc SPECT/CT (not shown) showed increased osteoblastic activity in the left temporal bone, probably secondary to malignant external otitis. Five months later, the symptoms persisted and the patient started to experience diplopia. (a, b) Axial (a) and coronal (b) nonenhanced CT images show left mastoid sclerosis (pink arrows in a) and opacification of both middle ears (purple arrows in b), which is secondary to chronic otomastoiditis; clivus bone erosion (green arrows); and left foramen lacerum enlargement (brown arrow in b). (c) 99mTc SPECT/CT image from a repeat examination shows increased uptake in the clivus, which is more substantial in the left lateral margin. (d) Axial contrast-enhanced T1-weighted MR image shows an enhancing mass in the posterior wall of the nasopharynx around the clivus and both carotid spaces (orange arrows); bone enhancement of the clivus (yellow arrows) and occipital condyles; dural enhancement (light green arrows); and thrombosis of the left sigmoid sinus (blue arrows). The findings suggested SBO.

SBO findings are nonspecific and mimic malignancy. CT is the best option for evaluating bone erosion and demineralization, while nonenhanced CT can be helpful in emergencies. CT can show erosion of the bone margins (Figs 6a, 7c, 10a, 13a, 14a, 14b) or opacification of the middle ear and mastoid cells due to eustachian tube dysfunction (Figs 7d, 10a, 12d, 13a, 14a, 14b). Furthermore, contrast-enhanced CT can show diffuse soft-tissue swelling, obliteration of normal fat planes, involvement of the skull base foramina, and vascular complications (Figs 7a, 7b, 9a, 10b, 12d, 13b) (7,12).

MRI is useful for evaluating the anatomic location and extent of the infection. In patients with SBO, MRI can show an enhancing soft-tissue mass with an infiltrating pattern (at contrast-enhanced T1-weighted MRI), bone marrow infiltration (hypointensity at T1-weighted MRI and hyperintensity and contrast enhancement at T2-weighted MRI), adjacent soft-tissue edema (elevated signal intensity and contrast enhancement at T2-weighted MRI), effacement of fat planes, intracranial and perineural extension, and the involvement of lateral structures (parotid gland, temporomandibular joint) (Figs 6b, 8c, 10c, 10d, 11a, 11b, 12e, 13c, 13d, 14d) (1,12,13).

The inflammatory process usually shows restricted diffusion, with high signal intensity at diffusion-weighted MRI and low signal intensity on apparent diffusion coefficient (ADC) maps. Several authors (1416) have stated that the ADCs in patients with SBO are higher than those in patients with malignant neoplastic processes. Furthermore, diffusion is useful for the detection of the formation of abscesses, which supports the diagnosis of SBO (Fig 8d).

Repeated CT or MRI examinations are helpful during follow-up to assess treatment response and detect complications (1,8).

Nuclear imaging can help to confirm bone involvement with high sensitivity. There are several techniques, which can be classified into two groups: gamma tracers and β-emitting tracers. The first group includes technetium 99m (99mTc) methylene diphosphonate bone scintigraphy and SPECT/CT. The radiotracer accumulates in sites of increased osteoblastic activity and is therefore useful for confirming the diagnosis (Figs 6c, 11c, 13e, 14c). Another technique is gallium 67 (67Ga) scintigraphy, which reveals active infection by binding to dividing cells (leukocytes in infectious processes) and is employed to monitor the response. The β-emitting group includes fluorodeoxyglucose and sodium fluoride; the former allows detection of increased metabolism in patients with infection, whereas the latter provides information about increased bone turnover (5,7,12,17).

Complications

Infection can be complicated by the formation of abscesses in contiguous soft tissues (Fig 8c, 8d) (13). At MRI, abscesses can be visualized as areas of liquid signal intensity with diffusion restriction and peripheral enhancement. The sequences with fat suppression and contrast enhancement can help to differentiate phlegmons (enhancement of soft tissues) from soft-issue abscesses (ring enhancement and central necrotic area). Periosteal displacement can be secondary to the formation of subperiosteal abscesses.

Adjacent vascular structures may also be affected, causing venous sinus thrombosis (Figs 11b, 12d, 12e, 13d, 14d), arterial pseudoaneurysms (Figs 6d, 8c, 9a, 9b, 9c), or ischemic infarction (5).

Venous sinus thrombosis can be detected at nonenhanced CT as a homogeneous hyperattenuation (50–80 HU) of the affected sinus (corresponding to a fresh thrombus) and at MRI by the absence of normal flow artifacts. Caution is advised, because false-positive results for artifacts can occur, resulting in a slow venous flow. Confirmation of venous sinus thrombosis is performed with contrast-enhanced CT and MRI, which show contrast filling defects (empty δ sign), usually accompanied by venous ectasia and dilated medullary venous structures. The process can spread and affect more than one venous sinus or even produce areas of cerebral venous infarctions, which can be identified by their atypical arterial distribution (18).

Arterial adventitial infections can cause transmural dissection, which leads to the formation of a blood collection between the outer arterial layers, causing a mycotic pseudoaneurysm. One of the symptoms of this condition is bloody discharge from the ears or nose. The pseudoaneurysm is visualized at contrast-enhanced imaging as an enhancing saccular formation adjacent to an artery. Contrast-enhanced CT during the arterial phase allows confirmation of the communication of the saccular formation with the vessel’s lumen. Angiography is the standard diagnostic method for pseudoaneurysm and is useful for its treatment (19,20).

Another complication of arterial involvement of infection is ischemic infarction, and it should be suspected in patients with a sudden-onset focal neurologic deficit.

Intracranial spread can occur from extension through the petroclival synchondrosis, so meningitis, encephalitis, and even an intracranial abscess might develop (5).

In patients with meningitis, the symptoms are fever, headache, neck stiffness, and an altered level of consciousness. Contrast-enhanced CT and MR images show leptomeningeal and pachymeningeal enhancement. A purulent exudate can be formed in the subarachnoid space, with higher attenuation at nonenhanced CT and an incomplete suppression of the cerebrospinal fluid signal intensity at fluid-attenuated inversion-recovery MRI and restricted diffusion at MRI. When patients are suspected to have meningitis, the diagnosis should be confirmed with lumbar puncture (21).

Intracranial abscesses including epidural abscesses, subdural empyemas, and intraparenchymal abscesses appear similar to purulent collections, with peripheral enhancement and diffusion restriction, associated surrounding edema, and mass effect (21).

Diagnosis of SBO

Teaching Point The diagnosis of SBO is usually delayed. In our study, the mean time from the onset of symptoms to diagnosis was 6 months, owing to the nonspecific symptoms of SBO, its long clinical course, and the fact that it mimics malignancies on radiologic images. The diagnosis of SBO should be based on four points: a high index of clinical suspicion, radiologic evidence of infection, repeated biopsy results that are negative for malignancy, and positive microbiologic isolation
.

High Index of Clinical Suspicion

The typical patient is an elderly man with diabetes and recurrent otitis externa (1). In this context, laboratory findings with an increased erythrocyte sedimentation rate, elevated C-reactive protein levels, and leukocytosis help raise the index of clinical suspicion (11).

Radiologic Evidence of Infection

When a radiologist is faced with an aggressive skull base process, especially in a typical patient, it is essential to consider SBO. The most frequent finding is a poorly defined enhancing mass in the posterior wall of the nasopharynx, with otomastoiditis, bone erosion, and enhancement. Adjacent soft-tissue enhancement is usually observed, without architectural distortion and with preservation of the smooth nasopharyngeal mucosa. The lesion can involve lateral structures such as the parotid gland and the temporomandibular joint (3,13).

Repeated Biopsies Negative for Malignancy

Given the radiologic findings, a biopsy is always necessary to differentiate SBO from malignancy. It is important to consider the possibility of SBO before performing the biopsy to maximize its potential yield. Repeated biopsies of the process will show acute or subacute inflammatory granulation tissue and nonspecific inflammatory changes and rule out malignancy (1,7).

Microbiologic Evaluation

The detection of microorganisms in biopsied bone or soft tissue is not always possible; however, microbiologic isolation of a causative pathogen allows confirmation of the diagnosis (1,2).

Differential Diagnosis

There are several neoplastic and inflammatory diseases that can mimic the imaging findings of SBO.

Neoplastic Processes

Nasopharyngeal Carcinoma.Nasopharyngeal carcinoma (NPC) is the most common primary malignancy of the nasopharynx. Patients can develop local symptoms such as epistaxis, conductive hearing loss, nasal obstruction, otalgia, headache, and cranial nerve involvement. However, patients often present late in the course of the disease, with cervical nodal or distant metastasis, in many cases (22) (Figs 1517).

Nasopharyngeal carcinoma in a 39-year-old woman with chronic                         suppurative otitis media who presented with a headache, diplopia, and                         lingual paresthesias. Axial contrast-enhanced CT image shows an enhancing                         mass (orange arrows) on the posterolateral wall of the nasopharynx. This                         lesion is very similar to the lesion in Figure 7a. The diagnosis was                         nonkeratinizing squamous cell carcinoma.

Figure 15. Nasopharyngeal carcinoma in a 39-year-old woman with chronic suppurative otitis media who presented with a headache, diplopia, and lingual paresthesias. Axial contrast-enhanced CT image shows an enhancing mass (orange arrows) on the posterolateral wall of the nasopharynx. This lesion is very similar to the lesion in Figure 7a. The diagnosis was nonkeratinizing squamous cell carcinoma.

Nasopharyngeal carcinoma in a 63-year-old man with a headache,                         diplopia, dysphagia, and hearing loss. (a) Axial contrast-enhanced CT image                         shows an enhancing mass in the nasopharynx with destruction of the clivus                         and the body of the sphenoid and erosion of the greater wings, the pterygoid                         process of the sphenoid bone, and the bilateral petrous bone (green arrows),                         with opacification of mastoid cells (orange arrows). (b) Sagittal                         contrast-enhanced T1-weighted MR image shows an enhancing mass with bone                         infiltration (green arrows) that extends into the prevertebral space (blue                         arrows) (c, d) Axial diffusion-weighted MR image (c) and ADC map (d) show                         restricted diffusion with high-signal-intensity foci at diffusion-weighted                         MRI and low signal intensity on the ADC map (arrows). The diagnosis was                         keratinizing squamous cell carcinoma.

Figure 16a. Nasopharyngeal carcinoma in a 63-year-old man with a headache, diplopia, dysphagia, and hearing loss. (a) Axial contrast-enhanced CT image shows an enhancing mass in the nasopharynx with destruction of the clivus and the body of the sphenoid and erosion of the greater wings, the pterygoid process of the sphenoid bone, and the bilateral petrous bone (green arrows), with opacification of mastoid cells (orange arrows). (b) Sagittal contrast-enhanced T1-weighted MR image shows an enhancing mass with bone infiltration (green arrows) that extends into the prevertebral space (blue arrows) (c, d) Axial diffusion-weighted MR image (c) and ADC map (d) show restricted diffusion with high-signal-intensity foci at diffusion-weighted MRI and low signal intensity on the ADC map (arrows). The diagnosis was keratinizing squamous cell carcinoma.

Nasopharyngeal carcinoma in a 63-year-old man with a headache,                         diplopia, dysphagia, and hearing loss. (a) Axial contrast-enhanced CT image                         shows an enhancing mass in the nasopharynx with destruction of the clivus                         and the body of the sphenoid and erosion of the greater wings, the pterygoid                         process of the sphenoid bone, and the bilateral petrous bone (green arrows),                         with opacification of mastoid cells (orange arrows). (b) Sagittal                         contrast-enhanced T1-weighted MR image shows an enhancing mass with bone                         infiltration (green arrows) that extends into the prevertebral space (blue                         arrows) (c, d) Axial diffusion-weighted MR image (c) and ADC map (d) show                         restricted diffusion with high-signal-intensity foci at diffusion-weighted                         MRI and low signal intensity on the ADC map (arrows). The diagnosis was                         keratinizing squamous cell carcinoma.

Figure 16b. Nasopharyngeal carcinoma in a 63-year-old man with a headache, diplopia, dysphagia, and hearing loss. (a) Axial contrast-enhanced CT image shows an enhancing mass in the nasopharynx with destruction of the clivus and the body of the sphenoid and erosion of the greater wings, the pterygoid process of the sphenoid bone, and the bilateral petrous bone (green arrows), with opacification of mastoid cells (orange arrows). (b) Sagittal contrast-enhanced T1-weighted MR image shows an enhancing mass with bone infiltration (green arrows) that extends into the prevertebral space (blue arrows) (c, d) Axial diffusion-weighted MR image (c) and ADC map (d) show restricted diffusion with high-signal-intensity foci at diffusion-weighted MRI and low signal intensity on the ADC map (arrows). The diagnosis was keratinizing squamous cell carcinoma.

Nasopharyngeal carcinoma in a 63-year-old man with a headache,                         diplopia, dysphagia, and hearing loss. (a) Axial contrast-enhanced CT image                         shows an enhancing mass in the nasopharynx with destruction of the clivus                         and the body of the sphenoid and erosion of the greater wings, the pterygoid                         process of the sphenoid bone, and the bilateral petrous bone (green arrows),                         with opacification of mastoid cells (orange arrows). (b) Sagittal                         contrast-enhanced T1-weighted MR image shows an enhancing mass with bone                         infiltration (green arrows) that extends into the prevertebral space (blue                         arrows) (c, d) Axial diffusion-weighted MR image (c) and ADC map (d) show                         restricted diffusion with high-signal-intensity foci at diffusion-weighted                         MRI and low signal intensity on the ADC map (arrows). The diagnosis was                         keratinizing squamous cell carcinoma.

Figure 16c. Nasopharyngeal carcinoma in a 63-year-old man with a headache, diplopia, dysphagia, and hearing loss. (a) Axial contrast-enhanced CT image shows an enhancing mass in the nasopharynx with destruction of the clivus and the body of the sphenoid and erosion of the greater wings, the pterygoid process of the sphenoid bone, and the bilateral petrous bone (green arrows), with opacification of mastoid cells (orange arrows). (b) Sagittal contrast-enhanced T1-weighted MR image shows an enhancing mass with bone infiltration (green arrows) that extends into the prevertebral space (blue arrows) (c, d) Axial diffusion-weighted MR image (c) and ADC map (d) show restricted diffusion with high-signal-intensity foci at diffusion-weighted MRI and low signal intensity on the ADC map (arrows). The diagnosis was keratinizing squamous cell carcinoma.

Nasopharyngeal carcinoma in a 63-year-old man with a headache,                         diplopia, dysphagia, and hearing loss. (a) Axial contrast-enhanced CT image                         shows an enhancing mass in the nasopharynx with destruction of the clivus                         and the body of the sphenoid and erosion of the greater wings, the pterygoid                         process of the sphenoid bone, and the bilateral petrous bone (green arrows),                         with opacification of mastoid cells (orange arrows). (b) Sagittal                         contrast-enhanced T1-weighted MR image shows an enhancing mass with bone                         infiltration (green arrows) that extends into the prevertebral space (blue                         arrows) (c, d) Axial diffusion-weighted MR image (c) and ADC map (d) show                         restricted diffusion with high-signal-intensity foci at diffusion-weighted                         MRI and low signal intensity on the ADC map (arrows). The diagnosis was                         keratinizing squamous cell carcinoma.

Figure 16d. Nasopharyngeal carcinoma in a 63-year-old man with a headache, diplopia, dysphagia, and hearing loss. (a) Axial contrast-enhanced CT image shows an enhancing mass in the nasopharynx with destruction of the clivus and the body of the sphenoid and erosion of the greater wings, the pterygoid process of the sphenoid bone, and the bilateral petrous bone (green arrows), with opacification of mastoid cells (orange arrows). (b) Sagittal contrast-enhanced T1-weighted MR image shows an enhancing mass with bone infiltration (green arrows) that extends into the prevertebral space (blue arrows) (c, d) Axial diffusion-weighted MR image (c) and ADC map (d) show restricted diffusion with high-signal-intensity foci at diffusion-weighted MRI and low signal intensity on the ADC map (arrows). The diagnosis was keratinizing squamous cell carcinoma.

Nasopharyngeal carcinoma in a 75-year-old man with diabetes mellitus                         and cranial nerve VI palsy who underwent an ear, nose, and throat                         examination, which revealed a probably malignant mucosal lesion. (a) Axial                         contrast-enhanced T1-weighted MR image shows an enhancing mass in the                         posterior wall of the nasopharynx (orange arrows) that extends into the                         masticator space, with infiltration of the lateral pterygoid muscle (green                         arrows), and surrounds the right internal carotid artery (red dot in a and                         b). (b) Axial contrast-enhanced T1-weighted MR image shows the mass                         extending into the middle cranial fossa (blue arrows) with thickening and                         enhancing of the meninges (yellow arrows) and sphenoid infiltration (pink                         arrows). (c, d) Axial diffusion-weighted MR image (c) and ADC map (d) show                         restricted diffusion. The mass shows high signal intensity on the                         diffusion-weighted MR image and low signal intensity on the ADC map (orange                         arrows). The diagnosis was lymphoepithelioma (nonkeratinizing squamous cell                         carcinoma with Epstein-Barr virus infection).

Figure 17a. Nasopharyngeal carcinoma in a 75-year-old man with diabetes mellitus and cranial nerve VI palsy who underwent an ear, nose, and throat examination, which revealed a probably malignant mucosal lesion. (a) Axial contrast-enhanced T1-weighted MR image shows an enhancing mass in the posterior wall of the nasopharynx (orange arrows) that extends into the masticator space, with infiltration of the lateral pterygoid muscle (green arrows), and surrounds the right internal carotid artery (red dot in a and b). (b) Axial contrast-enhanced T1-weighted MR image shows the mass extending into the middle cranial fossa (blue arrows) with thickening and enhancing of the meninges (yellow arrows) and sphenoid infiltration (pink arrows). (c, d) Axial diffusion-weighted MR image (c) and ADC map (d) show restricted diffusion. The mass shows high signal intensity on the diffusion-weighted MR image and low signal intensity on the ADC map (orange arrows). The diagnosis was lymphoepithelioma (nonkeratinizing squamous cell carcinoma with Epstein-Barr virus infection).

Nasopharyngeal carcinoma in a 75-year-old man with diabetes mellitus                         and cranial nerve VI palsy who underwent an ear, nose, and throat                         examination, which revealed a probably malignant mucosal lesion. (a) Axial                         contrast-enhanced T1-weighted MR image shows an enhancing mass in the                         posterior wall of the nasopharynx (orange arrows) that extends into the                         masticator space, with infiltration of the lateral pterygoid muscle (green                         arrows), and surrounds the right internal carotid artery (red dot in a and                         b). (b) Axial contrast-enhanced T1-weighted MR image shows the mass                         extending into the middle cranial fossa (blue arrows) with thickening and                         enhancing of the meninges (yellow arrows) and sphenoid infiltration (pink                         arrows). (c, d) Axial diffusion-weighted MR image (c) and ADC map (d) show                         restricted diffusion. The mass shows high signal intensity on the                         diffusion-weighted MR image and low signal intensity on the ADC map (orange                         arrows). The diagnosis was lymphoepithelioma (nonkeratinizing squamous cell                         carcinoma with Epstein-Barr virus infection).

Figure 17b. Nasopharyngeal carcinoma in a 75-year-old man with diabetes mellitus and cranial nerve VI palsy who underwent an ear, nose, and throat examination, which revealed a probably malignant mucosal lesion. (a) Axial contrast-enhanced T1-weighted MR image shows an enhancing mass in the posterior wall of the nasopharynx (orange arrows) that extends into the masticator space, with infiltration of the lateral pterygoid muscle (green arrows), and surrounds the right internal carotid artery (red dot in a and b). (b) Axial contrast-enhanced T1-weighted MR image shows the mass extending into the middle cranial fossa (blue arrows) with thickening and enhancing of the meninges (yellow arrows) and sphenoid infiltration (pink arrows). (c, d) Axial diffusion-weighted MR image (c) and ADC map (d) show restricted diffusion. The mass shows high signal intensity on the diffusion-weighted MR image and low signal intensity on the ADC map (orange arrows). The diagnosis was lymphoepithelioma (nonkeratinizing squamous cell carcinoma with Epstein-Barr virus infection).

Nasopharyngeal carcinoma in a 75-year-old man with diabetes mellitus                         and cranial nerve VI palsy who underwent an ear, nose, and throat                         examination, which revealed a probably malignant mucosal lesion. (a) Axial                         contrast-enhanced T1-weighted MR image shows an enhancing mass in the                         posterior wall of the nasopharynx (orange arrows) that extends into the                         masticator space, with infiltration of the lateral pterygoid muscle (green                         arrows), and surrounds the right internal carotid artery (red dot in a and                         b). (b) Axial contrast-enhanced T1-weighted MR image shows the mass                         extending into the middle cranial fossa (blue arrows) with thickening and                         enhancing of the meninges (yellow arrows) and sphenoid infiltration (pink                         arrows). (c, d) Axial diffusion-weighted MR image (c) and ADC map (d) show                         restricted diffusion. The mass shows high signal intensity on the                         diffusion-weighted MR image and low signal intensity on the ADC map (orange                         arrows). The diagnosis was lymphoepithelioma (nonkeratinizing squamous cell                         carcinoma with Epstein-Barr virus infection).

Figure 17c. Nasopharyngeal carcinoma in a 75-year-old man with diabetes mellitus and cranial nerve VI palsy who underwent an ear, nose, and throat examination, which revealed a probably malignant mucosal lesion. (a) Axial contrast-enhanced T1-weighted MR image shows an enhancing mass in the posterior wall of the nasopharynx (orange arrows) that extends into the masticator space, with infiltration of the lateral pterygoid muscle (green arrows), and surrounds the right internal carotid artery (red dot in a and b). (b) Axial contrast-enhanced T1-weighted MR image shows the mass extending into the middle cranial fossa (blue arrows) with thickening and enhancing of the meninges (yellow arrows) and sphenoid infiltration (pink arrows). (c, d) Axial diffusion-weighted MR image (c) and ADC map (d) show restricted diffusion. The mass shows high signal intensity on the diffusion-weighted MR image and low signal intensity on the ADC map (orange arrows). The diagnosis was lymphoepithelioma (nonkeratinizing squamous cell carcinoma with Epstein-Barr virus infection).

Nasopharyngeal carcinoma in a 75-year-old man with diabetes mellitus                         and cranial nerve VI palsy who underwent an ear, nose, and throat                         examination, which revealed a probably malignant mucosal lesion. (a) Axial                         contrast-enhanced T1-weighted MR image shows an enhancing mass in the                         posterior wall of the nasopharynx (orange arrows) that extends into the                         masticator space, with infiltration of the lateral pterygoid muscle (green                         arrows), and surrounds the right internal carotid artery (red dot in a and                         b). (b) Axial contrast-enhanced T1-weighted MR image shows the mass                         extending into the middle cranial fossa (blue arrows) with thickening and                         enhancing of the meninges (yellow arrows) and sphenoid infiltration (pink                         arrows). (c, d) Axial diffusion-weighted MR image (c) and ADC map (d) show                         restricted diffusion. The mass shows high signal intensity on the                         diffusion-weighted MR image and low signal intensity on the ADC map (orange                         arrows). The diagnosis was lymphoepithelioma (nonkeratinizing squamous cell                         carcinoma with Epstein-Barr virus infection).

Figure 17d. Nasopharyngeal carcinoma in a 75-year-old man with diabetes mellitus and cranial nerve VI palsy who underwent an ear, nose, and throat examination, which revealed a probably malignant mucosal lesion. (a) Axial contrast-enhanced T1-weighted MR image shows an enhancing mass in the posterior wall of the nasopharynx (orange arrows) that extends into the masticator space, with infiltration of the lateral pterygoid muscle (green arrows), and surrounds the right internal carotid artery (red dot in a and b). (b) Axial contrast-enhanced T1-weighted MR image shows the mass extending into the middle cranial fossa (blue arrows) with thickening and enhancing of the meninges (yellow arrows) and sphenoid infiltration (pink arrows). (c, d) Axial diffusion-weighted MR image (c) and ADC map (d) show restricted diffusion. The mass shows high signal intensity on the diffusion-weighted MR image and low signal intensity on the ADC map (orange arrows). The diagnosis was lymphoepithelioma (nonkeratinizing squamous cell carcinoma with Epstein-Barr virus infection).

Teaching Point NPC is the main diagnosis to consider in the differential diagnosis of SBO. Given that imaging does not allow differentiation of SBO from NPC, a biopsy is necessary. The imaging findings for these two entities are similar, with contrast-enhanced CT showing an enhancing mass with aggressive behavior, bone erosion, and opacification of mastoid cells (Figs 15, 16a). MRI also reveals an enhancing mass with bone infiltration (Figs 16b, 17a, 17b). Diffusion tends to be restricted, with low ADCs (Figs 16c, 16d, 17c, 17d) (14).

Teaching Point According to Goh et al (13), there are several characteristics of MRI examinations that can help in differentiation of these two diseases. Findings such as the involvement of lateral structures, soft-tissue enhancement, high signal intensity at T2-weighted MRI (edema), and abscess formation can lead to suspicion for SBO.
In comparison, architectural distortion, disrupted nasopharyngeal mucosa, and enlarged lymph nodes are more common in NPC (3,13).

Similarly, an ear, nose, and throat examination can help to guide the diagnosis. If the nasopharyngeal mucosa is normal, the likelihood of NPC decreases compared with that of SBO. In any case, a biopsy is indicated.

Metastases.—Skull base metastases are rare. Patients can be asymptomatic or experience cranial neuropathy or craniofacial pain. In this location, the metastasis of several primary cancers has been reported, including breast cancer, prostate cancer, lung cancer, renal cell carcinoma, thyroid cancer, melanoma, and hepatocarcinoma. CT (Fig 18) shows bone erosion or destruction, with a soft-tissue mass. MRI can allow detection of infiltration of the dura or cranial nerves. The medical history of a known primary tumor supports the diagnosis (23,24).

Renal cell carcinoma metastases. Axial CT image shows bone erosion of                         the clivus and left occipital condyle with a soft-tissue mass (arrows). The                         findings represent metastases of renal cell carcinoma.

Figure 18. Renal cell carcinoma metastases. Axial CT image shows bone erosion of the clivus and left occipital condyle with a soft-tissue mass (arrows). The findings represent metastases of renal cell carcinoma.

Clival Chordoma.—Chordomas are infiltrative tumors originating from extradural vestiges of the notochord and therefore have a central location. Bone destruction and bone remnants inside tumors can be seen with CT (Fig 19a). Contrast-enhanced T1-weighted MRI shows an invasive mass with low signal intensity. Chordomas show characteristic high signal intensity at T2-weighted MRI, which can help to differentiate them from SBOs. Low-signal-intensity septa at T2-weighted MRI are also observed (Fig 19b) (25).

Clival chordoma in a 40-year-old man. (a) Axial contrast-enhanced CT                         image shows destruction of the sphenoid bone in the sellar region and                         clivus, occupied by a soft-tissue mass (arrows). (b) Sagittal T2-weighted MR                         image shows a mass with high signal intensity and septa (green arrows) and                         pontine compression (orange arrows).

Figure 19a. Clival chordoma in a 40-year-old man. (a) Axial contrast-enhanced CT image shows destruction of the sphenoid bone in the sellar region and clivus, occupied by a soft-tissue mass (arrows). (b) Sagittal T2-weighted MR image shows a mass with high signal intensity and septa (green arrows) and pontine compression (orange arrows).

Clival chordoma in a 40-year-old man. (a) Axial contrast-enhanced CT                         image shows destruction of the sphenoid bone in the sellar region and                         clivus, occupied by a soft-tissue mass (arrows). (b) Sagittal T2-weighted MR                         image shows a mass with high signal intensity and septa (green arrows) and                         pontine compression (orange arrows).

Figure 19b. Clival chordoma in a 40-year-old man. (a) Axial contrast-enhanced CT image shows destruction of the sphenoid bone in the sellar region and clivus, occupied by a soft-tissue mass (arrows). (b) Sagittal T2-weighted MR image shows a mass with high signal intensity and septa (green arrows) and pontine compression (orange arrows).

Giant Pituitary Macroadenoma.—Pituitary adenomas that are larger than 10 mm are called macroadenomas; if their size exceeds 40 mm, they are known are giant macroadenomas. At T1- and T2-weighted MRI, the tumor is usually isointense compared with the gray matter, but it can also be heterogeneous. All giant macroadenomas are centered in the pituitary fossa. The tumors can exhibit aggressive behavior, with invasion of the dura, sphenoid bone, cavernous sinus, or surrounding structures (Fig 20). In these patients, the clinical context helps in diagnosis. These patients can have symptoms related to hormonal hypersecretion (26).

Giant pituitary macroadenoma in a 55-year-old man. Axial                         contrast-enhanced CT image shows bone destruction of the sellar region and a                         poorly enhancing soft-tissue mass (arrows) with cavernous sinus invasion                         that is surrounding both internal carotid arteries (red dots).

Figure 20. Giant pituitary macroadenoma in a 55-year-old man. Axial contrast-enhanced CT image shows bone destruction of the sellar region and a poorly enhancing soft-tissue mass (arrows) with cavernous sinus invasion that is surrounding both internal carotid arteries (red dots).

Chondrosarcoma.—Craniofacial chondrosarcomas account for 2% of all chondrosarcomas and have a predilection for the skull base. These tumors usually originate in the petrooccipital fissure and therefore have a lateral location and involve the occipital bone, clivus, and sphenoid bone. CT reveals a mass with chondroid matrix mineralization (ie, a “ring-and-arc” pattern) and aggressive growth features (ie, bone destruction with a soft-tissue mass). Nonmineralized areas typically show high water content at both CT and MRI (Fig 21), with elevated diffusivity and high ADCs in the diffusion sequences. Contrast-enhanced imaging shows heterogeneous mild to intense enhancement. The presence of peripheral and septal enhancement is a feature that could help distinguish these lesions from other more vascular skull base diseases (27,28).

Chondrosarcoma in a 50-year-old woman. Axial T2-weighted MR image                         shows a hyperintense mass (arrows) with thin septa and bone erosion of the                         clivus and left occipital condyle.

Figure 21. Chondrosarcoma in a 50-year-old woman. Axial T2-weighted MR image shows a hyperintense mass (arrows) with thin septa and bone erosion of the clivus and left occipital condyle.

Multiple Myeloma.—Multiple myeloma consists of a proliferation of plasma cells that can infiltrate various organs and is the most frequent primary bone lesion in elderly patients. The cancer affects the active bone marrow and, in adults, remains in the spine, skull, pelvis, and ribs. In the skull, the cancer typically manifests as multiple rounded lytic lesions, with well-defined nonsclerotic edges that affect the outer and inner tables (Fig 22). Plain skull radiography shows a salt-and-pepper pattern when the lesions are small and a “punched-out” pattern when they are larger. CT also shows an increase in soft tissue. At T1-weighted MRI, the lesions are hypointense, and they are hyperintense at T2-weighted MRI, with contrast enhancement. In rare cases, there can be one large lesion (ie, plasmacytoma), thus requiring special attention to differentiate it from SBO. The classic triad of lytic bone lesions, a monoclonal component in urine and/or serum, and medullary plasmacytosis helps to guide the diagnosis (29).

Multiple myeloma in a 69-year-old man. Axial nonenhanced CT image                         shows lytic lesions (arrows) in the body of the sphenoid bone, clivus, and                         occipital condyle.

Figure 22. Multiple myeloma in a 69-year-old man. Axial nonenhanced CT image shows lytic lesions (arrows) in the body of the sphenoid bone, clivus, and occipital condyle.

Lymphoma.—Primary skull base lymphoma is a rare manifestation of extranodal lymphoma. According to Marinelli et al (30), a clinical history of multiple cranial nerve palsies, B symptoms, and imaging findings that rule out other common diseases should lead to suspicion for lymphoma. Analysis of cerebrospinal fluid can also provide diagnostic and prognostic value. At CT, the bone can appear normal or with surrounding hyperostosis and bone erosion. MRI will show replacement of the bone marrow signal intensity, restricted diffusion, absence of flow voids, and heterogeneous contrast enhancement. Bulky masses usually are located in the medulla and are associated with minimal cortical destruction. In primary bone lymphomas, the radiographic appearance is highly variable and can include an almost normal-looking bone, a focal lytic lesion with geographic margins, a mixed sclerotic-lytic lesion, or a diffusely permeative process with cortical destruction and soft-tissue involvement (Fig 23). An important feature is the presence of a bone sequestrum in the lesion that might suggest a diagnosis of lymphoma (30,31).

Lymphoma in a 60-year-old woman. Axial contrast-enhanced CT image                         shows a lytic lesion in the dorsum sellae (orange arrow) and an enhancing                         soft-tissue mass with bilateral cavernous sinus invasion that surrounds the                         right internal carotid artery (red areas) with right anterior temporal fossa                         invasion (green arrows).

Figure 23. Lymphoma in a 60-year-old woman. Axial contrast-enhanced CT image shows a lytic lesion in the dorsum sellae (orange arrow) and an enhancing soft-tissue mass with bilateral cavernous sinus invasion that surrounds the right internal carotid artery (red areas) with right anterior temporal fossa invasion (green arrows).

Nasopharyngeal Angiofibroma.—Nasopharyngeal angiofibromas are benign highly vascularized neoplasms with locally aggressive behavior that almost exclusively affect adolescent boys. This fact is fundamental to differentiation of these tumors from SBOs. T1- and T2-weighted MR images show an intermediate-signal-intensity mass, with multiple flow voids that are characteristic of the presence of intratumoral vessels. CT is useful for detection of bone involvement. Intense contrast material enhancement with rapid washout in subsequent phases is observed with both techniques. Biopsy should be avoided because of its high risk of bleeding. Angiography can demonstrate the origin of the tumor’s vascularization and enable preoperative embolization of the tumor, thereby reducing intraoperative bleeding (32,33).

Nonneoplastic Processes

Fibrous Dysplasia.—In fibrous dysplasia, bone is replaced by fibrous tissue, producing bone deformity and reduced cranial foramina and fissures. Patients can experience neuropathy secondary to nerve compression, as in SBO. CT characteristically shows bone expansion, with ground-glass internal attenuation. There is typically no bone erosion or a soft-tissue mass as there is in SBO. At T2-weighted MRI, the lesions can contain hyperintense cystic formations and strong enhancement after gadolinium administration. The exclusive bone involvement with no soft-tissue component allows differentiation of fibrous dysplasia from SBO (34).

Paget Disease.—Paget disease is characterized by increased bone turnover with excessive and abnormal bone remodeling. The skull is one of the most frequent sites involved. The radiographic skull findings depend on the disease stage. Osteolysis occurs during the early stage, and plain radiography and CT show osteoporosis circumscripta (large oval or well-defined round lytic lesions in the frontal or occipital bones). The second stage is referred to as the mixed phase, with trabecular and cortical thickening and bone enlargement. Disease progression to the last stage (blastic phase) causes a cotton-wool appearance, with mixed lytic and sclerotic lesions (Fig 24). In the blastic phase, the sclerotic areas become predominant. Given this progression, MRI can reveal more fat in the marrow space of the pagetic bone than in the uninvolved bone at the beginning of the disease. Subsequently, the second observed pattern shows heterogeneous signal intensity of the marrow space, with decreased signal intensity at T1-weighted MRI and elevated signal intensity (ie, a speckled appearance) at T2-weighted MRI that is secondary to hypervascularity. In the final stage, the sclerotic bone shows low signal intensity at both T1- and T2-weighted MRI. Bone scintigraphy demonstrates increased radionuclide uptake in all phases (35,36).

Paget disease of bone in an 85-year-old man. Axial nonenhanced CT                         image shows the skull base with a cotton-wool appearance, which indicates                         mixed lytic and sclerotic lesions (arrows).

Figure 24. Paget disease of bone in an 85-year-old man. Axial nonenhanced CT image shows the skull base with a cotton-wool appearance, which indicates mixed lytic and sclerotic lesions (arrows).

Inflammatory Pseudotumor.—Inflammatory pseudotumor is a rare condition with idiopathic pathogenesis that is more common in the orbits or lungs than in the skull base. When the lesion occurs in the skull base, it can affect the cranial nerves, as in SBO. The main CT finding is a soft-tissue infiltrating mass with enhancement in the contrast-enhanced phase. T1- and T2-weighted MRI images show low signal intensity because of the tumor’s fibrotic nature and a homogeneous signal intensity increase after administration of gadolinium (Fig 25). The standard procedure for diagnosis is biopsy, which reveals a chronic inflammatory infiltrate with lymphoid elements, both T and B cells (3740).

Orbital pseudotumor in a 25-year-old man. Axial contrast-enhanced                         T1-weighted MR images show an enhancing mass (arrows) in the orbital medial                         wall and apex that extends through the inferior orbital fissure.

Figure 25a. Orbital pseudotumor in a 25-year-old man. Axial contrast-enhanced T1-weighted MR images show an enhancing mass (arrows) in the orbital medial wall and apex that extends through the inferior orbital fissure.

Orbital pseudotumor in a 25-year-old man. Axial contrast-enhanced                         T1-weighted MR images show an enhancing mass (arrows) in the orbital medial                         wall and apex that extends through the inferior orbital fissure.

Figure 25b. Orbital pseudotumor in a 25-year-old man. Axial contrast-enhanced T1-weighted MR images show an enhancing mass (arrows) in the orbital medial wall and apex that extends through the inferior orbital fissure.

Immunoglobulin G4related Disease.Immunoglobulin G4–related disease (IgG4-RD) is a multisystem disease with a predilection for the head and neck. The skull base manifestations of IgG4-RD can include idiopathic orbital inflammatory disease, orbital myositis, hypophysitis, hypertrophic pachymeningitis, dacryoadenitis, and vasculitis. Some characteristics overlap with those described in inflammatory pseudotumors. IgG4-RD can manifest as an isolated skull base mass. For diagnosis, the laboratory tests include determining the serum ratio of IgG4 to immunoglobulin G1. CT shows bone erosion surrounding the mass, while T1- and T2-weighted MRI sequences reveal an isointense to hypointense mass with diffusion restriction. PET can help to identify biopsy sites and occult organ involvement. Biopsy is necessary to confirm the diagnosis and shows lymphoplasmacytic infiltration; repeated biopsies are often performed because of the dense fibrotic tissue (41,42).

Granulomatous Diseases.—Granulomatous diseases are a varied group that includes sarcoidosis, granulomatosis with polyangiitis, Churg-Strauss syndrome, Behçet disease, and even infectious conditions such as tuberculosis and catscratch disease. These multisystemic diseases share the characteristic formation of granulomas, which can be located in the skull base. At CT, the granulomas can be observed as a mass with heterogeneous enhancement and bone erosion or destruction. T1-weighted MRI shows an isointense or hypointense invasive mass, and T2-weighted MRI shows heterogeneous high signal intensity, with moderate to strong heterogeneous enhancement. The patient’s medical history and biopsy of the lesion help to guide the diagnosis (43,44).

Treatment and Prognosis

Given the clinical suspicion for SBO and compatible radiologic imaging, early empirical therapy with broad-spectrum intravenous antibiotics is essential. Adequate control of risk factors (such as diabetes) is also important. Intravenous antibiotics should be administered for at least 6 weeks (3,7,8), with subsequent oral antibacterial or antifungal therapy for 12–48 weeks (1,2,7,8,11).

Surgical débridement might be necessary in specific cases, including those with extensive soft-tissue involvement, severe pain despite antibiotic treatment, complications (abscess formation), or bone sequestrum, as well as refractory cases. Other management approaches for complications, such as endovascular therapy for pseudoaneurysms and anticoagulant therapy for venous sinus thrombosis, should be individualized (4,7,11).

Combining hyperbaric oxygen therapy can improve the treatment, given that it increases the partial pressure of oxygen, reverses tissue hypoxia, improves phagocytosis, and promotes angiogenesis and osteoneogenesis (4,7,11). Treatment consists of 100% oxygen administered for 90 minutes at 2.5 atmospheres of pressure 5 days a week for 1 month (4).

The global survival rates for SBO are approximately 90% at 18 months and 57% at 3 years (7). In the diabetic population, the survival rates decrease by 21%–70% (11). Depending on the study (3,4,7,11), the mortality rate ranges from 9.5% to 46%. The rate of neurologic sequelae is 31%–48% (2,7).

In our study, one of the patients died (16%) of complications of the disease (massive epistaxis due to rupture of the internal carotid artery pseudoaneurysm). Three of the patients fully recovered, and the other two (33%) have persistent neurologic sequelae such as cranial nerve palsy and neurosensorial deafness.

Conclusion

SBO is an uncommon but life-threatening condition. The typical patient is an elderly man with diabetes mellitus and an otogenic infection, and the most frequent bacterial infections are caused by P aeruginosa and S aureus. Causative pathogens in fungal infections depend on the study, but many authors agree that the most frequent fungal pathogen is Aspergillus species. The diagnosis should be based on the combination of clinical findings, medical history, imaging, and microbiologic and histologic findings.

Various imaging techniques support the diagnosis. CT shows bone erosion with a soft-tissue mass, while MRI is useful for evaluating the anatomic location and extent and shows an enhancing mass with an infiltrating pattern, bone marrow involvement, and adjacent soft-tissue edema. Nuclear imaging can allow confirmation of bone involvement and is useful for follow-up. Regardless of which imaging modality is used, a biopsy is always required.

Lastly, the diagnosis of SBO is frequently delayed because of its nonspecific symptoms, long clinical course, and radiologic findings that usually mimic those of malignancy. Therefore, the diagnosis of SBO requires a global perspective of the patients who are at risk, recognition of the more typical radiologic features, and inclusion of this rare entity in the differential diagnosis for skull base lesions.

Presented as an education exhibit at the 2019 RSNA Annual Meeting.

For this journal-based SA-CME activity, the authors, editor, and reviewers have disclosed no relevant relationships.

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Article History

Received: Mar 23 2020
Revision requested: Apr 23 2020
Revision received: July 6 2020
Accepted: July 16 2020
Published online: Jan 7 2021
Published in print: Jan 2021