US of Soft-Tissue Foreign Bodies and Associated Complications with Surgical Correlation
Abstract
Ultrasonography (US) allows detection of a variety of soft-tissue foreign bodies, including wood splinters, glass, metal, and plastic, along with evaluation of their associated soft-tissue complications. Cases were obtained from the authors’ clinical experience over the past 1.5 years. Surgical correlation allowed confirmation of the presence of a foreign body and associated soft-tissue complications in all cases. All of the foreign bodies were echogenic when imaged with US. A surrounding hypoechoic rim and posterior acoustic shadowing or reverberation aided detection in several cases. Associated soft-tissue complications included a complete laceration of the posterior tibial tendon and septic flexor digitorum tenosynovitis. US allows accurate and efficient detection of radiolucent soft-tissue foreign bodies and aids assessment of their associated complications. For radiopaque foreign bodies, US can provide more precise localization and improved assessment of the surrounding soft tissues. US has emerged as the study of choice for detection and localization of radiolucent soft-tissue foreign bodies and can aid assessment of their associated complications.
Introduction
Penetrating injuries and suspected retained foreign bodies are a common reason for emergency department visits. Anderson et al (,1) reported that 38% of retained foreign bodies in the soft tissues were overlooked at initial examination. The most common retained foreign bodies are wood, glass, or metal slivers (,1). Only 15% or less of wooden foreign bodies are detected with radiography (,1). Detection is important because retained foreign bodies may lead to serious infectious and inflammatory complications (,1–,3). Not infrequently, such cases also result in malpractice lawsuits (,3).
Multiple cadaveric studies have examined the effectiveness of ultrasonography (US) in detection of superficial, nonradiopaque foreign bodies. In a multioperator, blinded study performed with 7.5- and 10-MHz transducers, Jacobson et al (,3) identified 2.5-mm-long wooden foreign bodies with a sensitivity of 87% and specificity of 97% and 5-mm-long wooden foreign bodies with a sensitivity of 93% and specificity of 97%. Blyme et al (,4) achieved a similar sensitivity of 89% and specificity of 93% for detection of glass, plastic, and wooden foreign bodies implanted in cadaveric thighs. In an in vitro study of cadaveric hands, US allowed localization of glass, metal, and wooden foreign bodies with a sensitivity of 94% and specificity of 99% (,2). An in vivo study of 50 patients with suspected nonradiopaque foreign bodies demonstrated a sensitivity of 95% and specificity of 89% for US detection (,5). US has been shown to accurately demonstrate the size, shape, and location of soft-tissue foreign bodies (,2,,6).
This article illustrates the clinical usefulness of US in evaluating a variety of soft-tissue foreign bodies and their associated complications. Specific topics discussed are technique, US findings, and the role of US. The cases presented are from our clinical experience over the past 1.5 years.
Technique
A high-frequency (7.5-MHz or higher) linear-array transducer is optimal for US evaluation of soft-tissue foreign bodies. Owing to the improved near-field resolution of high-frequency transducers, a standoff pad is not routinely used at our institution. The area of interest is scanned in both the longitudinal and transverse orientations, with attention to detection of a foreign body and its associated posterior acoustic shadowing or reverberation. US allows determination of the precise location of the foreign body, as well as its size, shape, and orientation, and aids skin marking for removal. The surrounding soft tissues are also examined for fluid collections, tendon disorders, and injury to neurovascular structures.
US Findings
US allows detection of a variety of soft-tissue foreign bodies, including wood splinters (,,,Figs 1,,,,,,,,,,–,,,,5), glass (,,,Fig 6), metal (,Fig 7), and plastic (,Fig 8). Surgical correlation allowed confirmation of the presence of a foreign body and associated soft-tissue complications in all cases. All foreign bodies were surgically removed without complications following US localization. We did not attempt to determine the accuracy of US for detection of foreign bodies, as has previously been done (,2–,5,,7). It is unknown if false-positive or false-negative US results occurred during the period of our clinical experience.
Echogenicity of the Foreign Body
The degree of echogenicity of a given foreign body is proportional to the differences in acoustic impedance at the interface of the foreign body and surrounding tissue. We found all foreign bodies to be echogenic, consistent with results of prior studies (,2–,7). Metal and glass foreign bodies are visible on radiographs. However, the exact location of a radiopaque foreign body, its relationship to surrounding structures, and the degree of associated soft-tissue injuries are not always apparent at radiography and can be further defined with US (,,,,,Figs 4, ,,,6).
Posterior Shadowing and Reverberation
The artifact occurring deep to a foreign body depends primarily on its surface attributes rather than its composition. Smooth and flat surfaces produce dirty shadowing or reverberation artifact (,Fig 8), whereas irregular surfaces and those with a small radius of curvature produce clean shadowing (,8). Metal and glass often demonstrate reverberation due to their flat surfaces (,2,,8). However, a flat surface not imaged perpendicular to the ultrasound beam may not produce reverberation, as was noted with a glass foreign body (,,,Fig 6) and a hypodermic needle (,Fig 7). Some foreign bodies produce both clean and dirty shadowing (,,,Fig 1) (,2,,8).
Surrounding Hypoechoic Rim
A surrounding hypoechoic rim aided detection in several cases. If a foreign body is present in the soft tissues longer than about 24 hours, the ensuing inflammatory reaction can create a hypoechoic rim around the echogenic foreign body (,Fig 2). This hypoechoic rim improves the sensitivity and specificity of the US examination (,3).
Associated Soft-Tissue Complications
US allows examination of the surrounding muscles, tendons, ligaments, and neurovascular structures and assessment of associated injuries. Soft-tissue infection is by far the most common complication of a penetrating foreign body, with nerve injury a distant second (,1). US allowed identification of foreign bodies in the soft tissues superficial to intact plantar fascia and plantar tendons (,Figs 2, ,8). US allowed localization of a foreign body superficial to the flexor digitorum profundus tendon, and removal was easily accomplished in the emergency department (,,,,Fig 3). In another patient, US allowed localization of a foreign body superficial to the flexor digitorum profundus tendon but also demonstrated flexor tenosynovitis, which necessitated surgical incision and drainage (,,,,,Fig 4). US allowed correct identification of a complete rupture of the posterior tibial tendon secondary to laceration by a glass foreign body (,,,Fig 6).
Role of US
For detection of superficial, nonradiopaque foreign bodies, US has been shown to be more effective than computed tomography (CT) (,7). CT also has a higher cost, involves ionizing radiation, may have limited availability, and can involve anesthesia in pediatric cases (,6). Magnetic resonance (MR) imaging also has a higher cost and more limited availability than US; in addition, MR imaging often does not allow differentiation of foreign bodies that have low signal intensity from other structures that can have low signal intensity, such as scar tissue, tendons, and calcifications (,3).
Limitations of US evaluation for soft-tissue foreign bodies include operator dependence. Familiarity with the US appearances of soft-tissue foreign bodies and a systematic evaluation of the region of interest in both the longitudinal and transverse orientations are needed for accurate assessment. A high-frequency linear transducer (7.5 MHz or higher) is needed to optimize near-field spatial resolution. The average examination time for US evaluation of soft-tissue foreign bodies has been reported to be approximately 10 minutes (,6).
In addition, US has been proved effective only for superficial foreign bodies. Foreign bodies and their accompanying shadowing or reverberation may not be well visualized if they are located adjacent to bone or deep to subcutaneous gas (,2,,7). In such cases, US may be less accurate. False-positive findings can potentially result from calcification, scar tissue, fresh hematoma, or air trapped in the soft tissues (,2,,3,,5). Surgical exploration can introduce air into the soft tissues. In our experience, soft-tissue air is rarely present in an amount that causes difficulty if imaging is done prior to surgical exploration. Calcifications typically appear as rounded echogenic foci with strong posterior shadowing and are radiopaque. Correlation with radiographs is always recommended. Scar tissue and hematomas are solid mass lesions and usually would not be confused with a linear echogenic foreign body. Hematomas can have variable echogenicity depending on the presence of fluid components. In our clinical experience, these potential sources of confusion rarely cause false-positive results.
Conclusions
US is an inexpensive, portable, and readily available imaging modality for superficial soft tissues without the risk of ionizing radiation. US has emerged as the study of choice for detection of radiolucent foreign bodies (,2–,7). For radiopaque foreign bodies, US can provide more precise localization. For all foreign bodies, US can aid assessment of the surrounding soft tissues and demonstrate associated soft-tissue complications.
Figure 1a. Wood splinter in the volar surface of the hand in a 37-year-old man. (a) Radiograph (carpal tunnel view) shows no radiopaque foreign body in the volar soft tissues. A lateral radiograph also showed no radiopaque foreign body. The marker anterior to the volar soft tissues (a ballpoint pen) denotes the entry site of the suspected foreign body. (b) Longitudinal sonogram shows an echogenic foreign body (large arrows) 6 mm deep to the skin surface. Slight posterior acoustic shadowing (small arrows) and reverberation (arrowheads) are noted. US was used for preoperative localization and skin marking. A wood splinter was surgically removed from the thenar eminence without complications. On all US images, the skin surface is at the top of the image.
Figure 1b. Wood splinter in the volar surface of the hand in a 37-year-old man. (a) Radiograph (carpal tunnel view) shows no radiopaque foreign body in the volar soft tissues. A lateral radiograph also showed no radiopaque foreign body. The marker anterior to the volar soft tissues (a ballpoint pen) denotes the entry site of the suspected foreign body. (b) Longitudinal sonogram shows an echogenic foreign body (large arrows) 6 mm deep to the skin surface. Slight posterior acoustic shadowing (small arrows) and reverberation (arrowheads) are noted. US was used for preoperative localization and skin marking. A wood splinter was surgically removed from the thenar eminence without complications. On all US images, the skin surface is at the top of the image.
Figure 2. Wood splinter in a 6-year-old boy with continued left foot pain 1 month after stepping on a wood splinter. Longitudinal sonogram shows an echogenic foreign body (between cursors) with a surrounding hypoechoic rim (arrowheads) in the plantar soft tissues. A radiopaque foreign body was not seen on radiographs. A wood splinter was surgically removed without complications.
Figure 3a. Oak splinter in the distal finger in a 55-year-old man. (a) Lateral radiograph of the distal left ring finger shows a faint area of increased opacity in the volar soft tissues (arrow), which is suspicious for a foreign body. (b) Sonogram obtained along the long axis of the finger shows a foreign body (large arrowhead) superficial to the insertion of the flexor digitorum profundus tendon (arrows) on the echogenic cortex of the distal tuft (small arrowheads). Proximal is on the left side of the image; distal is on the right side. (c) Transverse sonogram shows a 15-mm-long hyperechoic structure (between cursors) located 5 mm deep to the volar skin surface and superficial to the cortex of the distal tuft (arrowhead). A wood splinter was removed in the emergency department without complication.
Figure 3b. Oak splinter in the distal finger in a 55-year-old man. (a) Lateral radiograph of the distal left ring finger shows a faint area of increased opacity in the volar soft tissues (arrow), which is suspicious for a foreign body. (b) Sonogram obtained along the long axis of the finger shows a foreign body (large arrowhead) superficial to the insertion of the flexor digitorum profundus tendon (arrows) on the echogenic cortex of the distal tuft (small arrowheads). Proximal is on the left side of the image; distal is on the right side. (c) Transverse sonogram shows a 15-mm-long hyperechoic structure (between cursors) located 5 mm deep to the volar skin surface and superficial to the cortex of the distal tuft (arrowhead). A wood splinter was removed in the emergency department without complication.
Figure 3c. Oak splinter in the distal finger in a 55-year-old man. (a) Lateral radiograph of the distal left ring finger shows a faint area of increased opacity in the volar soft tissues (arrow), which is suspicious for a foreign body. (b) Sonogram obtained along the long axis of the finger shows a foreign body (large arrowhead) superficial to the insertion of the flexor digitorum profundus tendon (arrows) on the echogenic cortex of the distal tuft (small arrowheads). Proximal is on the left side of the image; distal is on the right side. (c) Transverse sonogram shows a 15-mm-long hyperechoic structure (between cursors) located 5 mm deep to the volar skin surface and superficial to the cortex of the distal tuft (arrowhead). A wood splinter was removed in the emergency department without complication.
Figure 4a. Wood splinter in a 44-year-old man with a 10-day history of a swollen, red finger. (a) Sonogram obtained along the long axis of the finger shows a foreign body (large arrowhead) superficial to the insertion of the flexor digitorum profundus tendon (arrows). In addition, hypoechoic fluid (small arrowheads) is noted surrounding the tendon. Proximal is on the left side of the image; distal is on the right side. (b) Sonogram obtained along the long axis of the finger at the level of the proximal interphalangeal joint (arrowhead) shows the flexor tendon with surrounding hypoechoic fluid (arrows). (c) Sonogram obtained transverse and slightly oblique to the long axis of the finger shows the foreign body (between cursors), which is 10 mm long and surrounded by hypoechoic fluid (arrows). (d) Photograph of the surgical specimen shows a 10-mm-long wood splinter. The flexor tendon sheath was incised and drained. Biopsy of synovial tissue surrounding the flexor tendon demonstrated acid-fast bacilli.
Figure 4b. Wood splinter in a 44-year-old man with a 10-day history of a swollen, red finger. (a) Sonogram obtained along the long axis of the finger shows a foreign body (large arrowhead) superficial to the insertion of the flexor digitorum profundus tendon (arrows). In addition, hypoechoic fluid (small arrowheads) is noted surrounding the tendon. Proximal is on the left side of the image; distal is on the right side. (b) Sonogram obtained along the long axis of the finger at the level of the proximal interphalangeal joint (arrowhead) shows the flexor tendon with surrounding hypoechoic fluid (arrows). (c) Sonogram obtained transverse and slightly oblique to the long axis of the finger shows the foreign body (between cursors), which is 10 mm long and surrounded by hypoechoic fluid (arrows). (d) Photograph of the surgical specimen shows a 10-mm-long wood splinter. The flexor tendon sheath was incised and drained. Biopsy of synovial tissue surrounding the flexor tendon demonstrated acid-fast bacilli.
Figure 4c. Wood splinter in a 44-year-old man with a 10-day history of a swollen, red finger. (a) Sonogram obtained along the long axis of the finger shows a foreign body (large arrowhead) superficial to the insertion of the flexor digitorum profundus tendon (arrows). In addition, hypoechoic fluid (small arrowheads) is noted surrounding the tendon. Proximal is on the left side of the image; distal is on the right side. (b) Sonogram obtained along the long axis of the finger at the level of the proximal interphalangeal joint (arrowhead) shows the flexor tendon with surrounding hypoechoic fluid (arrows). (c) Sonogram obtained transverse and slightly oblique to the long axis of the finger shows the foreign body (between cursors), which is 10 mm long and surrounded by hypoechoic fluid (arrows). (d) Photograph of the surgical specimen shows a 10-mm-long wood splinter. The flexor tendon sheath was incised and drained. Biopsy of synovial tissue surrounding the flexor tendon demonstrated acid-fast bacilli.
Figure 4d. Wood splinter in a 44-year-old man with a 10-day history of a swollen, red finger. (a) Sonogram obtained along the long axis of the finger shows a foreign body (large arrowhead) superficial to the insertion of the flexor digitorum profundus tendon (arrows). In addition, hypoechoic fluid (small arrowheads) is noted surrounding the tendon. Proximal is on the left side of the image; distal is on the right side. (b) Sonogram obtained along the long axis of the finger at the level of the proximal interphalangeal joint (arrowhead) shows the flexor tendon with surrounding hypoechoic fluid (arrows). (c) Sonogram obtained transverse and slightly oblique to the long axis of the finger shows the foreign body (between cursors), which is 10 mm long and surrounded by hypoechoic fluid (arrows). (d) Photograph of the surgical specimen shows a 10-mm-long wood splinter. The flexor tendon sheath was incised and drained. Biopsy of synovial tissue surrounding the flexor tendon demonstrated acid-fast bacilli.
Figure 5a. Wood splinter in a 44-year-old man who fell from a tree. (a, b) Longitudinal (a) and transverse (b) sonograms of the prepatellar soft tissues show a linear foreign body (large arrow) with clean shadowing (small arrows) on the transverse image (b) and slight shadowing (large arrowheads) on the longitudinal image (a). The foreign body appears hollow due to strong peripheral echoes and lack of central echoes. It is surrounded by a small hypoechoic region (small arrowheads), likely fluid, on the transverse image (b). Radiographs were not available. (c) Photograph of the surgical specimen shows a 16-mm-long wood splinter.
Figure 5b. Wood splinter in a 44-year-old man who fell from a tree. (a, b) Longitudinal (a) and transverse (b) sonograms of the prepatellar soft tissues show a linear foreign body (large arrow) with clean shadowing (small arrows) on the transverse image (b) and slight shadowing (large arrowheads) on the longitudinal image (a). The foreign body appears hollow due to strong peripheral echoes and lack of central echoes. It is surrounded by a small hypoechoic region (small arrowheads), likely fluid, on the transverse image (b). Radiographs were not available. (c) Photograph of the surgical specimen shows a 16-mm-long wood splinter.
Figure 5c. Wood splinter in a 44-year-old man who fell from a tree. (a, b) Longitudinal (a) and transverse (b) sonograms of the prepatellar soft tissues show a linear foreign body (large arrow) with clean shadowing (small arrows) on the transverse image (b) and slight shadowing (large arrowheads) on the longitudinal image (a). The foreign body appears hollow due to strong peripheral echoes and lack of central echoes. It is surrounded by a small hypoechoic region (small arrowheads), likely fluid, on the transverse image (b). Radiographs were not available. (c) Photograph of the surgical specimen shows a 16-mm-long wood splinter.
Figure 6a. Glass splinter in a 56-year-old man with foot pain after stepping on glass. (a) Transverse sonogram obtained at the medial malleolus (large arrowheads) shows a 5-mm-long triangular foreign body (between cursors). It is surrounded by a slightly hypoechoic region (small arrowheads) and demonstrates posterior shadowing (arrows). A small area of increased opacity suggestive of a foreign body was noted inferior to the medial malleolus on anteroposterior radiographs but was not visible on lateral radiographs due to superimposed bone. (b) Longitudinal sonogram obtained just proximal to the medial malleolus shows complete laceration of the posterior tibial tendon (arrow) by the foreign body, with retraction of the proximal tendon stump. The echogenic tibial cortex is noted (arrowheads). Proximal is on the left side of the image; distal is on the right side. A triangular glass splinter was removed following US localization, and the tendon was surgically repaired.
Figure 6b. Glass splinter in a 56-year-old man with foot pain after stepping on glass. (a) Transverse sonogram obtained at the medial malleolus (large arrowheads) shows a 5-mm-long triangular foreign body (between cursors). It is surrounded by a slightly hypoechoic region (small arrowheads) and demonstrates posterior shadowing (arrows). A small area of increased opacity suggestive of a foreign body was noted inferior to the medial malleolus on anteroposterior radiographs but was not visible on lateral radiographs due to superimposed bone. (b) Longitudinal sonogram obtained just proximal to the medial malleolus shows complete laceration of the posterior tibial tendon (arrow) by the foreign body, with retraction of the proximal tendon stump. The echogenic tibial cortex is noted (arrowheads). Proximal is on the left side of the image; distal is on the right side. A triangular glass splinter was removed following US localization, and the tendon was surgically repaired.
Figure 7. Metal foreign body in a 64-year-old woman with diabetes mellitus who stepped on a hypodermic needle. Sonogram obtained along the long axis of the foot shows an 8-mm-long echogenic structure (between cursors). No reverberation is identified. A metallic needle fragment was visible on radiographs and was removed at surgery without complications.
Figure 8. Plastic foreign body in a 16-year-old boy with a plantar mass. Sonogram obtained along the long axis of the foot shows a linear echogenic structure (between cursors) in the plantar soft tissues, superficial to the plantar tendons and fascia. Posterior acoustic shadowing (arrowheads) is noted. Radiographs demonstrated no radiopaque foreign body. A plastic foreign body was removed at surgery without complications.
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