B-Scan Ultrasonography of Abdominal Mass Lesions

a mode ultrasound has been described as a means of differentiating abdominal masses (1, 6). External B-scan ultrasonography has also been applied to the diagnosis of abdominal disease, particularly in respect to the liver, spleen, and pelvic organs (2–5, 7). Preliminary use of this modality in the evaluation of other abdominal masses and the potential clinical applications are described.

Method

Patients with abdominal masses evident clinically or radiographically were studied. They were examined by a contact rescanning technic in which a compound arc-sector movement was performed manually. A 2 mHz transducer with a diameter of 13 mm was used, with a pulse of two microseconds at a rate of 500 per second. The results were displayed on a retention oscilloscope and recorded with a Polaroid camera.

The largest diameter of the mass was found and related to an external landmark {e.g., umbilicus, costal margin, or iliac spine). Multiple scans were taken transversely from this point and extended both superiorly and inferiorly, depending on the size and shape of the mass. The gain settings used for each scan were recorded so that they might be reproduced and compared at a future date. They were also varied so that the echo-free fluid structures might be differentiated from the increased echoes obtained from solid tissue.

Discussion

Although depth resolution is excellent (approximately 1 mm for 2 mHz sound waves), the horizontal resolution is limited by the diameter of the transducer itself (13 mm). This is partially obviated by the sector movement during the scan, which detects some of the acoustical interfaces not perpendicular to the body surface. Nevertheless, abdominal lesions less than 4 to 5 cm in diameter would be difficult to detect reliably with this equipment. Another problem is the presence of gas within interposed loops of bowel, which effectively blocks the transmission of the sound waves and creates disturbing patterns by its reflections. A concurrent radiograph obtained with the patient in the same position may assist in interpretation.

Despite these difficulties, the graphic representation of an abdominal mass in cross section—which cannot be displayed by any other technic—does have potential clinical value. The regression and recurrence of a neoplasm after radiation, chemotherapy, or surgery may be documented by serial sonograms. In this manner not only can the course of an individual patient be followed, but also the effectiveness of a specific modality, such as a particular chemotherapeutic agent or radiotherapeutic regimen, may be evaluated in a more objective manner. This evaluation could be accomplished by calculating the approximate tumor volume from measurements obtained on transverse and longitudinal scans at predetermined times during and after therapy for a given type of neoplasm. The sonogram may also assist in the placement of treatment ports for radiotherapy.