Sonography of peripheral nerves of the extremities.

High-resolution sonography can visualize segments of the major nerve trunks in the extremities, with nerves displaying a characteristic hyperechoic appearance. Sonography can also establish the diagnosis of nerve sheath tumors when the normal nerve is visualized. Other abnormalities that can be demonstrated by sonography include traumatic and Morton's neuromas and inflammatory changes. High-frequency probes up to 20.0 MHz are used. Both longitudinal and tranverse scans must be performed, strictly parallel and perpendicular to the nerve axis. In the upper extremities US demonstrates better than CT and MRI the radial and ulnar nerves in the elbow, the median nerve in the forearm and the carpal tunnel; in the lower extremities the sciatic, the tibial, the popliteal nerves are visualized, while both the deep and the superficial nerves are poorly demonstrated. Our experience leads us to the conclusion that the examination of nerves in the extremities is a promising new application of high resolution US. Indeed, the method can play a significant role in the diagnosis of pathologic conditions of nerves, particularly nerve sheath tumors, at a lower cost than MRI. However, the latter will remain the diagnostic procedure in areas of complex anatomy.