Compression neuropathy of common peroneal nerve caused by an extraneural ganglion: a report of two cases.

Peroneal nerve entrapment is most common in the popliteal fossa, but is rarely caused by a ganglion. Although ganglionic cysts are very common lesions, they seldom cause serious complications. Ganglionic cysts developing in the sheath of a peripheral nerve or joint capsule may cause compression neuropathy. We report on two cases of compression neuropathy of the common peroneal nerve caused by an extraneural ganglion and its evaluation with magnetic resonance imaging (MRI) and ultrasonography. The differential diagnosis should involve L5 root pathology, a posttraumatic intraneural hemorrhage, a nerve compression near the tendinous arch located at the fibular insertion of the peroneal longus muscle, and a nerve-sheath tumor. The combination of MRI and ultrasonography is useful for the accurate diagnosis of this condition, and it should be treated by microsurgical exploration as soon as possible.