Recurrent ganglion cyst of the peroneal nerve: radiological and operative observations Case report

ERONEAL nerve neuropathy can be induced by several conditions, such as mononeuritis, external compressive neuropathy, and tumors. Intraneural synovial cyst of the peroneal nerve, another possible cause, has been described in single case reports or in small series of two or three cases. In the current report, we recount our experience with an additional case of peroneal nerve neuropathy. The case is of particular interest with regard to its etiology, and to the value of using ultrasonography (US) and, particularly, magnetic resonance (MR) imaging for specific diagnosis and to determine the causes of recurrence. Case Report This 34-year-old man, an amateur drummer, presented with a 4-week history of right foot drop. The condition had been preceded by some back discomfort, followed by pain in the lateral aspect of the right leg. Examination. Physical examination showed moderate wasting of the tibialis anterior and hallux extensor muscles with complete paralysis of the right foot dorsiflexion although eversion was preserved. Deep tendon reflexes were normal on both lower limbs. Sensory testing revealed hypesthesia over a small area at the dorsal aspect of the right foot. No mass could be located by palpation in the popliteal space, over the head of the fibula, or along the lateral leg, and no paresthesia was elicited on palpation and percussion. Examination of the patient's back and the straight leg raising test yielded negative results. Because of the patient's complaints of back discomfort, lumbar plain x-ray study, myelography, and computerized tomography were first performed; these ruled out a radicular lesion. On the right leg, electromyography revealed many fibrillations in the tibialis anterior muscle and none in the peroneus lateralis longus muscle; conduction velocity was markedly diminished at the proximal deep peroneal nerve. Plain x-ray films of the right knee and leg were normal. On US a fusiform, markedly hypechogenic mass, measuring 3 cm ϫ 10 cm, was seen in the lateral muscle compartment between the fibula and the tibia (Fig. 1). Computerized tomography confirmed that the mass was well defined and indicated a course within the deep peroneal nerve. Magnetic resonance imaging showed the mass to