Compressive Neuropathy of the Common Peroneal Nerve due to Popliteal Cyst: A Case Report

Abstract

Popliteal cysts occur commonly, but those causing compressive neuropathy are unusual. We report a case with compressive neuropathy of the common peroneal nerve by a popliteal cyst. A 45-year old woman with a two month history of an asymptomatic popliteal mass in her left lateral knee visited our outpatient clinic due to persistent symptoms. Physical examination revealed an approximately 4 cm soft elastic mass on the postlateral aspect of her left knee and she complained lateral cruris numbness during full flexion of her knee. Radiographs were normal, but magnetic resonance imaging showed a cystic mass measuring 5 × 3 × 3 cm in the popliteal fossa. That cyst was located between the popliteal tendon and the lateral head of the gastrocnemius through to the fibular collateral ligament and the common peroneal nerve went along the interval. Arthrography showed no communication between the cyst and joint. We performed surgical excision of the cyst directly, and the histologic diagnosis was a politeal cyst. Postoperatively she had no numbness during flexion of her knee.