Successful surgical treatment of an intraneural ganglion of the common peroneal nerve.

Intraneural ganglion cysts of peripheral nerves occurring within the epineural sheath are rare, and their mechanism of formation and treatment options are debated. We present a case of a 41-year-old man who presented with a complaint of lateral-sided left knee pain with numbness on the lateral side of the foot who was diagnosed with an intraneural ganglion of the common peroneal nerve (CPN). He was treated initially with common peroneal epineural decompression only to have symptoms recur 6 weeks postoperatively. The patient was subsequently treated utilizing the suggestions of the "unified articular theory," which proposes a small recurrent articular branch of the CPN as the source of cyst fluid. This branch was surgically detached, leading to complete alleviation of his symptoms. When the patient was reevaluated 2 years postoperatively, his preoperative symptoms had resolved, and a follow-up magnetic resonance image showed resolution of the enlargement of the CPN.