Entrapment neuropathy caused by a schwannoma of the posterior tibial nerve – A case report and literature review

Schwannomas are benign encapsulated tumors derived from Schwann cells. The display a peak incidence in the 3rd −5th decades and have no gender predilection. More common in the head and neck their occurrence on a peripheral nerve of an extremity is a relative rarity. With regards schwannomas of the posterior tibial nerve their hidden location behind the tibia makes early detection difficult. A normal straight leg raising test together with a positive Tinel sign may be the only clinical signs present to raise suspicion of the diagnosis. As such these lesions are commonly only diagnosed radiographically unless they reach an appreciable size making palpation possible. The treatment of choice is surgical excision with many studies reporting the microscope and intra-operative neurophysiological monitoring as mandatory surgical adjuncts to ensure a good outcome. We present an adult female patient who presented to our unit with a neuropathy that were initially misdiagnosed as a S1 radiculopathy. Unlike the classical presentation in other case reports our patient's schwannoma had reached such an appreciable size that part of her presentation was a soft tissue mass on the posterolateral aspect of her left ankle protruding between the flexor hallucis longus and the flexor digitorum longus muscles. Utilizing loupe magnification and intra-operative neurophysiological monitoring we were able to perform a gross total resection incurring no iatrogenic damage to the fascicles of the parent nerve. We advocate magnification and intra-operative neurophysiological monitoring as essential adjuncts and recommend these be routinely employed by peripheral nerve surgeons involved in the resection of these lesions.