Entrapment neuropathy in the foot revealing schwannoma of the superficial peroneal nerve: outcome of conservative surgical treatment

We report the case of a 61-year old patient with no particular previous history who complained of pain with paraesthesias at the level of the anterolateral compartment of the left leg irradiating to the dorsal side of the ankle and the foot which lasted over six months. These pains were made worse by effort. Clinical examination showed partial sensitivity deficit and positive Tinel's sign in the territory of the superficial peroneal nerve (A). Electromyography (EMG) confirmed peroneal nerve involvement with decreased amplitude of sensory potentials. X-ray ruled out the presence of an underlying osteo articular cause (B). Ultrasound objectified well-defined homogeneous tissue formation (C) while MRI showed fusiform mass centered on the nerve with contrast-enhanced T1-weighted hyposignal and T2-weighted hypersignal (D). Conservative surgical resection with sparing of nerve fascicles (E,F) and anatomopathological examination confirmed the diagnosis of benign schwannoma (G). At 1-month follow-up, symptoms had disappeared with sensitivity conservation in the territory of this nerve. The diagnosis of schwannoma is difficult due to the absence of swelling and because schwannoma may mimic entrapment neuropathy, as in the case of our patient. Schwannomas are resectable peripheral nerve tumors. Their prognosis is excellent after adapted surgical treatment with sparing of nerve fascicles.