Review Question - QID 219540

The patient has a symptomatic neurilemmoma (Schwannoma) of the superficial peroneal nerve that should be definitively managed with marginal excision.

Schwannomas are benign, encapsulated nerve sheath tumors composed of Schwann cells that occur on the surface of peripheral nerves. They most commonly present in the third to sixth decades of life with paresthesias in the distribution of the affected peripheral nerve. MRI typically shows a low intensity (dark), well-circumscribed lesion on T1 contiguous with the affected nerve that is high-intensity (bright) on T2 imaging and enhances diffusely with gadolinium contrast. If the diagnosis is in question, a biopsy can be performed and will show well-encapsulated nerve sheath tissue with histology showing verocay bodies and +S100 immunostaining. Asymptomatic lesions can be observed, but definitive treatment of symptomatic lesions involves marginal resection given that the lesions are benign in nature.

Albert et al. provide a review of varying clinical presentations and imaging findings of peripheral nerve Schwannomas. The authors note that the incidence of a Schwannoma occurring in the foot and ankle is rare, with prevalence rate of 1% to 10%. They present 3 cases of benign Schwannoma in the lower extremity, all of whom presented with varying clinical symptoms, including pain, paresthesia, weakness, and a palpable mass. They concluded that Schwannoma lesions are especially uncommon in the foot and ankle, and because they are generally asymptomatic, a delay in making the diagnosis often occurs; however, proper clinical and imaging interrogation can aid in the diagnosis.

Godkin et al. provide a case report of a large Schwannoma of the sciatic nerve. The authors note that a Schwannoma is the most common benign peripheral nerve sheath tumor composed of Schwann cells, representing 8% of all soft tissue tumors, with sciatic nerve involvement being <1%. They conclude that treatment of this epineurium encapsulated tumor is by delicate excision, en masse with nerve preservation followed by histopathology for definitive diagnosis.

Figures A and B represent coronal STIR and axial T2 fat-saturated MRI sequences demonstrating an encapsulated, high-intensity mass contiguous with the superficial peroneal nerve, most consistent with a Schwannoma.

Incorrect Answers:
Answer 1: There is no vascular pathology shown on the MRI.
Answer 3: Observation can be employed for asymptomatic patients, but this patient has unrelenting paresthesias.
Answer 4: The MRIs demonstrate a neurilemmoma, not a vascular lesion.
Answer 5: Schwannomas are benign masses and require marginal resection at most, with wide resection being excessively morbid in terms of neural sacrifice.