Common Peroneal Nerve Schwannoma Presenting as a Popliteal Fossa Mass: A Case Report.

Schwannomas are benign peripheral nerve sheath tumors originating from Schwann cells and represent the most common benign tumors of peripheral nerves. Involvement of the common peroneal nerve is uncommon and may clinically mimic cystic, vascular, or other soft-tissue lesions of the popliteal fossa, leading to delayed diagnosis. We report the case of a 32-year-old woman who presented with a painless swelling in the left popliteal fossa, followed by progressive paresthesia extending to the dorsum of the foot and great toe. Ultrasound demonstrated a well-defined hypoechoic lesion adjacent to the popliteal vein, while magnetic resonance imaging (MRI) revealed a well-circumscribed spindle-shaped mass arising from the common peroneal nerve, with imaging characteristics suggestive of a benign peripheral nerve sheath tumor. In April 2024, the patient underwent complete surgical excision under general anesthesia at the Second Department of Orthopedics, KAT General Hospital of Attica. Histopathological examination confirmed the diagnosis of schwannoma. The postoperative course was uneventful, with gradual resolution of sensory symptoms and complete recovery within three months. Although uncommon and frequently misdiagnosed, common peroneal nerve schwannomas should be considered in the differential diagnosis of persistent popliteal fossa masses or unexplained neuropathic symptoms of the lower limb. MRI plays a pivotal role in diagnosis and surgical planning, while careful, complete excision is associated with excellent neurological and functional outcomes.