Common peroneal nerve schwannoma: an unusual differential for a symptomatic knee lump

Abstract

A 60-year-old woman with no medical history presented to the emergency department with worsening knee pain after a short-haul flight. She had a 2 year history of intermittent left knee pain, made worse by crouching and a lump at the back of her leg, which was gradually increasing in size. On examination, she was found to have a 34 cm lump behind the posterolateral aspect of the left knee. The lump was located in the subcutaneous plane, firm in consistency, deep to the fascia and was mobile in the horizontal plane. It did not transilluminate and was not fluctuant. No other lumps were palpable and there were no distal neurological signs. Her investigations including blood results, D-dimer and venous ultrasound were unremarkable. An MRI (figure