Compression of the peroneal nerve by a neurofibroma originating from collaterals of the peroneal nerve: a case report

BACKGROUND Paralysis of the external popliteal sciatic nerve is a frequent pathological condition that occurs after trauma. However, etiologies other than trauma, such as tumors, are also possible. The sensory collaterals of the external popliteal sciatic nerve have a small territory of innervation at the knee, and tumors involving these nerves become symptomatic after compression of the motor nerves. We here describe the first reported case of this phenomenon. CASE PRESENTATION This case involved a lesion compressing the origin of the external popliteal sciatic nerve of a 13-year-old Moroccan boy diagnosed with a neurofibroma. He developed functional impairment of his left lower limb during a football game, and examination revealed a steppage gait. The initial diagnosis was stretching of the peroneal nerve. The definitive diagnosis of a neurofibroma was revealed by imaging and confirmed by surgery and pathology. Treatment involved total removal of the tumor; however, our patient's steppage gait persisted. CONCLUSIONS Our patient developed compression of the external popliteal sciatic nerve from a tumor growing on a collateral nerve. Early diagnosis is an absolute necessity in such cases. Trauma and tumors of sensory nerves can distort the diagnosis, as in this case. Ultrasound and magnetic resonance imaging can contribute to an accurate diagnosis in patients with neuropathy in the absence trauma or tomacula.