Intraneural cyst of the peroneal nerve

A 15-year-old girl was referred to us because of foot drop. The motor deficit was characterized by a peculiar fluctuating course related to sporting activity: improvement of symptoms during no-sport periods and worsening during sport training. Neurophysiological examination revealed marked global impairment of muscles innervated by the peroneal nerve. Ultrasound and MRI showed a mass in close proximity to the neck of the fibula extending in a tubular fashion. At operation an intraneural lesion was found and was totally removed. Histology revealed that it was an intraneural cyst. A hypothesis on the pathogenesis was drawn up. One year after the operation a clinical and neurophysiological follow-up was performed.