Compression of the peroneal nerve by a cyst in a seven-year-old child.

Compressions of the peroneal nerve are rare since only some sixty such cases have been described since 1921. The authors report a new observation of compression extrinsic to the peroneal nerve by a synovial cyst, the source of which was the upper fibulo-tibial joint, in a child of seven years. As far as we know, this is the youngest age found in the relevant literature. Because of a swiftly appearing painful swelling, along with complete paralysis of the peroneal nerve, an electromyogram and a nuclear magnetic resonance were performed, with a view to confirming the diagnosis and to clarifying the topography of the cyst. The removal of the latter led to the child being cured with complete recovery of the peroneal nerve within three months.