Intraneural ganglion cyst on the external popliteal nerve.

There are many causes for the paralysis of the external sciatic popliteal nerve , such as the intraneural ganglion cyst. In this case, we evaluate a 52-year-old woman with no relevant personal record, who was admitted with paresis of the right foot of 4 months of evolution associated with alterations in the sensitivity that rose up to the posterolateral region of the leg. The diagnosis was based on MR and cyst decompression and disconnection of the articular branch. Given the low incidence of these lesions, their origin is still subject to controversy. The most widely accepted theory is the unifying articular theory described by Spinner in the year 2003. Intraneural ganglion cysts must be included in the differential diagnosis of progressive paralysis of the sciatic nerve, lesions of the nerve root at L5 and nerve sheath tumours that start at the lateral compartment of the knee. The treatment of a fibular intraneural ganglion cyst must be surgical and the operation must be performed as soon as possible.