Sciatic entrapment neuropathy associated with an anomalous piriformis muscle.

Piriformis syndrome is an often overlooked cause of sciatica that typically responds to intramuscular local anesthetic and steroid injection. In this report, our patient presented with sciatica that responded poorly to epidural steroid injection and only transiently to piriformis injection. Surgical exploration of the sciatic nerve revealed a fascial constricting band around the nerve as well as a piriformis muscle lying anterior to the nerve. This unusual anatomical relationship between the piriformis and the sciatic nerve has not been previously described in the literature. Subsequent sectioning of the anomalous muscle and the constricting band yielded complete resolution of our patient's symptoms.