Piriformis syndrome--a rare cause of extraspinal sciatica.

Piriformis syndrome is a rare entity resulting in severe unilateral isolated buttock pain shooting in nature, non discogenic in origin. MR imaging of pelvis plays an important role in such patients to see the normal anatomy of piriformis muscle and its relationship with sciatic nerve. A 35-year-old woman presented with one year history of radiating leg pain with normal MR lumbosacral spine. MRI pelvis showed an abnormal orientation of left sciatic nerve through cleaved fibers of the piriformis muscle. The patient's symptoms were relieved by surgical decompression. The purpose of this case report is to show the role and importance of MR imaging for tracing sciatic nerve and its relationship to the Piriformis muscle. MR imaging of pelvis for sciatic nerve plays an important role in symptomatic patients with isolated buttock pain having normal MRI lumbosacral spine.