Piriformis syndrome is due to entrapment of the sciatic nerve by the piriformis muscle. Buttock pain is exacerbated by activities that promote internal rotation of the hip, as the muscle promotes external hip rotation. This entity is unusual, sometimes even controversial, and is difficult to diagnose. Piriformis syndrome should be suspected when more common conditions, such as S1 radiculopathy, sacroiliitis, facet arthropathy and lumbar disk disease, have been excluded by imaging.1 Moreover, MRI of the pelvic girdle is extremely helpful to assist the diagnosis, because it can show structural changes in the muscle,2 as in the present case.
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