Hip pain in an adolescent.

We have described a case of osteomyelitis of the ischium with extension into the adjacent soft tissues and abscess formation. Diagnosis and treatment were initially delayed due to the assumption that edema in the thigh muscles seen on initial MRI represented polymyositis. Subsequent radiographs demonstrated a destructive lesion containing a sequestrum within the ischium, indicative of osteomyelitis. It was, however, the MRI imaging that dramatically demonstrated the full extent of the complicating abscess which extended downward to mid-thigh and upward under the gluteal muscles almost to the top of the iliac crest. This proved to be an invaluable guide for the surgeon.