Ewing's sarcoma of the pelvis: an unusual, but not to be missed, cause of an irritable hip.

A 15-year-old girl presented with a 2-month history of non-specific right hip pain associated with pain in the back, right flank and foot. Her symptoms deteriorated, interfering with weight-bearing. Following admission, she was found to be febrile with a flexion deformity of her right-hip, and tenderness over the iliac crest and posterior pelvis. A markedly elevated C reactive protein and erythrocyte sedimentation rate, with an ultrasound-proven scan effusion within the right hip were all suggestive of septic arthritis. However, full blood count demonstrated a significant anaemia, which together with the tenderness around the pelvis was not in keeping with this diagnosis. Surgical washout was therefore delayed to obtain a MRI scan of the pelvis. The scan revealed a 5×5×3 cm necrotic soft tissue mass within the gluteal muscles, arising from the right ilium, which biopsy confirmed to be a Ewing's sarcoma.