Ewing's sarcoma of the hip presenting as a benign cystic lesion.

A 14-year-old girl with a Ewing's sarcoma of the left femoral head and neck is presented. The imaging features mimicked a benign cystic lesion. Biopsy and molecular analysis confirmed the diagnosis. The patient was treated with chemotherapy, wide tumor resection, and proximal femoral reconstruction using an allograft-prosthesis composite. Differential diagnosis, imaging, and pathologic features of Ewing's sarcoma are discussed.