Ewing Sarcoma, Femur

45-year-old female presenting with left thigh pain and swelling. The images demonstrate an infiltrative T1 isointense to skeletal muscle, STIR heterogeneously hyperintense lesion involving both the medullary cavity and cortical margin of the left femoral diaphysis with extension into the adjacent thigh musculature. The medullary fat within the left femoral diaphysis is no longer present. There is prominent diffusion restriction. The lesion heterogeneously enhances with a centrally necrotic core. A differential diagnosis of osteosarcoma and metastatic disease was given. On biopsy, Ewing sarcoma was found. Clinical presentation is nonspecific with local pain being the most common symptom. A soft tissue mass may or may not be palpable. Pathologic fractures can also occur. Ewing sarcoma falls into the category of small round blue cell tumor. Femur involvement is most common. Systemic chemotherapy is the mainstay of treatment.