Ewing Sarcoma (ES)/Primitive Neuroectodermal Tumor (PNET)
The most common sites of involvement are medullary cavity of long tubular bones (femur, tibia, humerus, fibula), flat bones of pelvis, vertebra, ribs, and clavicle. Radiographs show a destructive lesion with widening of medullary cavity. Reactive periosteal bone deposits perpendicular to the cortex (sun-ray appearance) are present mid-shaft in this image. When deposited in a concentric fashion, it creates an onion-skin appearance.