Which radiographic feature is a buzz word for Ewing sarcoma?

• A. Parallel
• B. Spiculated
• C. Onion-skin periosteal reaction
• D. Hair on end

Answer: (D)

The main concept is recognizing the onion-skin periosteal reaction as the radiographic hallmark of Ewing sarcoma. This layered, concentric new bone formation occurs when the periosteum repeatedly reacts to tumor growth, lifting away and laying down multiple thin sheets of new bone. In children and teenagers, Ewing often involves the diaphysis of long bones and can be accompanied by a soft-tissue mass and a permeative lesion on X-ray, which together reinforce this diagnosis. Other options don’t fit as well: spiculated (sunburst) patterns point more toward osteosarcoma; hair-on-end describes a pattern seen in certain anemias and other conditions, not classic for Ewing; parallel isn’t a recognized periosteal reaction pattern. Therefore, onion-skin periosteal reaction is the best descriptor for Ewing sarcoma.