Ewing's sarcoma tends to involve which portion of long bones?

• A. Middle of long bones
• B. End of long bones
• C. Epiphysis only
• D. Throughout the entire bone

Answer: (A)

Ewing's sarcoma most often begins in the diaphysis, the shaft or middle portion of long bones. It originates in the medullary cavity in children and adolescents and tends to expand from the midshaft outward, making the midportion the typical site. Clinically this presents with localized bone pain and swelling, and imaging frequently shows a layered periosteal reaction described as onion-skin, which reflects rapid tumor growth in the marrow and periosteum. Because the tumor starts in the diaphysis, involvement of the end portions (epiphyses) or a lesion later spreading throughout the entire bone is less characteristic at presentation. Thus, the middle portion of long bones is the best answer.