Which lesion is associated with radiolucent, extraarticular, geographic appearance?

Which lesion is associated with radiolucent, extraarticular, geographic appearance?

• A. Osteomyelitis
• B. Osteosarcoma
• C. Ewing sarcoma
• D. Unicameral bone cyst

Answer: (D)

A radiolucent, geographic, extraarticular lesion points to a benign, contained cavity typical of a unicameral bone cyst. These lesions are most common in children and occur in the metaphysis of long bones, often near the growth plate. The key features are a single cavity (unicameral), a well-defined, smooth border, and a radiolucent appearance with a thin surrounding sclerotic rim. Because the lesion is well circumscribed and contained away from the joint, it is described as extraarticular and geographic, meaning the border is clearly defined rather than diffuse or permeative.

Other conditions tend to disrupt these features: osteomyelitis often presents with more irregular, ill-defined margins and may show sequestrum or involucrum; osteosarcoma and Ewing sarcoma typically show more aggressive patterns with mixed lytic-sclerotic changes, periosteal reactions, and less well-defined borders. The combination of a single, clearly defined radiolucent cavity in the metaphysis of a child’s long bone best matches a unicameral bone cyst.