What is Codman's triangle and how has its interpretation evolved?

• A. Triangular periosteal reaction generally at lesion margin; historically pathognomonic for osteosarcoma but is nonspecific
• B. Triangular lesion only seen in benign conditions
• C. A sign always diagnostic of osteosarcoma
• D. A sign of infection only

Answer: (A)

Codman’s triangle is a radiographic sign of an aggressive periosteal reaction. It occurs when rapid growth of a lesion lifts the periosteum away from the bone cortex, and new bone forms along the elevated periosteum, creating a triangular wedge at the edge of the lesion. Historically this feature was considered highly suggestive of osteosarcoma, but it is not specific to that disease. Any fast-growing process that irritates the periosteum—such as other malignant bone tumors, osteomyelitis, metastasis, or even trauma—can produce a Codman’s triangle. The modern interpretation emphasizes that its presence indicates an aggressive lesion but does not diagnose osteosarcoma by itself; accurate diagnosis relies on clinical context and often histopathology.