Codman triangle (previously referred to as Codman's triangle) is a term used to describe the triangular area of new subperiosteal bone that is created when a lesion, often a tumour, raises the periosteum away from the bone. [1] A Codman triangle is not actually a full triangle. Instead it is often a pseudotriangle on radiographic findings with ossification on the original bone and one additional side of the triangle which forms a two sided triangle with one open side. This two sided appearance in generated due to a tumor (or growth) that is growing at a rate which is faster than the periosteum can grow or expand, so instead of dimpling, the periosteum tears away and provides ossification on the second edge of the triangle. [2]
The main causes for this sign are osteosarcoma, Ewing's sarcoma, eumycetoma, and a subperiosteal abscess.[1]
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