7 year old with conventional (intramedullary high-grade) osteosarcoma of the femur.

X-ray shows an aggressive bone lesion with Codman’s triangles and extension into the adjacent soft tissues.

MRI shows the full extent of the tumor much better - it is involving the full thickness of the femur, has much further soft tissue extension than suggested by the Codman’s triangles, and even extends into the soft tissues on the other side.