Which radiological sign describes a bone tumor that has broken through the cortex and lifted the periosteum, creating a triangular area of new bone formation at the margin of the lesion?

Explanation

## Codman Triangle: Definition and Significance **Key Point:** The Codman triangle is a radiological sign of aggressive bone lesions where the periosteum is lifted by an expanding tumor, and new bone is laid down in a triangular configuration at the margin where the periosteum is still attached to the cortex. ### Pathophysiology When a tumor grows rapidly and breaks through the cortex: 1. The periosteum is elevated away from the bone surface 2. The periosteum attempts to form new bone (reactive response) 3. At the edges where periosteum remains attached, triangular areas of new bone form 4. This creates the characteristic triangular or cone-shaped appearance on radiographs ### Clinical Significance **High-Yield:** Codman triangle is a sign of **aggressive lesions** but is NOT pathognomonic. It indicates: - Rapid growth rate - Cortical breakthrough - Periosteal reaction - Malignancy (often osteosarcoma, Ewing sarcoma) or aggressive benign lesions (osteomyelitis, hemangioma) ### Differential Radiological Signs of Bone Tumors | Sign | Appearance | Associated Lesion | |------|-----------|-------------------| | Codman triangle | Triangular periosteal new bone at lesion margin | Aggressive lesions (osteosarcoma, Ewing sarcoma) | | Sunburst (radiating spicules) | Radiating spicules of new bone perpendicular to cortex | Osteosarcoma (classic) | | Onion skin (lamellated) | Concentric rings of periosteal new bone | Ewing sarcoma (classic) | | Soap bubble | Large multilocular radiolucencies | Giant cell tumor, aneurysmal bone cyst | | Periosteal new bone | Solid, uninterrupted | Benign or slow-growing lesions | **Clinical Pearl:** While Codman triangle suggests aggression, it can also be seen in benign conditions like hemangioma or osteomyelitis. The key is to integrate it with other imaging findings (cortical destruction, soft tissue mass, location) and clinical presentation. **Mnemonic - Aggressive Periosteal Reactions:** **CSOS** - **C**odman triangle - **S**unburst - **O**nion skin - **S**oft tissue mass (indicates malignancy) [cite:Rockwood and Green's Fractures in Adults, Musculoskeletal Imaging Chapter]