What is the characteristic imaging appearance of an osteochondroma?

The characteristic imaging appearance of an osteochondroma is a mushroom-shaped mass. Osteochondromas are benign bone tumors that typically present as bony protrusions from the surface of the bone, often seen in the metaphysis of long bones, particularly around the knee. On imaging, these lesions can be identified by their distinct appearance resembling a mushroom or a cauliflower, with a cartilage-capped surface that can occasionally show signs of calcification.

This defining shape is due to the periosteal bone growth that occurs when the growing bone forms a projection. Imaging modalities, such as X-rays, often reveal this characteristic morphology clearly, making it a diagnostic hallmark for osteochondroma. In contrast, the other options represent features associated with different conditions or tumors: onion skinning is typically seen in conditions such as osteomyelitis or certain types of sarcomas, the sunburst pattern is indicative of osteosarcoma, and ground glass appearance is often associated with fibrous dysplasia. Understanding these distinctions is crucial for accurate diagnosis and appropriate management of skeletal tumors.