Review Question - QID 2851

This patient's history is very benign, but the imaging and histology suggest a high grade osteosarcoma. Based on the images, periosteal osteosarcoma is the correct choice. Periosteal osteosarcomas occur on the surface of the bone, most commonly on the femur and tibia and they typically grow in a "sunburst" fashion creating enlarging, linear matrix ossification. In contrast, parosteal osteosarcomas show a "stuck-on" appearance, and frequently show lower-grade histology (illustration A). Osteochondromas have a characteristic continuation with the medullary canal and do not appear aggressive either on xray or pathology. Dedifferentiated chondrosarcomas develop from previous cartilage tumors and as such have a characteristic appearance on pathology. Synovial sarcoma is a soft tissue sarcoma which can calcify and occur around joints, but has a spindle cell pathologic appearance. The cited references describe these key differences which can all occur around joints, show matrix, but have specific differences.