Extraskeletal osteosarcoma arising in myositis ossificans: a case report and review of the literature.

We report a case of a 23-year-old female with pain and fullness in the right popliteal fossa. An MRI scan demonstrated an ossified enhancing soft tissue mass. Evaluation of the resected specimen showed a high-grade extraskeletal osteosarcoma juxtaposed to the three zones of myositis ossificans. At 1-year follow-up the patient is alive and disease free. A review of the literature purporting to document such an association failed to demonstrate a single case in which an osteosarcoma and MO with its zonal architecture co-existed.