Extraskeletal retroperitoneal osteosarcoma probably arising from myositis ossificans.
D005260:Female; D006801:Humans; D008875:Middle Aged; D009221:Myositis Ossificans / Q000150:complications*; D012516:Osteosarcoma / Q000473:pathology*; D011859:Radiography; D012186:Retroperitoneal Neoplasms / Q000000981:diagnostic imaging / Q000209:etiology* / Q000473:pathology