Myositis ossificans: diagnostic value of arteriography.

Myositis ossificans circumscripta is the heterotopic formation of nonneoplastic bone and cartilage in soft tissue. These benign lesions can mimic more serious lesions, both radiographically and histopathologically. Recognition of the benign character of myositis ossificans is imperative in order to avoid mutilating surgical procedures. Five cases are presented with emphasis on angiographic signs which differentiate this lesion from histopathologically similar lesions. Three of these are illustrated, along with an example of an osteosarcoma for comparison. The angiographic manifestations of myositis ossificans differ in the various phases of the disease. In the active stage, the lesions have numerous fine vessels causing a diffus stain. Malignant tumors such as osteosarcoma, extraosseous osteosarcoma, and fibrosarcoma, which are included in the differential diagnosis, often present clearly defined pathologic vessels as well as arteriovenous shunts, venous lakes, amputated vessels, invasion of large arteries and veins, and large abnormal draining veins. In the healing stage, the lesions are usually avascular, and there is no difficulty in differentiating this condition from malignant bone lesions with the sole exception of well differentiated parosteal osteosarcomas. In these cases, the plain radiographic features are most important in arriving at the correct diagnosis.