A case of Pseudomalignant myositis ossificans in the psoas muscle.

Abstract

Circumscribed non-neoplasitc heterotopic bone formation without a history of trauma is termed pseudomalignant myositis ossificans. Confusion of myositis ossificans with sarcoma is most likely with small or minute biopsy specimens taken during the early stage of the disease. A seven-year-old boy was presented with a painfull and tender mass of the left psoas muscle with no history of injury. The specimen, which was taken at 2week after the onset in another hospital, was misinterpreted as sarcoma. He was referred to our hospital and anticancer chemotherapy was begun. The mass was excised together with surrounding helthy tissue after 5 months, it was outwardly bony and 5×4×3cm in size. Histologically, a characteristic zone pattern of peripheral bone maturation was presented, so pseudomalignant myositis ossificans was diagnosed.