Scintigraphic diagnosis of myositis ossificans

A 28 year old female presented with a complaint of swelling associated with pain in the lateral aspect of lower right thigh for one month. At two weeks from onset she consulted a local practitioner who attempted an incision and drainage of the swelling. The symptoms aggravated further and she developed low grade fever as well. She gave a history of blunt injury to the affected region eight years back without any complication. Local examination revealed a mass of 5 cm x 5 cm size, soft in consistency, mobile with ill-defined borders. Swelling was not easily palpable on contraction of the muscles. ESR and total leukocyte count was high. Three phase bone scintigraphy revealed a focus on lateral aspect and adjacent to the right femur with intense radiotracer concentration in all three phases.

A diagnosis of heterotopic ossification was suggested. X-ray revealed an oval radioopacity in the soft tissue adjacent to the shaft of the right femur. The cortex of the femur was intact. Ultrasound showed a well defined thick walled cystic lesion in the substance of right vastus lateralis muscle. Mass was excised. Histopathology revealed features suggestive of myositis ossificans. Intense radiotracer uptake is due to the osteoid tissue present in the lesion.