MRI depends upon the age of the lesion. Surrounding edema may be seen in lesions less than a few months old. In T1-weighted images, only mass effect may be noted with displacement of fascial planes. Bone scintigraphy reveals enhanced uptake in immature lesions. Once maturation occurs, uptake becomes comparable with normal bones.
Ultrasound examination shows echogenic and shadowing mass.
Once diagnosis is established, further biopsy of additional lesions is contraindicated in myositis ossificans progressiva. In nonhereditary myositis ossificans, perform a biopsy primarily to exclude osteosarcoma. At least 10 days are required following onset of symptoms for these zones to become apparent. If the biopsy is performed before 10 days have elapsed, or if a biopsy sample is obtained from the central region, the specimen yields undifferentiated tissue resembling an osteosarcoma. In contrast to osteosarcoma, myositis ossificans exhibits a zonal pattern, the lesion has viable muscle fibers, and myositis ossificans does not invade surrounding tissue.