Two cases of myositis ossificans in children, after prolonged immobilization

Abstract

Myossitis ossificans (MO) is a benign disorder characterized by heterotopic bone formation in skeletal muscle. It is divided in three types, fibrodysplasia ossificans progressive (FOP), myositis ossificans circumscripta or traumatica (MOT) and myositis ossificans without a history of trauma (non traumatic or pseudomalignant MO). Myositis ossificans is extremely rare in children younger than 10 years. We present the clinical and radiological findings of two 5-year-old children with pseudomalignant MO due to prolonged immobilization. Plain x-ray films and CT scan with their characteristic findings of mature bone in the periphery of the lesion with smooth contour and well separated from the bone, enabled us to diagnose the lesion. To the best of our knowledge, no such cases have been reported in the literature.

Figure 1

Radiographs of the pelvis show ossifying masses in the soft tissues projecting over the acetabulum, head and neck of both femurs. The lesions are more extensive on the right side. The periphery of the ossifying masses is denser than the center, an indicative finding of myositis ossificans.

Figure 2

Anteroposterior and frog-lateral projection of both hips reveal extensive heterotopic ossification in the soft tissues adjacent to the medial and lateral cortex of the femoral head and neck on both sides mainly on the right.

Figure 3

Axial and coronal CT reconstruction images of the pelvis demonstrate shell-like ossifications in the quadratus femoris, obturator internus and gluteus muscles on both sides especially on the right. These appearances are compatible with a diagnosis of myositis ossificans.

Figure 4

Follow up CT scan after 8 months shows considerable improvement regarding the extent of the heterotopic bone formation and further absorption of the ossified lesions.