Fibro-osseous lesion with calcified spherules (cementifying fibromalike lesion) of the tibia.

The histologic and ultrastructural features of a tibial lesion strongly resembling cementifying fibroma of the jaws are described. Histologically the lesion consisted of fibrous tissue containing small calcified spherules. In some areas acellular trabeculae or islets with lobulated margins of a cementlike substance occurred. Spherules and small calcified bodies were composed of apatite crystal depositions along the collagen fibers and were often in close contact with membrane-surrounded cytoplasmic processes resembling matrix vesicles. In fibrous tissue fibroblasts, myofibroblasts, and undifferentiated cells with numerous cytoplasmic processes and intracytoplasmic microfibrils were present. The character of the cellular component of this lesion and the presence of calcified spherules arranged in a manner rarely observed in fibrous dysplasia indicate a histogenic relationship between the two lesions.