Massive chondroid differentiation in fibrous dysplasia of bone (fibrocartilaginous dysplasia).

Eight cases of fibrocartilaginous dysplasia (fibrous dysplasia with massive cartilaginous differentiation) of bone are reported. The age of the patients ranged from 4 to 26 years, with an average of 17.5 years. The male/female ratio was 1:1. In two patients the lesions occurred in a setting of polyostotic fibrous dysplasia. The anatomic sites most frequently affected were the femur and tibia. The proximal femur was the most common site. Roentgenograms showed well-demarcated lucent lesions of ground-glass opacity. In addition, stippled or ring-like calcifications suggesting cartilaginous elements were seen in six cases. Histologically, hyaline cartilage islands were found in juxtaposition to a fibro-osseous lesion characteristic of fibrous dysplasia. Enchondral ossification was commonly seen, frequently showing columnar arrangement of cartilage cells mimicking a growth plate. The cartilage may show moderate atypism. The important thing is to recognize the benign nature of chondroid elements in fibrous dysplasia. Even if cartilage dominates the histologic picture, it is important to identify the fibro-osseous elements and thereby avoid the misdiagnosis of chondrosarcoma.