[Fibrous dysplasia and ossifying fibroma. Morphologic criteria]

Among a series of 42 ossifying fibromas and 32 fibrous dysplasias, 5 cases were studied by histoenzymological and electron microscopic methods. The histological study in 2/3 of cases is sufficient for the diagnosis between the two diseases: trabecular bone in a connective tissue with regular collagen fibres in the ossifying fibroma; nodular indented bony areas with irregular collagen frame in fibrous dysplasia. By histoenzymology, the diagnosis between the two affections is not easy: same activity of ATPases and alkaline phosphatases in fibroblasts and osteoblasts. By electron microscopy, the morphology of the two lesions is different: in ossifying fibroma, numerous well-differentiated osteoblasts and large areas of ossification are seen; in fibrous dysplasia, undifferentiated cells are numerous and the collagen frame is irregularly mineralized. This method is also useful for the histogenetic understanding of these two osteopathies.