Recently, gene mutations have been delineated that cause inappropriate proliferation and differentiation of osteoblasts resulting in the production of the fibrotic bone matrix seen in both monostotic and polyostotic fibrous dysplasia. The cells and matrix of fibrous dysplasia lesions have been shown to produce an abnormal complement of bone matrix proteins. In light of these developments, dysplastic lesions are thought to consist of an excess of pre-osteogenic cells producing a disorganized collagenous matrix. The few mature osteoblasts present create abnormal bone matrix. The radiographic findings of fibrous dysplasia can be distinctive.
Individual lesions can appear as a lucent area with a sclerotic rim.
The affected bone can be locally expanded. Calavarial lesions are usually lytic and multilocular with sclerotic margins. In the skull base and facial bones, fibrous dysplasia manifests as marked sclerosis and bony thickening. The sinuses may be obliterated. Long standing disease can result in bowed and deformed bones.