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Fibrous dysplasia  

Fibrous dysplasia is due to an abnormality in the development of bone-forming mesenchyme. The spongy bone is replaced by a peculiar fibrous tissue in which trabeculae of poorly calcified nonlamellar bone are formed by osseous metaplasia. Patients may have a small solitary focus, the monostotic form or may have many bones affected with multiple lesions, the polyostotic form. Swelling is unilateral and painless. The radiographic appearance is extremely variable. Three types of basic patterns may be seen. In the first type, the lesion is generally a rather small unilocular radiolucency or a somewhat larger multilocular radiolucency, both with a rather well-circumscribed border; a network of fine bony trabeculae may be seen within the lesion. In the second type, the pattern is similar except that increased trabeculations render the lesion more opaque and typically mottled in appearance. The third type is quite opaque, with many delicate trabeculae, giving a ground glass or peau d’orange (orange peel) appearance to the lesion. This type is not well circumscribed, but blends into the adjacent bone. Ground glass opacification results from the superimposition of a myriad of poorly calcified bone trabeculae arranged in a disorganized pattern. Orange peel appearance with stippling is seen in some cases. Lamina dura of teeth in the affected area may be lost. This is quite common in the maxilla.
When the mandible is affected, its vertical depth is increased. Fibrous dysplasia may displace the mandibular canal superiorly, which is a significant finding in differentiating this disease from other fibro osseous lesions of the mandible, as most of the other lesions in this group develop above the canal and close to the dental structures. The ribbon-like cortex at the inferior border of mandible is partially or fully lost. Over the site of lost cortex, there may be a smooth curved projection downward. The appearance resembles a thumbprint as if bone had been soft and pressed upon by the thumb. This appearance is pathognomonic of fibrous dysplasia.

CT characteristics of fibrous dysplasia include expansion of the involved bone with heterogeneous pattern of CT densities associated with scattered or confluent islands of bone formation. Surgical correction is necessary for functional reasons and for disfigurement. Though it is rare, sarcoma, especially osteogenic sarcoma, may arise in these lesions.

Image	Caption
	Figure 1: Occlusal view of a patient with fibrous dysplasia.
	Figure 2: Fibrous dysplasia. Facial asymmetry in a woman with fibrous dysplasia of the right maxilla.
	Figure 3: Intraoral photograph of the same patient showing buccal expansion with obliteration of the buccal sulcus in the right maxillary premolar region. Note the edentulous area in the second molar region showing indentation of lower molar teeth.
	Figure 4: Panoramic radiograph of the same patient showing diffuse radioopacity in the right maxilla with a ground glass appearance.