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The radiographic changes, the clinical behavior of expansion and the age of the patient are all consistent with fibrous dysplasia. Although the location is unusual for FD, it can still be included on the differential diagnosis. The histology is supportive of FD.
The etiology of fibrous dysplasia is unknown. The monostotic (one bone or bone complex area) form makes up approximately 80% of all fibrous dysplasia cases; the polyostotic form affects one or more bones with multiple lesions. FDs are expansile and disfiguring lesions, whether single or multiple, which differentiates them from the usually flat osteomas of Gardner's syndrome. Monostotic FD, which involves the jaws, affects males and females equally. It occurs in childhood and at puberty and usually stops growing at age 30. It appears as an asymptomatic swelling of the maxilla or mandible; maxillary lesions are the most common. It may involve bones other than the maxilla, such as the zygoma and the sphenoid. It is usually unilateral and is known to displace the teeth, but otherwise is firmly seated. The growth is usually slow, but rapid growth has been described, especially during puberty. The radiographic appearance, especially of the maxilla, is classically described as a ground glass appearance where fine radiopacity is noted. The mandibular lesions are much more deceptive because they tend to vary more, thus making diagnosis with a radiograph difficult. They may consist of a cystic unilocular radiolucency, multilocular radiolucency, or the classical ground glass radio-opacity. Treatment may be necessary and is preferably performed after cessation of growth due to the high incidence of re-growth and requirement for secondary procedures. Radiation therapy is contraindicated since significant incidence of development of osteosarcoma in the irradiated bone has been documented. Malignancies such as osteosarcoma arising in an area of FD that has not been irradiated have been described, but rarely; these occur mainly in irradiated lesions. The overall prognosis is good with close follow-up.