Fibrous dysplasia is a fibro-osseous lesion where normal bone gets replaced by fibrous tissue and abnormal bone. The exact etiology is unknown but a localized change in bone metabolism can be observed. It can affect a single bone (monostotic) or multiple bones (polyostotic). Polyostotic fibrous dysplasia can be divided into two types: Jaffe type, without endocrine disturbances and part of McCune Albright syndrome (The syndrome consists of polyostotic fibrous dysplasia, café-au-lait spots on skin and endocrine dysfunction such as precocious puberty). If multiple bones in the head and neck region are affected, then it is called craniofacial fibrous dysplasia.
80% of fibrous dysplasia cases that affect the jaws are solitary (monostotic). The common site of involvement is posterior maxilla. Other sites include mandible, long bones, and ribs. There is no sex predilection of fibrous dysplasia except for Albright’s syndrome which solely affects females. Fibrous dysplasia often appears in childhood in multiple (polyostotic) type, and up to 30 years of age for the solitary (monostotic) type. It grows slowly during growth period and generally ceases to grow after the general growth period has ceased. The symptoms are usually swelling, facial asymmetry, malocclusion, and rarely pain when it is impinging or interfering with functions of other vital structures.
Fibrous dysplasia is most often unilateral. It can occur in the mandible; however, it occurs mainly in the posterior maxilla. The radiopaque appearance varies depending on its stages of maturity. In early (osteolytic) stages, fibrous dysplasia appears as a radiolucent lesion. In the intermediate stage, it has a ground glass, fingerprint, or orange peel appearance. In the final (mature) stage, it appears completely radiopaque. Large lesions can cause thinning of the cortex but rarely perforate it. The periphery of fibrous dysplasia is ill-defined and blends with the surrounding normal bone. The margins can appear rarely sharp in younger individuals. Fibrous dysplasia can expand in the maxillary sinus and displace its boundaries. It usually starts from the lateral wall of the sinus and it can grow to occupy most of the sinus space. Most of the time teeth are not affected and the bone surrounding them get changed. Fibrous dysplasia can affect teeth eruption and in rare cases root resorption can occur. Fibrous dysplasia can displace the mandibular canal superiorly.
Metabolic bone disease like hyperparathirodism has characteristics similar to fibrous dysplasia. However, hyperparathoriodism is polyostotic, bilateral and does not cause bone expansion. Although Paget’s disease has similar features to fibrous dysplasia and can cause bone expansion, it differs from fibrous dysplasia in that it affects older age groups and if the mandible got involved; then the whole mandible get affected unlike fibrous dysplasia where it occurs usually unilaterally. Periapical cemental dysplasia can occasionally look similar to fibrous dysplasia but it affects older age groups and occurs bilaterally. It is imperative to differentiate fibrous dysplasia from osteomyelitis and osteogenic sarcoma. Osteomyelitis lays layers of bone from periosteum on its outer cortical surface while fibrous dysplasia expands centrally causing thinning of the cortical surfaces. Osteogenic sarcoma shows malignant features beside features similar to fibrous dysplasia. It is often difficult to differentiate fibrous dysplasia from ossifying fibroma. If there is no displacement of teeth and only the bone surrounding the teeth got affected then it is more likely to be fibrous dysplasia.
In many instances, biopsy is not done as the lesion has specific characteristics enough to differentiate it from other lesions. It is recommended to consulate with an oral and maxillofacial radiologist. Cone Beam CT scan can be used to determine the extension of the lesion and to determine its location to the surrounding structures in three dimensions. Data set from Cone Beam CT can be used for monitoring the progress of the lesion and serves as a baseline. Conservative osseous contouring for cosmetic correction should be delayed until after cessation of skeletal growth. There have been some reports that indicate the possibility for pregnant women and those who take oral contraceptives with fibrous dysplasia can cause the lesion to grow in size or form other lesions such as aneurysmal bone cysts or central giant cell granulomas. Irradiation can be an inciting factor in the development of sarcoma in these patients is highly suggestive..
HISTORY: A 17-year-old male was referred for a Cone Beam CT scan for evaluation for what was found by his orthodontist for a referral for a third molar removal. The patient has a prior history of fibrous dysplasia and fracture of his right femur two years ago. He does have same cafe au lait spots behind his neck.
FINDINGS: There is an ill-defined lesion in the mandible. The lesion exhibit ground glass appearance. There is bucco-lingual that can be seen on clearly on cross-sectional images and it is located approximately between the premolar area in the left mandible and extends to the right ramus area. Diffuse calcifications are noted in the anterior region. Signs of roots resorption or displacement of the mandibular canal are not evident.
IMPRESSION: The radiographic appearance of this lesion is most consistent with fibrous dysplasia.
HISTORY: A 12-year-old male was referred for a Cone Beam CT scan for evaluation of radiopaque expansile lesion of the right anterior mandible.
FINDINGS: There is an irregular but well defined radiopaque lesion in the anterior mandible. The lesion has moderately-defined borders. The lesion has moderately-defined borders. The lesion is expansile and the trabeculation pattern within the lesion exhibits ground glass appearance. The lesion is located approximately between of tooth #21 to #30 and from alveolar crest superiorly to the inferior mandibular cortex inferiorly. There is thinning of the mandibular cortical border anteriorly and more extensively near impacted and inferiorly displaced tooth #27 which has crossed the midline to the other side that shows either little evidence of root formation or significant root resorption. There are retained deciduous teeth (#S and T). Teeth #28-29 are impacted. Cross-secional and axial images shows lingual expansion where the lesion is confluent with cortical bone.
In addition, there are two more radiopaque regions that represent area of focal sclerosis or abnormally dense bone. One of them is located approximately between the right ethmoid and sphenoid sinus and the other one is located at the lateral pterygoid plate.
IMPRESSIONS: The radiographic signs of this lesion are consistent with fibrous dysplasia. The presence of two other radiopaque lesions in the maxilla is highly suggestive of polyostotic fibrous dysplasia.