Fibrous dysplasia is the most common of a group of fibro-osseous lesions that may affect the craniomaxillofacial skeleton. Histologically normal bone is replaced by fibrous and mineralized tissues often containing giant cells.
It is caused by a somatic mutation in utero and it is present at birth, although it is typically detected in the 1st or 2nd decade when it becomes clinically evident.
It may involve one bone or a series of contiguous bones (monostotic) or affect multiple discontiguous bones (polyostotic).
The clinical course is unpredictable but in many patients a period of proliferation in adolescents and early adulthood may be followed by stabilization and non-progression of the disease. Malignant transformation has been reported in 0.5-2% of patients and is heralded by rapid growth and pain.
The lesion is often asymptomatic and slowly progressive with males and females equally affected. The most frequently involved bone is the maxilla, followed by the mandible and frontal bone, although any craniofacial areas might affected.
Clinical features include:
Facial asymmetry due to diffuse expansile growth of the affected facial bones
Proptosis, dystopia and globe displacement; diplopia
Maloclussion (teeth displaced but not otherwise affected)