Fibrous Dysplasia

Fibrous dysplasia is another osteodystrophy or developmental disturbance of bone formation and is also discussed in Chapter 21. In fibrous dysplasia, bone is resorbed and then replaced with haphazardly arranged fibrous tissue. Fibrous dysplasia is classified as monostotic, polyostotic, or McCune-Albright syndrome. McCune-Albright syndrome is a polyostotic fibrous dysplasia along with endocrine abnormalities consisting of skin changes over the neck and trunk, precocious puberty, accelerated skeletal growth, hyperparathyroidism, acromegaly, hyperthyroidism, Cushing's disease, and diabetes mellitus.

The etiology of fibrous dysplasia is unknown and there is a small incidence of malignant transformation into osteosarcoma. Usually, the disease starts within the first decade of life and stabilizes after puberty. The disorder typically presents as a painless bony growth involving the face or skull. Facial asymmetry may be present with variable progression to gross deformation commonly seen.

Neuropathy has been well described and is due to direct compressive effects of the abnormal bony remodeling. When the temporal bone is involved, the most common clinical manifestations are external auditory canal stenosis and conductive hearing loss. Although optic neuropathy is more frequent, facial paralysis has also been associated with fibrous dysplasia. Facial palsy has been reported in 9% of patients with temporal bone involvement (121).

Diagnosis is confirmed by characteristic bony lesions on radiographs that appear as "ground glass" with a cortex that is always intact. Histopathologic features consist of immature woven bone arranged in "Chinese character" appearance from the fibrocolla-genous cellular spindly stroma and is considered pathognomonic for the disease. There is no known medical treatment for this disorder and patients typically undergo conservative surgical bony remodeling procedures. Facial paralysis from mechanical compression of the nerve by abnormal bony remodeling is treated by surgical decompression of the nerve.

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