Head and Neck Imaging

Fibrous dysplasia, head and neck

condition in which normal medullary bone is replaced by an abnormal proliferation of fibrous tissue, resulting in asymmetrical distortion and expansion of bone; it may be confined to a single bone (monostotic fibrous dysplasia) or involve multiple bones (polyostotic fibrous dysplasia). For a general description, see fibrous dysplasia.

The monostotic form may involve any of the facial bones, but is most commonly seen in the maxilla. The association of the polyostotic form with sexual precocity and cutaneous pigmentation in a female patient is known as McCune Albright syndrome.

Fibrous dysplasia is a disease of young patients. It may be an incidental finding. In the maxilla it usually presents with swelling and deformity of the cheek, but sometimes it causes nasal obstruction and/or orbital symptoms. Fibrous dysplasia may give rise to a mucocele. Involvement of the skull base may cause neurovascular compression. Extensive involvement of the face is referred to as leontiasis ossea.

Usually no new lesions appear after the cessation of skeletal growth. The lesions become more sclerotic with time but may continue to grow slowly into adulthood. Occasionally, reactivation of the lesions occurs during pregnancy.

Aggressive clinical behaviour of maxillary fibrous dysplasia has been described, causing pain and rapid development of a mass, although histopathological examination shows typical findings of fibrous dysplasia without evidence of malignancy. However, secondary malignant degeneration into a sarcoma (0.5% of cases) should be considered when stable or recurrent fibrous dysplasia produces pain or soft tissue extension.

Radiologically, fibrous dysplasia appears as enlarged bone with a dense ground-glass appearance (Fig.1); sometimes the lesions have a more osteolytic appearance, with regions of more dense calcification within them (Fig.2). On MRI, the lesions usually have a low to intermediate signal intensity on all sequences, with marked contrast enhancement; incidentally found fibrous dysplasia may be confused with a neoplastic lesion on an MR study (Fig.3).

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Fig.3

Patient presenting with episodes of visual disturbances. On an axial T1-weighted brain spin-echo image, an enhancing mass lesion is seen in the sphenoid sinus (a, arrow), initially suspected to correspond to a neoplastic lesion. Coronal CT image shows the typical ground-glass appearance of fibrous dysplasia (b, arrow).
Fibrous dysplasia, head and neck, Fig.1
Fibrous dysplasia, head and neck, Fig.2
Fibrous dysplasia, head and neck, Fig.3 (a)
Fibrous dysplasia, head and neck, Fig.3 (b)