General Medical Information

Benign Tumors Of Bony Origin

Barbara A. Zeifer

Benign bone tumors of the paranasal sinuses are of fibroosseous or of giant cell origin. Fibroosseous lesions include osteoma, osteochondroma, ossifying fibroma, and fibrous dysplasia. Giant cell lesions include giant cell granuloma and brown tumor. Osteoma, a common lesion, is benign proliferation of mature bone. It occurs almost exclusively in the head and neck, particularly in the frontal and ethmoidal sinuses. Compact osteoma and ivory osteoma are seen as extremely dense, well-defined masses within the paranasal sinuses. Cancellous osteoma is variable in density on plain radiographs and CT because of the presence of a fibrous component. They can even appear as a soft-tissue density on plain radiographs, but CT shows the ossific character. Multiple osteomas of the face and skull are one of the many manifestations of Gardner syndrome. Osteochondroma can occur in the nose and paranasal sinuses. As in other locations, it is heterogeneously calcified and is pedunculated.

Fibrous dysplasia has a wide range of radiographic appearances that depend on the relative amounts of fibrous and osseous tissue within the lesion. Head and neck involvement is quite common, occurring in 50% of cases of polyostotic and in 10% to 15% of cases of monostotic disease. Any sinus can be involved. These lesions are nondestructive, causing thickening and enlargement of the involved bone, which often maintains its original shape. Most lesions have a hazy ground-glass appearance. Cystic and sclerotic lesions are less common. Lesions become more sclerotic with age. The MRI appearance of fibrous dysplasia can be confusing. During T1 sequences, signal intensity ranges from mildly hyperintense to hypointense. Mild-to-moderate enhancement is common. On T2-weighted images, marked, homogeneous hypointensity is seen throughout the lesion, with the exception of cystic areas. This finding confirms the diagnosis.

Ossifying fibroma is closely related to fibrous dysplasia and tends to involve the facial bones. It typically has a greater soft-tissue component and a more aggressive appearance than does fibrous dysplasia, but often the two cannot be differentiated. These lesions are well-circumscribed, expansile masses that can be of homogeneous soft-tissue density, densely sclerotic, or of mixed attenuation on CT scans.

Brown tumor of hyperparathyroidism is the most common giant cell lesion of the facial bones. These lesions produce unilocular or multilocular cystic, expansile masses with well-defined margins. After treatment and healing, brown tumor becomes quite dense. While often it cannot be differentiated from brown tumor; giant cell granuloma can be an aggressive lesion, at times mimicking a malignant tumor. Giant cell granuloma usually is located in the anterior aspect of the mandible or maxilla and contains calcific, ossific, or osteoid components in 30% to 75% of cases.