Cemento-ossifying fibroma of the ethmoidal sinus manifesting as proptosis.

We report an aggressive cemento-ossifying fibroma of the ethmoidal sinus that initially manifested as proptosis and was misdiagnosed as meningioma after a frozen section was tested. Fibroosseous lesions containing cementum are considered to be of periodontal membrane origin and are most common in the mandible and maxilla. With the exception of the gigantiform cementoma, they are usually small, innocuous lesions following a benign course and are easily removed surgically. On rare occasions, the cemento-ossifying fibroma attains a large size, behaves aggressively, destroys bone, and requires radical surgery for complete excision. Such behavior appears likely when is is located in unusual sites such as the ethmoidal sinus. To our knowledge, our case is the third report of a cemento-ossifying fibroma arising in the ethmoidal sinus. Aggressive behavior has been a feature in all three instances.