Aneurysmal bone cyst of the paranasal sinuses associated with fibrous dysplasia: CT and MR findings.

An aneurysmal bone cyst (ABC) in the paranasal sinuses is rare with only four previous cases having been described in the sphenoid and ethmoid sinuses. This report describes a case of an ABC involving the sphenoid and ethmoid sinuses as well as the upper nasal fossae. It is currently believed that a preexisting primary bone lesion, such as fibrous dysplasia, initiates an osseous arteriovenous fistula, which creates a secondary reactive lesion of bone, the ABC. These lesions, which are comprised of multiple cysts containing liquid blood and serous fluid, are optimally studied by a combination of CT and MR scans.