Cystic expansile masses of the maxilla: differential diagnosis with CT and MR.

PURPOSE To describe the CT and MR findings of various entities causing cystic expansile masses in the maxilla and the significance of the cortical bony plate between the lesions and sinus cavities in the differential diagnosis. METHODS CT findings of 28 patients with cystic expansile masses of the maxilla, including 20 cases of maxillary mucoceles (17 postoperative mucoceles, 2 mucoceles of a septated compartment of the maxillary sinuses, and 1 maxillary antral mucocele with inflammatory ostial obstruction), 3 cases of fissural cyst, 4 cases of odontogenic cyst, and 1 case of maxillary cystic ameloblastoma, were reviewed. Six cases (4 postoperative mucoceles and 2 odontogenic cysts) were also examined with MR. RESULTS A thin bony plate between the lesion and antral cavity was demonstrated in every extraantral lesion (ameloblastoma, fissural cysts, and odontogenic cysts) and distinguishing these abnormalities from the antral lesions (mucoceles). All mucoceles showed findings of antral lesions except 2 cases of mucoceles at the septated compartments of the sinuses, in which thin bony septa were identified between the lesions and remaining sinus cavities. Postoperative mucoceles showed hyperostotic and retracted bony walls caused by previous surgery and localized erosion of bony walls with localized bulging of the cystic masses in every case. CONCLUSION In the differential diagnosis of cystic masses of the maxilla, careful identification of the bony walls of the antrum and bony septa may allow one to locate the origin of a mass as antral or extraantral. This is important to an appropriate differential diagnosis.