Unicystic ameloblastoma - A clinicopathologic study of 33 Chinese patients

The term unicystic ameloblastoma refers to those cystic lesions that show c linical, radiographic, or gross features of a jaw cyst, but on histologic e xamination show a typical ameloblastomatous epithelium lining part of the c yst cavity, with or without luminal and/or mural tumor growth. To ascertain the clinicomorphologic spectrum and biologic behavior of this tumor group, the clinicopathologic features of 33 unicystic ameloblastomas from Chinese patients were studied. This series represents approximately 19% of all cas es of ameloblastoma accessioned in the authors' hospital during a 15-year p eriod. Twenty-one one patients were male and 12 were female, for a total of 33 patients. The age at diagnosis ranged from 8 to 60 years (mean, 25.3 yr s) and peaked at the second and third decades (70%). Thirty tumors (91%) oc curred in the mandible and three in the maxilla. Of the 29 patients with a radiographic record, an expansive unilocular radiolucency was seen in 22 ca ses, and was multilocular in seven cases. Microscopically, all tumors demon strated a generally monocystic growth pattern. Eight tumors were simple cys tic, 10 comprised intraluminal tumor nodules, and the remaining 15 had a co nspicuous component of infiltrative tumor islands in the cyst capsule. The cystic tumor linings invariably showed, at least in part, a typical amelobl astomatous pattern that was often accompanied by epithelial areas of variou s histologic appearance. Follow up of 29 patients revealed no recurrence in less than 4 years of follow up, but did reveal a 35% recurrence rate at mo re than 4 years of follow up. The average interval to recurrence was approx imately 7 years. Recurrence also appeared to relate to histologic subtypes of unicystic ameloblastoma, with those invading the fibrous wall having a r ate of 35.7%, but other types having a rate of 6.7%. Despite the fact that unicystic ameloblastoma may, in general, compare favorably with its solid o r multicystic counterpart in terms of clinical behavior and response to tre atment, the subsets of the maxillary lesions or tumors containing invading islands in the fibrous wall could have a high risk of recurrence. Furthermo re, recurrence of unicystic ameloblastoma may be long delayed, and a long-t erm postoperative follow up is essential to the proper management of these patients.