Unicystic ameloblastoma. A review of 193 cases from the literature.

Based on a world-wide literature survey of 193 published cases of unicystic ameloblastomas (UA), data have been produced allowing the presentation of a revised concept of this much debated lesion. UA is a variant of the solid or multicystic ameloblastoma. Radiographically, the unilocular pattern is more common that the multilocular, especially in cases associated with tooth impaction. However, it is stressed that although the lesion is pathomorphologically unicystic, it will far from always produce a unilocular radiolucency. The mean age at the time of diagnosis of UA is closely related to an association with an impacted tooth. Almost 20 years separate the mean age of the 'dentigerous' variant from the 'non-dentigerous' (16.5 years versus 35.2 years) The male:female ratio for the 'dentigerous' type is 1.5:1, but for the 'non-dentigerous' type it is reversed (1:1.8). Location favours greatly the mandible (mandible to maxilla = 3 to 13:1). Between 50 and 80% of cases are associated with tooth impaction, the mandibular third molar being most often involved. The 'dentigerous' type occurs on average 8 years earlier than the 'non-dentigerious' variant. The mean age for unilocular, impaction-associated UAs is 22 years, whereas the mean age for the multilocular lesion unrelated to an impacted tooth is 33 years. Histologically, the minimum criterion for diagnosing a lesion as UA is the demonstration of a single cystic sac lined by odontogenic (ameloblastomatous) epithelium often seen only in focal areas. This simple type of UA (according to the authors' modification of the classification by Ackermann et al. (Journal of Oral Pathology 1988; 17:541-546)), is one of four UA subtypes, the others being (1) simple with intralumenal proliferations; (2) simple with both intralumenal and intramural proliferations; and (3) simple with intramural proliferations only. All four subtypes occur in both the 'dentigerous' and 'non-dentigerous' variants. The simple subtype with and without intralumenal proliferations may be treated conservatively (enucleation), whereas subtypes showing intramural growths must be treated radically, i.e. as a solid or multicystic ameloblastoma. Finally, the authors disclose areas and issues pertaining to UA that still need to be addressed.