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Abstract
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.