Ameloblastoma is classified as a benign, locally-infiltrative odontogenic neoplasm, which is composed of proliferating odontogenic epithelial nests within a fibrous stromal tissue. Some variants have been subclassified as follows: solid/multicystic, extra osseous/peripheral, desmoplastic, and unicystic . Odontogenesis is a complex biological process, and this process is directly reflected in the development of odontogenic neoplasms, especially ameloblastomas. It is thought that the above-mentioned variants are due to the developmental complex system [4, 5].
Intraosseous small ameloblastomas that sometimes appear within the jawbone are not well-studied. The lesions are not clinically detected; therefore, clinical-oriented evidence is limited at present . In the literature, there has been some discussion on the cellular sources of unsuspected small ameloblastoma arising in the jawbone. Furthermore, the oriented histogenesis is sometime discussed. Houston et al. (2007)  reported a case of ameloblastoma arising from dentigerous cyst With regards to the neoplastic or atypical proliferative change from the lining epithelium of an odontogenic cyst, Antoh et al. (1993)  described such an example in a case of radicular cyst. Careful follow-up is necessary after treatment, since some cysts have the possibility of neoplastic transformation.
As mentioned previously, unsuspected ameloblas tomas are usually small, asymptomatic and confined to the alveolar bone [6, 8]. Their radiographic appearance is usually that of a nondescript lytic lesion. None of these features were observed in the current case. Instead, the case presented as an expansive fluctuant swelling associated with pain and a discharging sinus when the patient attended the Oral Surgery Clinic in January 2007. Radiographically, a unilocular lesion straddling the bone area between the right mandibular lateral incisor and first premolar was observed. Ameloblastoma remained unsuspected at this stage possibly because the clinical and radiological findings were nonspecific and could fit in a variety of inflammatory, neoplastic or cystic conditions of the jawbone.
With regards to the current case, the precise relationship between the radicular cysts enucleated from the right mandibular premolar-molar region in 2006, ameloblastoma diagnosed in the right mandibular canine region in January 2007, and follicular ameloblastoma in the right premolar-molar region in August 2008 remains an enigma. It is likely that the ameloblastoma located in the right mandibular canine and premolar-molar regions are one and the same lesion. Although plain radiographs showed a bony septa separating the two lesions, cancellous spread not detectable on plain radiographs may have occurred. The link, if any, with the radicular cysts that preceded the diagnosis of ameloblastoma in the right mandibular premolar-molar region is also unclear. Evaluation of the past dental history of this case showed that the first lesion diagnosed histopathologically was an apical inflammatory odontogenic cyst (radicular cyst) and this was removed a few times. In January 2007, the lesion enucleated from the right mandibular canine region was histopathologically examined and diagnosed as a cystic ameloblastoma. In consideration of the close proximity of the ameloblastoma in the site where the radicular cysts were previously enucleated. We therefore speculated that this case possibly represented an example of ameloblastoma arising from a cyst. We theorized that the cyst lining epithelium progressed and underwent ameloblastomatous change. Histopathologically this is a feasible concept because the epithelial cell rests of Malassez, which gives rise to radicular cyst, have been implicated in the origin of multiple odontogenic cysts and neoplasms . In addition, the histopathological examination results are consistent with the above consideration. Furthermore, we observed small follicular ameloblastoma islands in the cyst wall connective tissues. The final histopathological diagnosis was follicular ameloblastoma. Another plausible explanation is that these entities may represent a collision phenomenon. The occurrence of collision lesions, including those of an odontogenic epithelial nature, is not uncommon in the jawbones [9–13]. That only radicular cysts were enucleated and diagnosed in 2006 may be due to the fact the ameloblastoma developing in the same area was in its incipient stage and therefore undetected.
In summary, this case reported here may represent an example of radicular cyst and ameloblastoma occurring as a collision phenomenon, or of an amelo blastoma arising from a result of neoplastic transformation of the lining epithelium in an inflammatory odontogenic (radicular) cyst. Although, their true relationships remain unknown, nonetheless the considered pathogenesis was consistent with the course of histopathology and radiography.