Dentigerous cyst versus unicystic ameloblastoma--differential diagnosis in routine histology

Unicystic ameloblastomas (UAs) and dentigerous cysts (DCs) have an identical clinical and radiographic appearance. Some subtypes of UAs have a better prognosis than solid or multicystic ameloblastomas, and simple enucleation is the adequate treatment. The present study was designed to test the hypothesis that UAs with small islands of ameloblastomatous epithelium may be misdiagnosed as a DC or keratocyst if no more than two histologic sections are examined.

A total of 101 resection specimens from 22 women and 73 men (mean age: 46.5 years) were selected, all showing the clinical and radiographic features of a DC. Only cysts with a minimum diameter of 15 mm in the panoramic X-ray were considered for the present investigation. The histopathologic diagnosis had been routinely established by examining two sections. For our study, the specimens were investigated by step sections at 50 microm and by staining of 5 microm thin sections with hematoxylin and eosin (H&E) at 1 mm levels. An average of 15 slides were evaluated per case.

Microscopic examination of the step sections did not reveal ameloblastomatous epithelium in the cyst lining epithelium of the 101 cases. Thus, every primary diagnosis of a dentigerous cyst was confirmed. In four cases, additional rather large odentogenic cell nests were detected with palisading of basaloid cells, while there was a lack of other signs of ameloblastic differentiation. All lesions were completely resected, and no additional treatment was performed.

Step sectioning of larger DCs may reveal associated odontogenic cell nests in some cases but does not lead to the detection of formerly missed ameloblastic cells. Thus, unicystic ameloblastomas are not misdiagnosed if only two slides are prepared for routine diagnosis of DCs.