Cytological features of malignant metastatic ameloblastoma: a case report and differential diagnosis.

In this report, the cytological features and differential diagnosis of the metastasis from and subsequent local recurrence of an unusual case of malignant (metastatic) ameloblastoma are described, with histological confirmation. Characteristic cytological findings included fibrovascular central cores surrounded by palisading crowded basaloid or columnar cells or both and rosette-like structures of tumor cells with central fibrillary material. Keratin debris in the background and cystic cavities were prominent components of the metastatic ameloblastoma. The basaloid cells showed scant-to-absent cytoplasm, round-to-oval to tear-shaped nuclei, rare longitudinal nuclear grooves, single or multiple nucleoli, and smooth-to-clefted nuclear contours. No features to predict malignant behavior were identified (abundant mitotic activity, necrosis, nuclear pleomorphism). The cytological features of ameloblastoma appear to be characteristic enough to allow definitive diagnosis. However, since the cytology of this tumor is underreported in the literature, the unwary observer could easily misdiagnose it, especially at metastatic sites.