Ameloblastoma of the mandible metastasizing to the orbit with malignant transformation. A histopathological and immunohistochemical study.

We report here a case of ameloblastoma of the mandible with multiple local recurrences and metastasis to the orbit. The patient was a 63-year-old Japanese woman with visual disturbance of her right eye. Diagnostic imaging revealed a mass occupying the right orbital apex with partial intracranial involvement. She had been surgically treated for mandibular ameloblastoma 27 years previously, and the tumour had recurred three times in the past 5 years. The orbital tumour and recurrent ameloblastomas were investigated histopathologically and immunohistochemically. The tumour changed in morphology as it recurred, from follicular ameloblastoma without atypia to apparent malignant tumours disclosing undifferentiated or squamoid features. On immunohistochemical analysis, staining for cytokeratin was positive in the squamoid cells but not in the undifferentiated cells. Both histopathologically and immunohistochemically, the orbital tumour was almost identical to the undifferentiated recurrent tumour. The orbital tumour was distinct from the primary site or sites of recurrence of ameloblastoma, and we concluded that the mandibular ameloblastoma underwent malignant transformation with multiple recurrences and finally metastasized to the orbit.