Malignant ameloblastoma with metastasis to the skull: report of case.

An unusual case of ameloblastoma that underwent malignant change and metastasis during recurrence is described. The primary tumor of the mandible and two independent recurrent lesions found in the base of the coronoid process and in the mandibular notch were cystic ameloblastoma of follicular type, with no histological evidence off malignancy. The second recurrence developed in the soft tissues on the medial aspect of the ascending ramus and consisted of a large solid tumor mass with poorly differentiated ameloblastoma cells, which were seen clustered in blood vessels in close apposition to tumor nests. Apparently these metastasized to the temporal bone in five months. The metastatic tumor was composed of atypical follicles packed with undifferentiated hyperchromatic cells with nuclear atypia and abundant mitoses. The histological diagnosis was malignant ameloblastoma. The cerebral lesion that developed in the skull base, possibly by direct extension of the second recurrent tumor, was also regarded as malignant because of its rapidity and aggressive growth and its high sensitivity to radiotherapy.