Histo-pathological study of a malignant ameloblastoma associated with prominent new bone formation of the maxilla.

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The classification for odontogenic tumors of the World Health Organization was revised 21 years after first being issued. The term "malignant ameloblastoma" has been especially controversial because there was special emphasis on metastasis without a statement on histology in the former WHO classification. According to the revised WHO classification, malignant ameloblastoma is a neoplasm in which the pattern of an ameloblastoma and cytological features of malignancy are shown by the primary growth in the jaws and/or by any metastatic growth.<BR>This paper presents an extremely rare malignant ameloblastoma of the maxilla which histologically showed malignant features together with prominent new bone formation. The patient was a 46-year-old Japanese female who visited our hospital complaining of pain in the right upper premolar region. An incision had been made in the second premolar region and the second premolar had been extracted 2 months before her initial visit. At physical examination, diffuse swelling was observed in the right cheek and maxilla alveolus; the overlying mucosa of the alveolar process and palate displayed redness. Orthopantomogram revealed a ground-glass appearance extending from the canine to the second molar, and the right antrum was pushed upward. CT X-ray revealed new bone formation in the right maxilla and just outside of the anterior wall of the maxilla. The tentative diagnosis was sclerosing osteomyelitis or fibro-osseous lesion. However, biopsy specimen examination revealed an ameloblastoma with cytological malignancy. We performed right hemimaxillectomy under general anesthesia. Histologically, most of the tumor showed the pattern of a follicular ameloblastoma which consisted of basaloid cells. Atypical cells including hyperchromatism, increased N/C ratio and mitosis were also observed. Vigorous bone formation was seen throughout tumor, but bone destruction by the tumor was also observed in some parts. New bony trabeculae were surrounded by many active osteoblasts. The nests or sheets of the tumor were observed among new bone. Partial resection of the left maxilla was performed because recurrence of the tumor was detected in the resected margin of the palate about 2 years after the first operation. The postoperative course has been uneventful after the second operation, and no recurrence or metastases have been observed for 7 years.

Histo-pathological study of a malignant ameloblastoma associated with prominent new bone formation of the maxilla.

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