Ameloblastoma with prominent stromal ossification.

A large ameloblastoma with prominent stromal ossification is reported. The patient was a 39-year-old Japanese male with diffuse swelling of the mandible from the left molar to the right premolar region. Radiographic examination showed a radiopaque lesion suggestive of a fibro-osseous lesion. However, histologic examination revealed the lesion to be a variant of follicular ameloblastoma. Most of the tumor cells appeared to be squamous metaplasia. The stroma was abundant, with prominent formation of bone trabeculae rimmed by osteoblasts. Differentiation of mesenchymal cells into active osteoblasts with formation of new bone trabeculae was frequently found in the stroma. The prominent stromal bone formation appeared to be reactive in nature, although it remains uncertain whether this type of ameloblastoma can be regarded as a discrete clinicopathologic entity.