Ameloblastoma in a female Wistar rat.

A spontaneous ameloblastoma of the right mandible is described in a 120-week-old female Wistar rat (strain Chbb: THOM). The tumour had a locally aggressive growth pattern and was histologically characterized by sheets and islands of odontogenic epithelium bounded by a palisaded layer of ameloblast-like cells. Because of multifocal keratinizing squamous metaplasia of the stellate reticulum tissue, the tumour was classified as an acanthomatous ameloblastoma. Cyst formation, areas of stromal hyalinization and enamel matrix-like inclusions were further characteristics of the neoplasm. The epithelial elements stained strongly positive for broad spectrum cytokeratins.