Spontaneous Ameloblastic Fibroma in a Young Guinea Pig

A spontaneous ameloblastic fibroma was found in a 9-week-old guinea pig.Histopathologically, neoplastic cells consisted of two components: an odontogenicepithelium and odontogenic mesenchyme. The odontogenic epithelium formed strands, nestsand islands that were interspersed within the odontogenic mesenchyme. In the marginalregion, odontoblasts and scant dysplastic eosinophilic material were seen between thesetwo components. Immunohistochemically, the odontogenic epithelium was positive forcytokeratin AE1/AE3, and the odontogenic mesenchyme and odontoblast were positive forvimentin, in the same manner as in the normal tooth germ (control). We could not obtainconclusive data suggesting that the eosinophilic material was dental hard tissue becausethe eosinophilic material was not stained specifically by any methods. Based on thesehistological characteristics, the tumor in the present case was diagnosed as anameloblastic fibroma. This is the first report of ameloblastic fibroma in guinea pigs.