Spontaneous Peripheral Ameloblastic Odontoma in a Male Sprague-Dawley Rat

Abstract

Peripheral ameloblastic odontoma is a rare variant of odontogenic tumor occurring in the extraosseous region. The present report describes a spontaneous tumor in male Sprague-Dawley (SD) rats. The clinically confirmed nodule in the right mandibular region was first observed when the rat was 42 weeks and remained until the terminal sacrifice date when the animal was 48 weeks of age. At necropsy, a well demarcated nodule, approximately 2.5 × 2.0 × 2.0 cm, protruded from the ventral area of the right mandible. The nodule was not attached to mandibular bone and was not continuous with the normal teeth. Histopathologically, the tumor was characterized by the simultaneous occurrence of an ameloblastomatous component and composite odontoma-like elements within the same tumor. The epithelial portion formed islands or cords resembling the follicle or plexiform pattern typical of ameloblastoma and was surrounded by mesenchymal tissue. Formation of eosinophilic and basophilic hard tissue matrix (dentin and enamel) resembling odontoma was observed in the center of the tumor. Mitotic figures were rare, and areas of cystic degeneration were present. Immunohistochemically, the epithelial component was positive for cytokeratin AE1/AE3 (CK AE1/AE3), and the mesenchymal component and odontoblast-like cells were positive for vimentin, in the same manner as in normal teeth. On the basis of these findings, the tumor was diagnosed as a peripheral ameloblastic odontoma in an extraosseous mandibular region in a SD rat. In the present study, we report the uncommon spontaneous peripheral ameloblastic odontoma in the SD rat. We also discuss here the morphological characteristics, origin, histochemical, and immunohistochemical features for the diagnosis of this tumor.

Odontoameloblastoma with extensive chondroid matrix deposition in a guinea pig

“…Our review of 2 published cases using the term ameloblastic odontoma revealed a suspected odontoameloblastoma in a llama 24 and an ameloblastic fibro-odontoma in a rat. 15 The histologic features of an ameloblastic odontoma associated with the mandibular incisor teeth of a llama described in the paper were proliferating ameloblasts in the presence of dentin. These are features suggestive of an odontoameloblastoma; however, there are no histologic images available upon which to conclusively review the diagnosis.…”

“…10,17 A consensus regarding this specific issue within the nomenclature has not been reached. The term ameloblastic odontoma is still in use, 15,24 but is described as obsolete elsewhere. 2,5 To complicate matters further, ameloblastic odontoma is frequently considered to be a synonym of odontoameloblastoma.…”

“…These are features suggestive of an odontoameloblastoma; however, there are no histologic images available upon which to conclusively review the diagnosis. 24 On assessment of the histologic images, the ameloblastic odontoma described in a Sprague–Dawley rat has an apparent abundance of ectomesenchymal stroma (pulp) relative to odontogenic epithelium, 15 therefore we would reclassify this lesion as an ameloblastic fibro-odontoma rather than an odontoameloblastoma using the classification scheme that we applied to our case. 18 However reclassification of other investigators’ published works is perilous, given that the entire specimen is typically not available for examination.…”