Odontoameloblastoma with extensive chondroid matrix deposition in a guinea pig

Abstract

Odontoameloblastomas (previously incorporated within ameloblastic odontomas) are matrix-producing odontogenic mixed tumors and are closely related in histologic appearance to the 2 other types of matrix-producing odontogenic mixed tumors: odontomas and ameloblastic fibro-odontomas. The presence or absence of intralesional, induced non-neoplastic tissue must be accounted for in the diagnosis. Herein we describe a naturally occurring odontoameloblastoma with extensive chondroid cementum deposition in a guinea pig ( Cavia porcellus). Microscopically, the mass featured palisading neoplastic odontogenic epithelium closely apposed to ribbons and rings of a pink dental matrix (dentinoid), alongside extensive sheets and aggregates of chondroid cementum. The final diagnosis was an odontoameloblastoma given the abundance of odontogenic epithelium in association with dentinoid but a paucity of pulp ectomesenchyme. Chondroid cementum is an expected anatomical feature of cavies, and its presence within the odontoameloblastoma was interpreted as a response of the ectomesenchyme of the dental follicle to the described neoplasm. Our case illustrates the inductive capabilities of odontoameloblastomas while highlighting species-specific anatomy that has resulted in a histologic appearance unique to cavies and provides imaging and histologic data to aid diagnosis of these challenging lesions.

Keywords: Chondroid; guinea pigs; odontoameloblastoma; odontogenic mixed tumor.

Figures 1–3.

Odontoameloblastoma originating from the caudal aspect of the right maxilla with extensive chondroid cementum in a guinea pig (Cavia porcellus). Figure 1. Computed tomography still image of a transverse skull section showing an irregular, exophytic mass disrupting and effacing the orbitosphenoid bone and expanding into the right retrobulbar space (arrowheads). The mass displaced medially the last 2 maxillary cheek teeth on the right and compressed the nasopharynx, resulting in partial stenosis. Figure 2. Fragments of neoplasm primarily comprised of sheets and broad interlinking trabeculae of odontogenic epithelium (OE) with abundant sheets and aggregates of chondroid cementum (CC). H&E. Bar = 50 μm. Figure 3. The neoplastic odontogenic epithelium of the maxillary odontoameloblastoma exhibits single layers of palisading columnar-to-cuboidal epithelial cells with antibasilar nuclei (ameloblasts, A). The neoplastic odontogenic epithelium palisades along irregular ribbons of dental matrix (dentin, DE). Centrally, the epithelium has long intercellular junctions (stellate reticulum, SR) and is bordered by chondroid cementum (CC). Masson trichrome stain. Bar = 50 μm.