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May 2014

Calf: Mandible: ameloblastic fibroma

ameloblastic fibroma

Animal: cow, 3 weeks, female

Diagnosis: Mandible: ameloblastic fibroma

Description: The mandible was locally expanded by a pink mass of 6.3 x 3.2 x 2.1 cm. It originated from the gingival region rostral to the incisors, incorporated and dislocated the first left incisor and impeded complete closing of the lips. The mass was covered by a large superficial proliferation of granulation tissue with severe, multifocal to coalescing ulceration and necrosis and prevented the calf from completely closing its lips.

Comment: The calf was clinically presented with a growing mandibular mass and euthanized with poor prognosis.

Ameloblastic fibromas are rare tumors that typically occur in young animals, most commonly in cattle. Despite its name the tissue of origin is believed to be the odontogenic epithelium and thus a part of the enamel organ. However, it induces excessive secondary proliferation of primitive mesenchyme, in case of ameloblastic fibromas without formation of dental hard tissue.

The World Health Organisation’s histological classification of tumors of domestic animals lists eight tumors that primarily derive from the odontogenic epithelium. Among these the ameloblastic fibroma is characterized by the histologic predominance of the mentioned primitive mesenchyme in which the characteristic odontogenic epithelium is intermixed. Histological classification might be partially academic though, as the World Health Organisation lists all eight tumors as locally destructive without known metastatic potential and recommends removal.

Finally, few chords of odontoblastic epithelium can also be present in peripheral odontogenic fibromas (fibromatous epulis), benign lesions that are the most common gingival tumors especially dogs.

Image and authored by Moritz Radbruch, Department of Veterinary Pathology, Freie Universität Berlin, Germany