Heterotopic Polyodontia: Diagnosis and Surgical Removal of a Dentigerous Cyst Comprising 2 Dental Structures in a 14-Year-Old Horse.

A 14-year-old American Paint Horse mare was referred for further evaluation of a firm mass with an associated draining tract at the base of the left ear suspected to be a dentigerous cyst. Approximately three months prior, the draining tract had been excised under the presumed diagnosis of an abscess with no improvement. Physical examination revealed a firm mass palpable at the base of the left ear with a draining tract that did not elicit any pain response on palpation. Digital radiographs revealed a 6x11cm mineral mass in the left temporal region. Medially, there were two projections that extended into the left temporal bone. Cone beam computed tomography (CT) showed mild thinning of the temporal bone separating the mass and the brain at the conical extension of the caudal aspect of the mass. Both structures were isolated and elevated using a combination of osteotomes, mallet, and bone rongeurs under general inhalant anesthesia with radiographs to determine complete removal. Although histopathology was declined, gross examination of both structures resembled adult molar teeth. At eight months postoperative, the owners reported that the surgical site was healed and no discharge was present. Dentigerous cysts should remain a differential for a mass with an associated draining tract at the base of the ear in horses. Practitioners should strongly consider CT when feasible for additional diagnostics in similar cases. Although benign and removal poses risk, dentigerous cysts can be surgically excised with a positive outcome.