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History

6-year-old Percheron gelding, one year history of progressive swelling along right ear. Swelling was first discovered by an equine dentist upon routine teeth floating. Radiographs by the referring DVM identified a mass next to the right ear. The mass has progressively enlarged to a non-painful ~8cm swelling ventral to the right external ear canal, with no discharge noted.

CT Images

Transverse bone window

Dorsal bone window

Sagittal bone window

  • Centered at and expanding the right petrous temporal bone is a large (8.23 cm W x 5.96 cm H x 6.65 cm L), rounded and lobulated, smoothly marginated, heterogeneously mineral attenuating mass that extends from the level of caudal temporomandibular joint to the caudal occiput. Throughout the mass are multiple rectangular, lamellated structures with layering typical of teeth that are mineral attenuating and isoattenuating to dental material.
  • Caudal to the horizontal ear canal, the mass has a large component that extends ventrolaterally with thickening and bulging of the adjacent soft tissues.
  • The mass is causing severe thinning of the adjacent calvarium including the temporal and occipital bones with intracranial bulging of the mass along the right occipital lobe. -The right horizontal ear canal and cavity of the tympanic bulla contain homogeneous soft tissue attenuating material
  1. Right temporal heterotopic polyodontia (dentigerous cyst) or temporal teratoma, with pressure necrosis of the temporal and occipital bones and suspected intracranial extension.
  2. Associated obstructive right otitis media and externa.

Temporal heterotopic polyodontia, also known as dentigerous cysts, temporal teratoma, or “ear teeth”, is a congenital anomaly that most commonly presents as a mass swelling around the base of the ear associated with the temporal bone that can be firm (bone or dental tissue) or soft and fluctuant, with or without a draining tract. They are benign structures known by many names with variable nomenclature, and may contain dental elements with enamel components, some variant of a dental alveolus, bony association with the cranium, a cystic epithelial lining, and a fibrous capsule. They often occur unilaterally, but have been reported to occur bilaterally and in other locations such as the paranasal sinuses and cranium. Most are diagnosed in young horses before 2 years of age, however they can be recognized at any age. Skull radiographs are useful for diagnosis, but may be limited by superimposition. Computed tomography can provide additional information about location, extent, and cyst contents for potential surgical planning. Positive contrast fistulogram may also be helpful for further evaluation of a draining tract, if present.

Dentigerous cysts are often disconcerting to the owner due to possible disfigurement of the head and potential for draining tract formation. Medical management is often unrewarding, and surgical removal with total resection of dental elements, cyst capsule, and epithelial lining is the treatment of choice when technically feasible. Incomplete resection can lead to recurrence of clinical signs, however surgical treatment is usually successful with minimal recurrence if complete excision is accomplished. Due to the extensive nature of disease in this case and suspected intracranial extension, surgical removal was not considered a viable option. The horse was discharged for at-home monitoring and supportive care.

References

1. Dentigerous cysts: Congenital anomaly of many names. Gaughan E. Equine Veterinary Education. 2010 Jun;279-280.

2. Bilateral dentigerous cysts (heterotopic polyodontia) in a yearling Standardbred colt. Smith L, Zedler S, Gestier S, et. al. Equine Veterinary Education. 2012 Nov;573-578.

3. What is Your Diagnosis. Ruby J, Scribani P, Thompson M. JAVMA. 2015 Nov;10:1097-1099.

4. Congenital Diseases of the Equine Head. Gaughan E, DeBowes R. Vet Clinics of North America: Equine Practice. 1993 Apr;9:101-103.