Overview of Tumors of the Ear in Small Animals

Ear canal tumors can arise from any tissues lining or supporting the ear canal, including the squamous epithelium, the ceruminous or sebaceous glands, and the mesenchymal tissues. Malignant tumors arising from the external ear canal and pinna are more common in cats than in dogs.

True neoplasia in the ear is often misdiagnosed during physical examination, because hyperplastic epithelial tissue and glands (ceruminous gland hyperplasia) can appear as growths along the canal. Treatment of infection and inflammation over time can change the appearance of these growths, and in some cases they actually disappear. In contrast, neoplastic growths do not resolve with topical otic treatment.

Although the precise cause of ear canal tumors is unknown, several theories have been postulated. Chronic inflammation of the ear canal can lead to hyperplasia, followed by dysplasia and finally neoplasia. Bacterial degradation of fatty acids and other products in inspissated apocrine secretions from hyperplastic ceruminous glands during otitis externa episodes can also lead to carcinogenesis in the ear canal.

Middle-aged dogs and cats are more likely to have benign otic tumors, whereas dogs and cats > 11 years old seem to have more malignant tumors. The higher incidence of malignancy in older dogs and cats appears attributable to the chronicity of ear disease rather than simply age.

Tumors in the ear canal decrease the lumen diameter, leading to impaired drainage of inflammatory exudates and volatile fatty acids. Because chronic infection and inflammation do not subside, neoplastic changes continue to develop.

The incidence of benign and malignant ear tumors is greater in American Cocker Spaniels than in other dog breeds, likely because of the chronic inflammation and ceruminous gland hyperplasia that accompanies otitis in this breed.

Middle-aged and older cats are predisposed to both benign and malignant ear canal tumors. Young cats (3 months to 5 years old) are more likely to develop nasopharyngeal polyps.

Clinical signs of an ear canal tumor include the following:

• unilateral chronic otic discharge (ceruminous, purulent, mucoid, or hemorrhagic) and necrotic odor

• head shaking

• ear scratching

Auricular hematomas often result from the head shaking associated with ear canal tumors. Another sequela from ear canal tumors is a draining abscess in the parotid region, below the affected ear, that results from complete occlusion of the ear canal and a buildup of fluid and debris medial to the tumor, leading to rupture of the ear canal, with drainage ventrally.

Middle or inner ear involvement in ear canal tumors can be accompanied by neurological signs including deafness, vestibular signs (eg, head tilt, ataxia, nystagmus), facial nerve palsy or paralysis (facial drooping, salivation, and dropping food from the lips), Horner syndrome (eyelid droop, pinpoint pupil, and inward rolling of the globe), and occasional protrusion of the third eyelid.

In cases of medically refractory unilateral otitis, a neoplasm of the ear canal or middle ear should be suspected.

Ear canal tumors in dogs are more likely to be benign than malignant. Malignant otic neoplasms are locally invasive; < 10% show any lymph node involvement. Invasion by a tumor into the bulla or surrounding tissue downgrades the prognosis.

The incidence of malignant otic tumors is greater in cats than in dogs.Common ear tumors in dogs and cats are listed according to location in the table Common Ear Tumors in Dogs and Cats.

Other tumors reported in the external ear canal of dogs include inflammatory polyps, papillomas, sebaceous gland adenomas, histiocytomas, plasmacytomas, melanomas, fibromas, squamous cell carcinomas, and hemangiosarcomas. Lymphoma, fibrosarcoma, and squamous cell carcinomas occur occasionally in the middle or inner ear of dogs and cats. (Also see Tumors of the Skin and Soft Tissues.)