Ear canal tumors may arise from any of the tissues lining or supporting the ear canal, including the squamous epithelium, the ceruminous or sebaceous glands, or 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 the infection and inflammation over time can change the appearance of these growths and, in some cases, they will actually disappear. In contrast, neoplastic growths will not resolve with topical otic therapy.
Although the precise cause of ear canal tumors is unknown, several theories have been postulated. Chronic inflammation of the ear canal may lead to hyperplasia, followed by dysplasia and finally neoplasia. Bacterial degradation of the fatty acids and other products produced in inspissated apocrine secretions from hyperplastic ceruminous glands during otitis externa episodes may also stimulate 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. This seems to be attributed to chronicity of ear disease rather than simply age. Tumors in the ear canal decrease the lumen diameter, which leads to impaired drainage of inflammatory exudates and volatile fatty acids. Chronic infection and inflammation do not subside, allowing neoplastic changes to continue to develop.
Incidence of benign and malignant ear tumors is higher in American Cocker Spaniels than in other breeds, likely due to chronic inflammation and ceruminous gland hyperplasia seen in otitis in this breed. Middle-aged to older cats are predisposed to benign and malignant ear canal tumors, whereas young cats (3 months to 5 years) are more likely to develop nasopharyngeal polyps.
Clinical signs of an ear canal tumor include:
Often, aural hematomas result from the head shaking associated with ear canal tumors. Draining abscesses in the parotid region below the affected ear may result. If there is middle or inner ear involvement, neurologic signs may be present, 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 any case 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, with <10% showing any lymph node involvement. Invasion of tumor into the bulla or surrounding tissue indicates a poorer prognosis. Cats have a higher incidence of malignant otic tumors.
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 are occasionally seen in the middle or inner ear of dogs and cats. (Also see Tumors of the Skin and Soft Tissues.)