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.
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. Feline nasopharyngeal polyps, not a neoplastic growth, may be congenital or due to chronic bacterial infection in the bulla resulting from upper respiratory infections. Viruses have not been identified in polyp tissue in cats.
American Cocker Spaniels have an increased incidence of benign and malignant ear tumors compared with other breeds. The density of glandular tissue in the ear canal of this breed may be the reason. Middle-aged to older cats are predisposed to benign and malignant ear canal tumors, while young cats (3 mo to 5 yr) are more likely to develop nasopharyngeal polyps. Clinical signs of an ear canal tumor include unilateral chronic otic discharge (ceruminous, purulent, mucoid, or hemorrhagic) and necrotic odor, head shaking, and ear scratching. 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's 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. Cats have a higher incidence of malignant otic tumors. The most common pinnal neoplasms in dogs are sebaceous gland tumors, histiocytoma, and mast cell tumors. In cats, common pinnal neoplasms include squamous cell carcinoma, basal cell tumors, hemangiosarcoma, and melanocytic tumors. The most common external ear canal tumors reported in dogs are ceruminous gland adenomas and adenocarcinomas. 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. The most common external ear canal masses reported in cats are nasopharyngeal polyps, squamous cell carcinomas, and ceruminous gland adenocarcinomas. 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.)
Last full review/revision July 2011 by Louis Norman Gotthelf, DVM