Examining the Ear Canal

For examination of the cleaned, dry ear canal, it is helpful to determine whether the otitis externa is acute or chronic. Chronic otitis externa is characterized by epithelial hyperkeratosis, glandular hyperplasia, fibrosis, stricture, and inflammatory cell infil­tration of the dermis of the external auditory canal.

Pathologic changes associated with otitis externa may extend the entire length of the ear canal and may affect the tympanic membrane. One report involving histopathologic evaluation of postmortem specimens from dogs with chronic otitis demonstrated that hair and keratin originating from the external ear were often found in the middle ear. The tympanic membrane in these specimens could not be identi­fied histologically in a significant number of cases, and when it could be identified, it was often thickened.

When the eardrum is ruptured, exudates drain from the external ear canal into the tympanic bulla. The mucous membrane lining the bulla, the mucoperiosteum, becomes inflamed and can produce copious exudates, complicating the continued treatment of otitis externa. Liquid medications placed into the external ear canal cannot reach the bulla if the canal is already filled with mucus and pus.