Posted: March 31, 2014, 4 a.m. EDT
© Courtesy Leticia Materi, PhD, DVM
An infection of the middle ear can spread to the facial nerve and affect facial muscles.
Even though they make a rabbit so unique, the ears are not something that many rabbit owners spend much time paying attention to (unless it comes to kissing them!). Most of the time, the ears cause few problems for rabbits, but on occasion they can develop disease that needs to be addressed by owners. To understand the disease, it helps to understand the anatomy of the rabbit ear.
Like other mammals, the rabbit ear is comprised of three parts:
1. The outer ear consists of the pinna (the kissable part that sticks out from the head) and the ear canal that leads from the base of the pinna to the eardrum. The pinnae make up about 12 percent of the rabbit’s body surface. In addition to gathering sound waves, the pinnae help regulate body temperature. When a rabbit becomes too warm, the blood vessels in the ears dilate and the ears are held away from the body to allow excess heat to escape.
2. The middle ear is housed within the temporal bone of the skull. It is an air-filled space that houses small bones that transmit sound waves from the eardrum to the internal ear, the facial nerve that eventually connects to the muscles of the face, and the opening of the auditory (Eustachian) tube that connects the middle ear to the throat. We have a similar tube that allows our ears to "pop” during pressure changes like when we are in an airplane.
3. The inner ear houses the organs necessary for hearing (cochlea) as well as for balance (vestibular organ).
Disease can occur in any of these areas. The following outlines various medical conditions that can occur to the rabbit ear:
1. Diseases of the outer ear: The pinnae may be damaged due to trauma or frostbite. Lop-eared rabbits are especially prone to infections and abscess development involving the ear canal. Resolution of chronic ear abscess often involves surgery. Ear mites can live within the ear canal and are very painful for rabbits.
2. Diseases of the middle ear: Infection can spread into the middle ear, often ascending up the Eustachian tube from the nose and/or throat. This can often be diagnosed by X-rays of the skull. In advanced cases, the facial nerve can be damaged, leading to loss of nerve input and subsequent degeneration of the facial muscles on the affected side, as seen in the rabbit photo. These rabbits have significant asymmetry to the face.
3. Diseases of the inner ear: Infections by bacteria or E. cuniculi, a parasite, can damage the structures of the inner ear leading to abnormal balance or hearing loss.
Routine annual health examinations can detect early signs of ear disease. If you are worried that your rabbit may have ear problems, please contact your veterinarian for an assessment. Proper treatment early in the course of the disease may improve your rabbit’s prognosis.
Note: This article is meant for educational purposes only and in no way represents any particular individual or case. It is not for diagnostic purposes. If your pet is sick, please take him or her to a veterinarian.
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