ADVERTISEMENT

Surgery of the ear (Proceedings)

source-image
Nov 01, 2010

Anatomy of the ear

There are three divisions of the ear:
      1. The external ear consists of the pinna and external auditory meatus. Its function is as a sound collecting system.
      2. The middle ear consists of the tympanic membrane (the eardrum), the tympanic cavity, and the stapes, incus, and malleus. It's funiction is as a sound conducting system The tympanic membrane separates the external ear from the middle ear.
      3. The inner ear consists of the semicircular canals and the cochlea. I's function is for both hearing and equilibrium.

The pinna of the external ear may vary a great deal between breeds. There are two cartilage segments that support the external ear and the ear canal. The auricular cartilage forms the pinna, the base of the ear, the horizontal and part of the vertical canal. The annular cartilage acts as the framework for the vertical canal and is attached to the external acoustic process and the auricular cartilage.

Examination of the ear

The pinna of the ear is examined for scratches, hair loss and swelling. The external ear canal that is visible to the naked eye is examined for redness, swelling, and mats of hair and waxy material. The inflammation, hematomas, and hair may indicate irritation to the ear which is the first step in the pathogenesis of otitis externa.

Otoscopic examination allows one to explore the ventral vertical canal, horizontal canal and tympanic membrane (eardrum). The examiner is then able to note any trauma, foreign bodies, hair mats, ectoparasites, etc. that may be present. The tympanic membrane should be examined for any variance from its normal concave, pearly gray color and glistening appearance.

Lesions of the ear

It is important not to forget that the ear can be an indicator of other systemic problems, for example, hypothyroidism, generalized dermatitis, eczema, etc. Therefore remain alert of other problems when diseases of the ear are seen.

Pinna

Disease of the Pinna may be associated with otitis externa. The Pinna may be inflamed in the early stage or thickened, scaly, and exudative in later stages. This results from some type of irritation in the external ear canal, otitis externa, foreign bodies, or irritation to the Pinna itself Aural hematomas in the canine and feline can result from otitis externa which causes the animal to shake its head and scratch at the ears. Separation of the skin from the cartilage on the concave side of the ear occurs and results in vessel rupture, hemorrhage, and hematoma formation when treating aural hematomas, it is imperative that the cause be sought and abolished.

Otitis externa

The factors that predispose to otitis externa are all forms of irritation to the ear, for example, foreign bodies, ear mites, allergies, dermatitis, excess moisture, infection by bacteria or fungi, hair mats and trauma. One should always attempt to determine the etiologic agent These can compound the problem of poor ear canal conformation and can often lead to secondary problems such as aural hematoma and otitis media. The animal may be presented to the veterinarian because it shakes its head constantly, continually scratching at its ears or has a head tilt if the middle ear is infected. Since the major portion of the auditory canal is vertical it makes drainage difficult. Shaking of the head removes accumulations by centrifugal force. The auditory canal provides a warm, dark, moist environment, which is ideal for microorganisms such as Staphylococcus sp., Corynebactertum Sp., Pseudomonas sp., Proteus sp., and Pityrosporum sp. yeast). Upon physical examination there may be a black or tan odiferous discharge from the ear. The ear will be full of debris, wax, hair or foreign bodies. The ear canal may be red and swollen and in the late stages ulcerated. The tympanic membrane should be visualized to determine if otitis media is present. The normal eardrum looks like a fish scale with a glistening surface. In cases of otitis media, the membrane may appear to bulge and be dull and opaque, yellow to red in color or it may have ruptured which confirms the diagnosis of otitis media.