Vestibular Disease

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Overview

The vestibular system is the primary sense that governs balance. Just like vision depends on the eyes to convert light to electrical impulses and then requires a specialized region of the forebrain to interpret the information correctly, the vestibular system also depends on two components. These are the inner ear structures that convert information about head position into electrical impulses and then an area of the brainstem that interprets this information. An animal can have a disturbance of balance due to either a problem affecting the inner ear, such as a severe and deep-seated ear infection, or the problem could be caused by either a tumor or an infection in the vestibular center of the brainstem. The signs of vestibular disease include not only a loss of balance but also a head tilt and nystagmus. Nystagmus is a specific, involuntary eye movement where the eyes flick rapidly in one direction and then slowly drift back before repeating the movement again. Diagnosis depends first on a full neurological examination to differentiate inner ear problems (usually called peripheral vestibular disease) from brainstem disorders (usually called central vestibular disease). Depending on the examination results, the structures of the ear and brainstem may need to be imaged using either a [intlink id=”1503″ type=”post”]CT scan or an MRI[/intlink]. In addition, a sample of CSF may also need to be taken. Treatment and prognosis will depend on the results of these tests.

Figure 9: A: CT scan of the skull of a cat with peripheral vestibular disease due to otitis media and interna (inflammation of the structures of the middle and inner ear). The right tympanic bulla (white arrowheads) is normal; it is full of air, which shows as black on the CT scan. The left tympanic bulla (white arrow) is full of either fluid or tissue and the bony wall is also thickened slightly compared to the right side. The inflammation within the left bulla has affected the structures of the inner ear (position indicated by the black arrowhead) to cause the typical clinical signs of vestibular disease. The position of the vertical and horizontal canals of the left external ear are shown by *.

B: CT scan of the skull of a dog with normal tympanic bullae but a tumor (arrowheads) within the brainstem. This is an example of an animal with central vestibular disease. The tumor shows up as whiter then the rest of the brain because it has enhanced after the administration of intravenous contrast.

The prognosis is generally good for peripheral vestibular disease but is more guarded for central vestibular disease. Complications are dependent on the specific diagnosis.

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