Answer
Vestibular autorotation testing
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Because rotational chair testing requires expensive and cumbersome equipment, the vestibular autorotation test (VAT) has been developed to allow evaluation of the VOR. Also, commercially available rotational chairs allow testing at only modest head frequencies, typically less than 1 Hz, whereas VAT allows evaluation of the VOR at higher and more physiologically significant frequencies. The most commonly used system for VAT testing is from Western Systems Research, Inc. (Pasadena, CA).
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The test is performed by using a computer-generated metronome to which the patient moves his or her head for an 18-second trial period at frequencies from 2-6 Hz. Because high head frequencies are tested, smooth pursuit contributes little to the response, and the test can be conducted in a lighted room while the patient fixates on a stationary target. This test can evaluate both the vertical and horizontal VOR.
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The best use of the test may be in monitoring the VOR in patients who receive vestibulotoxic agents. The portability of the equipment allows bedside testing of hospitalized patients. The test/retest reliability of the test has been debated in the literature; therefore, it has not been adopted universally as a standard test of VOR function.
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MRI of a 26-year-old woman with progressive disequilibrium and bidirectional horizontal nystagmus shows the periventricular areas of demyelination that are characteristic of multiple sclerosis.
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MRI of a 56-year-old woman with right cerebellar ischemia. Her history included brief episodes of vertigo and a sensation of turning to the right. Her initial MRI was negative. The brief episodes were followed by prolonged episodes of vertigo, nausea and vomiting, and truncal ataxia, which prompted a second MRI study.
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MRI of a 48-year-old woman with progressive unsteadiness, projectile vomiting, and headache. She was referred for an evaluation of vertigo. Pathology proved the posterior fossa mass to be a medulloblastoma.
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MRI of a 26-year-old woman with unsteadiness and vertical nystagmus. Arrow points to an Arnold-Chiari malformation.
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Anatomy of the labyrinth.