Clinical application of the head impulse test of semicircular canal function

Abstract Objective: To review the theory, the validity and the clinical application and the new developments of the video head impulse test (vHIT) of semicircular canal function. vHIT has now superseded the caloric test as the first-line clinical test for vestibular patients. Outcomes: This review examines the origin and rationale for vHIT: how it is carried out; pitfalls in testing; the validation of the test; the interpretation of overt and covert compensatory saccades in patients with vestibular loss; how the area VOR gain is calculated. Results: The advantages of the test are considered: it is so innocuous that it can be given to patients even during acute vertigo attacks, and given repeatedly at short intervals; it is very successful for testing young children; it tests all six semicircular canals, and, unlike the caloric test, provides measures of the absolute level of canal function and so is valuable for monitoring the effect of ototoxic antibiotics as well as identifying bilateral vestibular loss. Patients with Menière’s disease have normal canal function, although their caloric results generally indicate otherwise, with hydrops being the possible cause for that divergence. vHIT has shown the new vestibular syndrome of bilateral loss of vertical canal function and it is now being used for identifying the likely cause of vertigo of patients arriving at a hospital Emergency Room – normal semicircular canal function in such patients indicating increased probability of a stroke. The theory and application of the new, but already widely used, variant called the suppression head impulse test (SHIMPs) is explained. SHIMPs is even simpler and more intuitive than the standard vHIT test and probably even better for testing children. Conclusion: This review provides the theoretical foundations for the practical application of the clinical vHIT test which has revolutionized the clinical testing of semicircular canal function.