Computing Endolymph Hydrodynamics During Head Impulse Test on Normal and Hydropic Vestibular Labyrinth Models

In 1988, we introduced impulsive testing of semicircular canal (SCC) function measured with scleral search coils and showed that it could accurately and reliably detect impaired function even of a single lateral canal. Later we showed that it was also possible to test individual vertical canal function in peripheral and also in central vestibular disorders and proposed a physiological mechanism for why this might be so. For the next 20 years, between 1988 and 2008, impulsive testing of individual SCC function could only be accurately done by a few aficionados with the time and money to support scleral search-coil systems—an expensive, complicated and cumbersome, semi-invasive technique that never made the transition from the research lab to the dizzy clinic. Then, in 2009 and 2013, we introduced a video method of testing function of each of the six canals individually. Since 2009, the method has been taken up by most dizzy clinics around the world, with now close to 100 refereed articles in PubMed. In many dizzy clinics around the world, video Head Impulse Testing has supplanted caloric testing as the initial and in some cases the final test of choice in patients with suspected vestibular disorders. Here, we consider seven current, interesting, and controversial aspects of video Head Impulse Testing: (1) introduction to the test; (2) the progress from the head impulse protocol (HIMPs) to the new variant—suppression head impulse protocol (SHIMPs); (3) the physiological basis for head impulse testing; (4) practical aspects and potential pitfalls of video head impulse testing; (5) problems of vestibulo-ocular reflex gain calculations; (6) head impulse testing in central vestibular disorders; and (7) to stay right up-to-date—new clinical disease patterns emerging from video head impulse testing. With thanks and appreciation we dedicate this article to our friend, colleague, and mentor, Dr Bernard Cohen of Mount Sinai Medical School, New York, who since his first article 55 years ago on compensatory eye movements induced by vertical SCC stimulation has become one of the giants of the vestibular world. Show more

It is suggested that the different results of rotational (video head impulse - vHIT) and caloric tests in patients with Ménière's disease (MD) may be a consequence of the physical enlargement of the membranous duct in the hydropic labyrinths in MD, causing a reduced response to caloric stimulation.

The localization, frequency, and severity of endolymphatic hydrops in 22 temporal bones of 16 individuals with Meniere's disease were studied histopathologically. Endolymphatic hydrops was more often observed in the pars inferior (22/22) than in the pars superior (13/22) of the temporal bone, and severe hydrops was observed most frequently in the saccule, followed by the cochlea, the utricle, and the three semicircular canals. In the cochlea, the most severe hydrops was observed in the apical turn, followed by the hook portion, the middle turn, and the basal turn. Clinically interesting observations regarding endolymphatic hydrops included bulging into the perilymphatic space of the vestibule. In 17 of 22 bones the saccular membrane bulged into the vestibule laterally and was attached to the footplate of the stapes. In two of 22 bones, Reissner's membrane in the hook portion of the basal turn of the cochlea bulged superiorly into the vestibule, occupying most of the perilymphatic space of the vestibule. Show more