Effect of Spatial Orientation of the Horizontal Semicircular Canal on the Vestibulo-Ocular Reflex.

OBJECTIVE: To determine if an alignment of the horizontal semi-circular canal (hSCC) with the plane of rotation would enhance the vestibular-ocular reflex (VOR) gain result as it has been previously suggested. STUDY DESIGN: Comparative study of a physiological vestibular function test in healthy subjects. SETTING: Tertiary referral center for otology and neurotology. PATIENTS: Twenty two healthy volunteers were recruited for this study. Their mean age was 25.6 years and the sex distribution was 14:8 (M:F). None of the subjects had a history of audiovestibular disorders. INTERVENTION: The video Head Impulse Test (v-HIT) was performed with the hSCC in the conventional position (head upright, horizontal gaze) and also with the hSCC in-line with the earth horizontal. MAIN OUTCOME MEASURES: depending on the alignment of the hSCC with the plane of head rotation. RESULTS: There was no significant difference between the results, either for the VOR gain at 60 ms, or the regression slope gain, when the two alternative head positions were compared. CONCLUSIONS: The data acquired in this study show that the VOR as measured by the v-HIT is not enhanced by aligning the plane of the hSCC with the plane of rotation during the testing procedure. Hence, we recommend that the positioning of the patient, with the head upright and a horizontal gaze direction should be routinely used in the clinical evaluation of the angular VOR by v-HIT.

Audiovestibular Function Deficits in Vestibular Schwannoma.

Introduction. Vestibular schwannomas (VS) are benign tumours of the vestibular nerve and can lead to hearing loss, tinnitus, vertigo, facial palsy, and brainstem compression. Audiovestibular diagnostic tests are essential for detection and treatment planning. Methods. Medline was used to perform a systematic literature review with regard to how audiovestibular test parameters correlate with symptoms, tumour size, and tumour location. Results. The auditory brainstem response can be used to diagnose retrocochlear lesions caused by VS. Since hearing loss correlates poorly with tumour size, a retrocochlear lesion is probably not the only cause for hearing loss. Also cochlear mechanisms seem to play a role. This can be revealed by abnormal otoacoustic emissions, despite normal ABR and new MRI techniques which have demonstrated endolymphatic hydrops of the inner ear. Caloric and head impulse tests show frequency specific dynamics and vestibular evoked myogenic potentials may help to identify the location of the tumour regarding the involved nerve parts. Conclusion. In order to preserve audiovestibular function in VS, it is important to stop the growth of the tumour and to avoid degenerative changes in the inner ear. A detailed neurotological workup helps to diagnose VS of all sizes and can also provide useful prognostic information.