Vestibular schwannoma size and vestibular function as assessed by video head impulse testing and vestibular evoked myogenic potentials

Abstract

Introduction Vestibular schwannoma (VS) is a benign tumour of the vestibular nerve. Studies investigating size versus vestibular function have measured largest axial diameter of the tumour mass and utilized a range of vestibular function tests (VFT). Understanding this relationship has the potential to enhance the clinical management of VS in patients contraindicated for MRI, and may have utility in screening/monitoring of VS. The aim of the project was to investigate the relationship between VS size and VFT. Method A retrospective review of VFTs was conducted in a tertiary referral center (2010 – 2020). VFTs included air and bone-conducted cervical and ocular vestibular evoked myogenic potentials (AC & BC cVEMPs & oVEMPs) and multiplanar video head impulse testing (vHIT). VS size was measured by region of interest volumetric calculation from axial MRI. Results One hundred and thirty-two patients were assessed. The median VS size was 0.47ml (IQR= 0.15-1.37ml). vHIT saccade metrics were the most sensitive test to detect abnormal vestibular function in VS, increasing vHIT sensitivity by 50% and vHIT detected abnormal vestibular function in 100% of patients. Increasing VS size, across patients, correlated with a higher; VEMP asymmetry ratio, horizontal semicircular canal (HSC) and posterior semicircular canal (PSC) saccade prevalence and 1st saccade amplitude, and a lower HSC and PSC gain and 1st saccade latency. Multivariate linear regression identified two metrics that explained a change in VS size: posterior canal gain (rc=-4.49 p=0.01) and BC oVEMP amplitude asymmetry ratio (rc= 1.36 p= 0.036). A significant relationship was seen between VS size and the number of test abnormalities (rc= 0.221, p<0.001). Conclusions VHIT and VEMPs are highly sensitive to detect abnormal vestibular function in VS when used in combination. Saccade metrics increase vHIT sensitivity but the potential to select patients with unilateral sensory neural hearing loss will require further research to establish the sensitivity and specificity. A difference in tumour size across patients is explained by a difference in two VFT metrics (BC oVEMP AR and PSC gain). This relationship is likely multifactorial. Larger retrospective or prospective longitudinal studies are required to establish if additional metrics explain a change in VS size.