# Brain structural alterations in vestibular schwannoma beyond tinnitus and hearing loss

## TL;DR

This study finds brain structural changes in vestibular schwannoma patients that go beyond hearing loss and tinnitus, suggesting new non-surgical treatment possibilities.

## Contribution

The study reveals novel brain structural alterations in vestibular schwannoma patients, including increased grey matter volume and fractal dimension in frontal regions.

## Key findings

- Grey matter volume, cortical thickness, and fractal dimension are increased in key frontal regions of vestibular schwannoma patients.
- Brain changes at the paracentral lobule and precuneus correlate with tumour size, while fractal dimension at the superior frontal sulcus correlates negatively.
- Grey matter volume and cortical thickness changes are negatively correlated with hearing test results.

## Abstract

Brain tumours alter brain structures and functions. However, morphometric alterations induced by unilateral vestibular schwannoma, a benign tumour of the vestibulocochlear nerve, have not been extensively explored. Recent studies have suggested that the tumour does not grow bigger following diagnosis in several patients, suggesting an avenue for conservative therapy. This study aims to comprehensively investigate brain structural re-organizations in vestibular schwannoma patients taking into account the effects of hearing loss and tinnitus-the most common symptoms. To this end, preoperative data from 48 vestibular schwannoma pathology-confirmed patients and a healthy control group of 30 volunteers were retrospectively included in this study. The clinical and imaging data from these participants were processed. General linear models were designed to identify tumour-related brain alterations in grey matter volume and cortical thickness, alongside three other surface measures: sulcal depth, gyrification index and fractal dimension. The differences obtained were further analysed for correlation with tumour size and pure tone audiometry. Interestingly, grey matter volume, cortical thickness and for the first time, fractal dimension measures were increased in vestibular schwannoma patients across key frontal regions (PFWE < 0.05). The precuneus, superior and inferior frontal gyrus had increased grey matter volumes and cortical thickening in patients compared to controls, among other changes (P FWE < 0.05). Meanwhile, the sulcal depth and gyrification index measures demonstrated no significant alterations. Furthermore, grey matter volume changes at the paracentral lobule and precuneus were positively correlated to the tumour size, while the fractal dimension at the superior frontal sulcus was negatively correlated. Finally, grey matter volume increase at the inferior frontal gyrus and cortical thickening at the supramarginal gyrus were negatively correlated to pure tone audiometry. These findings suggest that factors beyond hearing loss and tinnitus contribute to brain structural alterations in this tumour, a better understanding of which might pave the way for non-surgical symptomatic therapies.

Adegboro et al. report increased grey matter volume, fractal dimension, and cortical thickness in key frontal regions of vestibular schwannoma patients after adjusting for age, sex, hearing loss and tinnitus. These findings contribute to a more nuanced understanding of the tumour and highlight potential targets for non-invasive management.

Graphical Abstract