Vestibular schwannomas (VS) are a type of tumour which arises from Schwann cells in the vestibulocochlear nerve. Common symptoms in VS patients include hearing loss, tinnitus and vestibular function alterations. One hypothesis for these vestibular functional losses is that tumour secretions may damage the vestibular epithelia. Although benign, these tumours pose a danger to eloquent brainstem structures and excision through a trans-labyrinthine approach may be necessary. This presents an opportunity to examine the histologic state of VS patients' vestibular epithelia and relate it to their vestibular function pre-surgery. In our study, VS patients were assessed for vestibular function after informed consent using the video-assisted head impulse test (vHIT) and the cervical and ocular vestibular evoked myogenic potentials (cVEMPs and oVEMPs) before surgery. Patients were classified into 4 groups according to tumour growth and vestibular function. Vestibular epithelia were collected during the surgical intervention and fixed overnight with medical-grade formalin. The tissues were immunostained for specific molecular markers: Myosin VII (MYO7) for all hair cells (HC), Contactin-associated Protein 1 (CASPR1) for calyx afferents on type I HC and calretinin for both type II HC and calyx-only afferents. Cell counts were obtained manually. Additionally, some samples were processed for observation by Transmission Electron Microscopy (TEM). Initial data suggests a relationship between a reduced expression of CASPR1 in calyx-only afferents of the striola region and poor vestibular function regardless of tumour growth, suggesting that calyx junction dismantlement is involved in early loss of function. Acknowledgements: PID2021-1246780B-100/ AEI/10.13039/501100011033/ FEDER, UE and 202007-30-31 (Marató TV3).