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Surgical aspects of vestibular implantation

Presenting Author: Neil Donnelly

Published online by Cambridge University Press:  03 June 2016

Neil Donnelly ,
James Johnston ,
James Tysome ,
Patrick Axon ,
Yu Chuen Tam ,
Richard Knight  and
Ross Deas
Neil Donnelly
Affiliation:
Cambridge University Hospitals
James Johnston
Affiliation:
Cambridge University Hospitals
James Tysome
Affiliation:
Cambridge University Hospitals
Patrick Axon
Affiliation:
Cambridge University Hospitals
Yu Chuen Tam
Affiliation:
Cambridge University Hospitals
Richard Knight
Affiliation:
Cambridge University Hospitals
Ross Deas
Affiliation:
Med-El
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Abstract

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Learning Objectives: Implantable vestibular prostheses are currently being developed in order to restore balance to patients with severe bilateral vestibular hypofunction. This presentation will examine the key research findings to date and examine on going challenges.

Implantable vestibular prostheses are being developed with a view to restoring balance to patients with severe bilateral vestibular impairment that are not responsive to currently available treatments. Electrical stimulation of nerve fibres in the vestibular system in animal and human experiments has been shown to evoke eye movements which mimic the vestibular ocular reflex (VOR).

An important technical issue faced in implanting a vestibular prosthesis is ensuring optimal positioning to provide electrical stimulation to the nerve fibres. The ideal test of this would be performed intra-operatively at the time of implantation to allow precise placement, and adjustment if required.

The aims of this clinical trial were to systematically record both the ECAPs and electrically evoked eye movements obtained by electrical stimulation of the semicircular canals in patients under a general anaesthetic for translabyrinthine resection of vestibular schwannoma. This was to ascertain whether the ECAPs and eye movements are reproducible, reliable and correlated, and to allow characterisation of the ECAPs. A new implant array and surgical approach to vestibular implantation were developed. Auditory Brainstem Responses were also recorded to try and confirm preservation of hearing post. Patients were selected if they had recordable balance function and hearing in the tumour ear prior to surgery. Six patients were studied.

It was possible to demonstrate that the amplitude growth and nerve recovery functions were very similar to those observed in cochlear ECAPs but that the latency between stimulation and response was longer confirming that these are vestibular responses. Evoked eye movements under general anaesthesia were observed three out of six test cases and from more than one SCC: these eye movements are not affected by the level of anaesthesia. To date it has not been possible to demonstrate hearing preservation.