Facial nerve stimulation in a post-meningitic cochlear implant user: using computational modelling as a tool to probe mechanisms and progression of complications on a case-by-case basis

Abstract

Facial nerve stimulation (FNS) is a side-effect of cochlear implantation that can result in severe discomfort for the user and essentially limits the optimal use of the implant. Three-dimensional cochlear implant modelling research has led to the progression from generic models to user-specific models with one of the intentions to develop model-based diagnostic tools. The objective of this study is to investigate the mechanisms that underlie the manifestation of FNS in the post-meningitic cochleae of a specific CI user through computational modelling. Bilateral models were created using a method previously developed for the construction of a three-dimensional user-specific volume conduction model of the cochlea and was expanded to include the facial nerve geometry. Reduced temporal bone density based on bone densitometry, cochlear duct ossification and degenerate auditory neural fibres were incorporated into a comprehensive FNS model. Auditory and facial nerve thresholds were predicted with the models showing good correspondence to perceptual thresholds and the user's FNS experience. Ossified cochlear ducts appear to aggravate the increase in thresholds caused by the otic capsule's decreased resistivity. This translational case study demonstrates the application of computational modelling as a clinical instrument in the assessment and management of complications with cochlear implantation.

Keywords:

• 3D Cochlear model
• Bone densitometry
• User-specific CI model
• Compound model

Acknowledgements

The authors wish to thank and acknowledge Dr Maurice Hockmann and Ms Wendy Deverson for support and discussions of the specific case as well as the user for agreeing to participate in the study.

Disclaimer statements

Contributors None.

Funding None.

Conflict of interest None.

Ethics approval None.

Notes on contributor

Werner Badenhorst obtained his PhD in Electronic Engineering from the University of Pretoria, South Africa, in 2018 where is presently a Lecturer in the Department of Electrical, Electronic and Computer Engineering. His research in conductance-based auditory nerve fibre (ANF) models within finite element models of user-specific models of the cochleae with cochlear implants (CIs) investigates how modelling of ANF temporal characteristics and electrically evoked compound potentials can aid in improving the performance of individual CI performance.

Tania Hanekom is a Professor in the Department of Electrical, Electronic and Computer Engineering at the University of Pretoria, South Africa. Her research is in the area of computational physiology of the electrically stimulated human auditory system. The research aims to create user-specific computer models of the auditory periphery of cochlear implant users with the objective to develop clinical tools to allow non-invasive model-based diagnostics and model-predicted customization of device parameters.

Liezl Gross obtained her M.Eng. (Bioengineering) from the University of Pretoria in 2018 on the work reported in this paper. She is currently employed in the private sector.

Johan J. Hanekom is a Professor in the Department of Electrical, Electronic and Computer Engineering at the University or Pretoria, South Africa. He is group head of Bioengineering at UP, a member of the Pretoria Cochlear Implant Unit, and has been involved with cochlear implants since 1988 when the first House/3M single-channel CIs were implanted in South Africa. His research is centred on understanding the relationship between electrical stimuli, the resulting space-time neural spike train patterns, and perception with a CI. The research involves computer modelling of processing in the central auditory nervous system and psychoacoustics.