What is Hearing Preservation Cochlear Implantation?

A blog for Parents, Patients & Professionals.

Traditionally, patients with profound high frequency hearing loss and residual low frequency hearing in the normal/mild/moderate hearing loss range, would not have been offered cochlear implantation (CI). This decision being influenced by concern about losing the benefit from the residual natural hearing after CI, or a perception that their residual hearing was too good or good enough to receive substantial benefit from modern conventional hearing aids.

The development of CI electrode arrays and surgical techniques (‘soft surgery’) aimed at minimising intra-cochlear trauma following array insertion, has been one of the most significant advances in the field of CI. Ultimately, the aim of hearing preservation (HP) CI being that patients can hear high frequency sounds ‘electrically’ and low frequency sounds either ‘naturally’ or with the aid of ‘acoustic stimulation’. In some medical texts this is referred to as ‘electroacoustic stimulation’ (EAS). The potential benefits of EAS include improved listening in background noise (real life listening) and greater appreciation of music and the meaning of intonation.

The factors influencing successful HP remain under investigation, but several factors are thought to be important: electrode design (dimensions and stiffness), atraumatic insertion, steroid use, age and as yet unknown patient factors. Certainly, it is possible to perform uneventful ‘textbook’ surgery with resultant wide variability in preservation of natural hearing.

As such, patients should be counselled about the chance of success (varies between 50 – 90+%). The strengthening evidence detailing successful hearing preservation using ‘standard’ length electrode arrays is such that I now avoid using the generation of ‘bespoke’ short HP electrode arrays. These short electrode arrays may have slightly higher hearing preservation rates, but the patient may be worse off if the residual hearing is lost at surgery or in the years that follow. I believe that it is better to have electrodes switched off and sequentially activated to match hearing deterioration over time, than to be faced with a second surgery to insert a standard length electrode array, or accept a sub-optimal long-term outcome.

The introduction of bilateral simultaneous CI (predominantly children and young people in the UK) provoked some anxiety about the effect on balance function, with the potential generation of significant numbers of chronically imbalanced patients. Thankfully, this does not appear to be the case. The adoption into standard practice of the ‘soft surgery’ techniques originally developed for HP cases may further reduce the risk to the balance organ in the inner ear, whilst aiding the future replacement of failed or outdated CIs by limiting intra-cochlear inflammation and scarring (fibrosis).

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Aspects of this blog were based on the chapter I have written with Ingo Todt (Berlin) on Hearing Preservation Cochlear Implant Surgery.

Published shortly in Advances in Hearing Rehabilitation. Karger Publishers (2018). ISBN: 978-3-318-06314-1