The effect of pulling out cochlear implant electrodes on inner ear microstructures: a temporal bone study

[Direction of cochlear implant developments used for the correction of perimodiolar discrimination location]

Bevezetés: A cochlearis implantátum egy hallásjavító eszköz, amely elektromos impulzusokkal közvetlenül stimulálja az idegsejteket. A beültetett elektródasor ideális elhelyezése elengedhetetlen a készüléket viselők számára. Számos hazai és nemzetközi vizsgálat igazolt szignifikáns összefüggést a műtét után helyreállított elektromos hallás minőségével. Az optimális beültetés során az elektródákat a lehető legközelebb helyezzük el a ganglion spirale sejtjeihez, így az összpontosított stimuláció javíthatja a beszédértést és a beszédkészséget. Célkitűzés: Célunk az elektródasor elhelyezkedésének vizsgálata és a cochlea középtengelyéhez mért legkisebb távolságának optimalizálása, mindemellett a kedvezőbb pozíció virtuális elemzése és a behelyezett elektródák alakjának digitalizált újratervezése. Módszer: Kutatásunkhoz 10 perimodiolaris beültetett elektródasor pozicionálási eredményét dolgoztuk fel. Az intraoperatív képalkotó eljárások eredményeit elektrofiziológiás módszerekkel (impedancia, idegiválasz-telemetriai vizsgálat) vetettük össze. Eredmények: Méréseink alapján virtuálisan megalkotott elektródasorokat vetettünk össze, amelyek különböző szögben deformált (0°, 15°, 30°, 45°) bazális szakasszal rendelkeznek. Az elektrofiziológiás és a képalkotó technikák megerősítik, hogy az elektródasor kedvezőbb helyzetbe kerül, amennyiben az közelebb tud helyezkedni a cochlea középtengelyéhez. Következtetés: Az újraformált elektródasorok pozicionálása drasztikus hatással lehet a későbbi beszédértésre, a beszéd minőségére és a készülék energiafogyasztására. Orv Hetil. 2024; 165(37): 1452–1460.

Temporal bone histopathology in revision cochlear implantation

An increasing number of young infants, as early as six months of age with congenital hearing loss receive cochlear implantation, and it is probable that many of these patients will require revision surgery later in life. The possibility of explantation of the cochlear electrode and reimplantation may cause damage to the cochlea, compromising the speech perception outcome in revision implant is of concern. There is only one prior temporal bone histopathology study to look at the outcome of revision surgery and no prior study evaluating revision cochlear implantation that used the round window approach. We conducted a histopathological study of four temporal bone specimens from four patients who underwent revision cochlear implantation and when available post-operative speech perception tests were evaluated. In all cases, the reimplanted electrode followed into the same fibrous sheath without evidence of additional intracochlear damage due to revision surgery. The intracochlear damage from the initial cochlear implantation appears to be a more important factor in outcomes rather than changes associated with explantation and reimplantation.

Cochlear implant explantation: An in vitro model to evaluate electrode explant force and trauma

OBJECTIVES

Removal of a cochlear implant and its intracochlear electrode array is sometimes necessary, potentially causing cochlear explant trauma. Explantation typically occurs years post-implantation by which time reactive tissue has formed around the electrode. We aimed to create an in-vitro electrode explant model to examine explant forces and intracochlear trauma across multiple electrode types and insertion depths.

STUDY DESIGN

An in-vitro model using gel to represent tissue surrounding the electrode was developed. Pre-curved electrodes and straight electrodes at different insertion depths (20mm, 25mm, 28mm) were explanted from the model. During explantation, explant force was measured, and high-definition videos were recorded to capture electrode exit path and gel disruption.

RESULTS

Explant force patterns varied based on electrode position in the scala tympani. Explant forces did not correlate with gel disruption, which represented explant trauma. The least gel disruption occurred with pre-curved electrodes and the under-inserted straight electrode. The greatest disruption occurred with the overly inserted straight electrode.

CONCLUSION

An in-vitro model using gel to mimic tissue surrounding the electrode may provide insights into potential electrode explant trauma. Explant force did not correlate with explant trauma in our model. Pre-curved electrodes and shallower insertion depth of a straight electrode resulted in the least amount of explant trauma.

Effects of in vivo repositioning of slim modiolar electrodes on electrical thresholds and speech perception

The slim modiolar electrode has been reported to ensure better modiolar proximity than previous conventional perimodiolar electrodes and consistently high scala tympani localization. Nonetheless, variability in modiolar proximity exists even among slim modiolar electrodes, still leaving room for further improvement of modiolar proximity, which may positively affect functional outcomes. Given this, the pull-back maneuver was reported to increase the modiolar proximity of slim modiolar electrodes in a cadaveric study, but in vivo repositioning effects remain to be established. Here we identified that the pull-back maneuver led to better modiolar proximity than conventional insertion while maintaining a similar angular insertion depth. Notably, the reduced electrode-modiolus distance from the pull-back maneuver was associated with significantly lower impedances across electrodes postoperatively as well as reduced intraoperative electrophysiological thresholds than conventional insertion. Among adult cochlear implant recipients, this maneuver resulted in significantly better sentence recognition scores at three months postoperatively when compared to those with a conventional insertion; however, this benefit was not observed at later intervals. Collectively, slim modiolar electrodes with the pull-back maneuver further enhance the modiolar proximity, possibly leading to better open-set sentence recognition, at least in the early postoperative stage.

The Pull-Back Technique for the 532 Slim Modiolar Electrode

Introduction

The distance between the modiolus and the electrode array is one factor that has become the focus of many discussions and studies. Positioning the electrode array closer to the spiral ganglion with the goal of reducing the current spread has been shown to improve hearing outcomes. The perimodiolar electrode arrays can be complemented with a surgical manoeuvre called the pull-back technique. This study focuses its attention on the recently developed 532 slim modiolar electrode.

Objective

To investigate the intracochlear movements and pull-back technique for the 532 slim modiolar electrode.

Material and Methods

A decapping procedure of the cochlea was performed on 5 temporal bones. The electrode array was inserted, and the intracochlear movements were microscopically examined and digitally captured. Three situations were analysed: the initial insertion, the overinsertion, and the pull-back position. The position of the three white markers of the electrode array in relation to the round window (RW) was evaluated while performing these three actions.

Results

The initial insertion achieved an acceptable perimodiolar position of the electrode array, but a gap was still observed between the mid-portion of the array and the modiolus (the first white marker was seen in the RW). When we inserted the electrode more deeply, the mid-portion of the array was pushed away from the modiolus (the second and third white markers were seen in the RW). After applying the pull-back technique, the gap observed during the initial insertion disappeared, resulting in an optimal perimodiolar position (the first white marker was once again visible in the RW).

Conclusion

This temporal bone study demonstrated that when applying the pull-back technique for the 532 slim modiolar electrode, a closer proximity to the modiolus was achieved when the first white marker of the electrode array was visible in the round window.

Why Pre-Curved Modiolar Hugging Electrodes Only Cover The Basal Turn of The Cochlea and Not Beyond that?

The question of why pre-curved modiolar hugging (MH) electrodes only cover the basal turn of the cochlea and not beyond that is unanswered yet in the CI field. Therefore the aim of this article is to show what the practical limitations are with the pre-curved MH electrode design in not being able to fabricate beyond one full turn. Every CI electrode design needs a metal mold with grooves for placing the platinum wires and for injecting with the silicone elastomer. Limitations in making a mold with groove that goes beyond one full turn of curvature along with the mechanical deformation of the curved silicone elastomer, prevents making a pre-curved MH electrode beyond one full turn. Electrode tip fold-over, electrode scalar deviation and the inconsistent electrode to modiolus wall proximity are the reported issues with this electrode type which does not help by any means to the operating surgeon and the pediatric candidates especially. If intra-operative imaging is recommended to confirm the proper placement of the electrode for one particular electrode design, then how many clinics in the world may have this facility and is it ethical to put the patient under more radiation risk are the natural questions that needs to be answered in the interest of the patient. Every CI brand should come out of their marketing philosophy and innovate what is essential in bringing the full benefit of the device to the patients.

Advances to electrode pullback in cochlear implant surgery

Objective. To observe the intracochlear behavior of a cochlear implant electrode insertion technique (called “pullback”) in temporal bones. Study Design. Experimental. Settings. Tertiary referral center. Method. The change of the intracochlear electrode position was investigated under various conditions of an electrode pullback (N = 54) in 9 radiologically, size-estimated temporal bones (TBs). Those TBs were prepared by removal of the cochlear scalar roof to apply digital video capture procedures to monitor the pullback procedures. The digitally captured pictures were analyzed with specific software. Results. An optimal pullback of the electrode varied between 1.37 mm and 2.67 mm. While a limited pullback is without risk, an extended pullback bears the risk of removing the electrode tip out of its initial position or out of the cochlea. A correlation between cochlear size and the amount of pullback was not found. Conclusion. An initial insertion to the first or the second marker on the electrode followed by a limited pullback of about 1.37 mm to 1.5 mm can be recommended to achieve an optimized perimodiolar position. A pullback of up to two marker positions bears the risk of removing the electrode tip out of its initial position.