Electrically evoked auditory brainstem responses in adults and children: effects of lateral to medial placement of the nucleus 24 contour electrode array

Curvature analysis of CI electrode arrays: a novel approach to categorize perimodiolar positions without anatomical landmarks

PURPOSE

Perimodiolar electrode arrays may be positioned regular, over-inserted or under-inserted into the cochlea depending on the cochlear size and shape. The study aimed to examine whether there are differences between these groups in the local curvature along the intracochlear array. Individual curvature variables were developed to categorize the groups and the relationship between the curvature and the angular insertion depth at the electrode tip was analyzed.

METHODS

The curvature along the intracochlear array was measured in the CBCT image of 85 perimodiolar electrodes of a single type. The mean curvature and the ratio of the mean curvature at contacts E14-16 to the mean curvature at E7-8 (bowing ratio) were calculated across the array, and its true positive rate (TPR) and false positive rate (FPR) were calculated to establish optimal threshold values to categorize the groups.

RESULTS

68.2% of the cases were categorized as regular positioned, 22.4% had an over-insertion and 9.4% had an under-insertion. The mean curvature was significantly weaker with under-insertion (< 342°) than with normal insertion depth (≥ 342°). With an over-insertion, the bowing ratio was < 1 and otherwise > 1. Both the mean curvature and bowing ratio were found to have an optimal threshold value with high TPR (= 1.00) and low FPR (≤ 0.06) for categorizing under-insertion and over-insertion, respectively.

CONCLUSION

Curvature analysis is a useful tool to assess if a perimodiolar electrode array has been inserted deep enough into the cochlea. Independent of critical anatomical landmarks, over-inserted arrays and under-inserted arrays could be well categorized by using individual curvature variables. The results need to be validated using additional data sets.

[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.

Predicting Cochlear Implant Electrode Placement Using Monopolar, Three-Point and Four-Point Impedance Measurements

OBJECTIVE

This study aimed to investigate the relationship between cochlear implant (CI) electrode distances to the cochleas inner wall (the modiolus) and electrical impedance measurements made at the CIs electrode contacts. We introduced a protocol for three-point impedances in which we recorded bipolar impedances in response to monopolar stimulation at a neighboring electrode. We aimed to assess the usability of three-point impedances and two existing CI impedance measurement methods (monopolar and four-point impedances) for predicting electrode positioning during CI insertion.

METHODS

Impedances were recorded during stepwise CI electrode array insertions in cadaveric human temporal bones. The positioning of the electrodes with respect to the modiolus was assessed at each step using cone beam computed tomography. Linear mixed regression analysis was performed to assess the relationship between the impedances and electrode-modiolar distances. The experimental results were compared to clinical impedance data and to an existing lumped-element model of an implanted CI.

RESULTS

Three-point and four-point impedances strongly correlated with electrode-modiolar distance. In contrast, monopolar impedances were only minimally affected by changes in electrode positioning with respect to the modiolus. An overall model specificity of 62% was achieved when incorporating all impedance parameters. This specificity could be increased beyond 73% when prior expectations of electrode positioning were incorporated in the model.

CONCLUSION

Three-point and four-point impedances are promising measures to predict electrode-modiolar distance in real-time during CI insertion.

SIGNIFICANCE

This work shows how electrical impedance measurements can be used to predict the CIs electrode positioning in a biologically realistic model.

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.

Comparison of Perimodiolar Electrodes: Imaging and Electrophysiological Outcomes

BACKGROUND

The perimodiolar CI532 Slim Modiolar electrode has been designed to bring the electrode contacts close to auditory nerve while reducing cochlear trauma during its insertion. It is currently unknown to what extent the electrode position and electrophysiological outcomes of the Slim Modiolar electrode differ from other perimodiolar electrodes.

OBJECTIVES

The objective was to compare the electrode position and electrophysiological outcomes between the CI532 Slim Modiolar and CI512 Contour Advance electrode.

METHOD

Forty-six adult patients received a Slim Modiolar or Contour Advance electrode. Electrode types were compared using intraoperative electrode impedances, evoked compound action potential (ECAP) and stapedius reflex thresholds, as well as position parameters from postoperative computed tomography or digital volume tomography images (medial-lateral position, electrode-to-modiolus distance, insertion angle).

RESULTS

The medial-lateral position indicates a closer modiolar placement of the Slim Modiolar compared with the Contour Advance. Individual electrode contact measurements, however, showed significantly larger electrode-to-modiolus distances and higher ECAP thresholds for the Slim Modiolar in the basal region. On contacts E20-22 the Slim Modiolar is slightly closer to the modiolus compared with the Contour Advance, but this did not result in lower ECAP thresholds.

CONCLUSIONS

Perimodiolar electrodes can vary in their intracochlear position, leading to divergent electrophysiological outcomes. To detect these differences, investigations must be done for each electrode contact rather than using a global factor for the whole electrode array. While the electrode dislocation rate is lower with the Slim Modiolar than with the Contour Advance, electrode-to-modiolus proximity is smaller and ECAP thresholds are lower with the Contour Advance in the basal cochlear region.

Auditory performance of post-lingually deafened adult cochlear implant recipients using electrode deactivation based on postoperative cone beam CT images

PURPOSE

The use of image processing techniques to estimate the position of intra-cochlear electrodes has enabled the creation of personalized maps to meet the individual stimulation needs of cochlear implant (CI) recipients. The aim of this study was to evaluate a novel technique of electrode deactivation based on postoperative cone beam computed tomography (CBCT) images in post-lingually deafened adult CI recipients.

METHODS

Based on postoperative CBCT images, the positioning of the electrodes was estimated in relation to the modiolus in 14 ears of 13 post-lingually deafened adult CI recipients. The electrodes sub-optimally positioned or involved in kinking and tip fold-over were deactivated. Speech perception scores in silence and in noise were obtained from subjects using the standard map and were followed up 4 weeks after image-based electrode deactivation reprogramming technique (IBEDRT). The participants selected their preferred map after 4 weeks of IBEDRT use.

RESULTS

There were statistically significant improvements in the speech recognition tests in silence and noise when comparing IBEDRT performance to the standard map. All participants elected the IBEDRT as their new preferred map.

CONCLUSIONS

IBEDRT is a promising technique for fitting CI recipients and minimizing channel interaction increased by the positioning of the electrodes sub-optimally placed, thereby improving their auditory performance. We propose a novel electrode deactivation technique based on postoperative CBCT imaging, with a limited number of deactivated electrodes and a low-dosing scanning which could be applied for clinical routine.

Examination and Comparison of Electrically Evoked Compound Action Potentials and Electrically Evoked Auditory Brainstem Response Results of Children with Cochlear Implantation without Inner Ear Anomaly

Objective

To investigate the relationship between electrically evoked compound action potentials (ECAP) and electrically evoked auditory brainstem responses (EABR) in children with cochlear implants (CI) without inner ear anomalies.

Methods

Sixteen children between the ages of two and six years who were CI users participated in the study. ECAP thresholds were recorded from one electrode in the basal, medial, and apical regions of the cochlear implant. EABRs were recorded from electrodes whose ECAP thresholds were determined. The latency-intensity functions, amplitude and morphological analyzes of the eIII and eV waves at 200 and 180 current unit (CU) excitation levels were performed. The data obtained were analyzed statistically.

Results

ECAP thresholds were found to be 171.5±11.38, 169.69±20.32 and 160.81±20.03 CU at the basal, medial and apical electrodes, respectively. EABR thresholds were also found to be 169.69±12.17, 165.62±16.41 and 160±15.49 CU in basal, medial and apical electrodes, respectively. There was a strong positive correlation between ECAP and EABR thresholds in apical, medial and basal electrodes (p<0.05). EABR threshold levels were not significantly different between basal, medial and apical region electrodes (p>0.05), and ECAP threshold values were significantly different between apical and basal region electrodes (p=0.002). When the significance values of EABR eV wave latencies were analyzed in terms of electrode region, the difference between basal and apical regions was found to be significant (p=0.03).

Conclusion

Consistency was found between ECAP and EABR recordings. However, it was concluded that one could not be preferred over the other because the data quality of the two tests was different. In future studies, ECAP and EABR recordings may be recommended by selecting more electrodes for stimulation.

Clinical investigation of the Nucleus Slim Modiolar Electrode

AIMS

The Nucleus CI532 cochlear implant incorporates a new precurved electrode array, i.e., the Slim Modiolar electrode (SME), which is designed to bring electrode contacts close to the medial wall of the cochlea while avoiding trauma due to scalar dislocation or contact with the lateral wall during insertion. The primary aim of this prospective study was to determine the final position of the electrode array in clinical cases as evaluated using flat-panel volume computed tomography.

METHODS

Forty-five adult candidates for unilateral cochlear implantation were recruited from 8 centers. Eleven surgeons attended a temporal bone workshop and received further training with a transparent plastic cochlear model just prior to the first surgery. Feedback on the surgical approach and use of the SME was collected via a questionnaire for each case. Computed tomography of the temporal bone was performed postoperatively using flat-panel digital volume tomography or cone beam systems. The primary measure was the final scalar position of the SME (completely in scala tympani or not). Secondly, medial-lateral position and insertion depth were evaluated.

RESULTS

Forty-four subjects received a CI532. The SME was located completely in scala tympani for all subjects. Pure round window (44% of the cases), extended round window (22%), and inferior and/or anterior cochleostomy (34%) approaches were successful across surgeons and cases. The SME was generally positioned close to the modiolus. Overinsertion of the array past the first marker tended to push the basal contacts towards the lateral wall and served only to increase the insertion depth of the first electrode contact without increasing the insertion depth of the most apical electrode. Complications were limited to tip fold-overs encountered in 2 subjects; both were attributed to surgical error, with both reimplanted successfully.

CONCLUSIONS

The new Nucleus CI532 cochlear implant with SME achieved the design goal of producing little or no trauma as indicated by consistent scala tympani placement. Surgeons should be carefully trained to use the new deployment method such that tip fold-overs and over insertion may be avoided.

Relationship Between Electrode-to-Modiolus Distance and Current Levels for Adults With Cochlear Implants

HYPOTHESIS

Electrode-to-modiolus distance is correlated with clinically programmed stimulation levels.

BACKGROUND

Conventional wisdom has long supposed a significant relationship between cochlear implant (CI) stimulation levels and electrode-to-modiolus distance; however, to date, no such formal investigation has been completed. Thus, the purpose of this project was to investigate the relationship between stimulation levels and electrode-to-modiolus distance. A strong correlation between the two would suggest that stimulation levels might be used to estimate electrode-to-modiolus geometry.

METHODS

Electrode-to-modiolus distance was determined via CT imaging using validated CI position analysis software in 137 implanted ears from the three manufacturers holding FDA approval in the United States. Analysis included 2,365 total electrodes, with 1,472 from precurved arrays. Distances were compared to clinically programmed C/M levels that were converted to charge units.

RESULTS

Mean modiolar distance with perimodiolar and lateral wall electrodes was 0.47 and 1.15 mm, respectively. Mean suprathreshold charge values were significantly different between each manufacturer. When combining all data, we found a moderate positive correlation (r = 0.367, p < 0.01) that was driven both by the different charge values across companies, and that the company with the highest mean charge values only offers straight electrode arrays. When grouped by electrode type, however, we found a weak correlation (r = 0.12, p < 0.01) for perimodiolar array electrodes only. When considering a single array type from any one manufacturer, only one was observed where distance mildly predicted charge.

CONCLUSION

Our results suggest that electrode distance minimally contributes to the current level required for suprathreshold stimulation.

Is electrode-modiolus distance a prognostic factor for hearing performances after cochlear implant surgery?

The aim of this study was to evaluate electrode array position in relation to cochlear anatomy and its influence on hearing performance in cochlear implantees. Twenty-two patients (25 ears) with Med-El cochlear implants were included in this retrospective study. A negative correlation was observed between electrode-modiolus distance (EMD) at the cochlear base and monosyllabic word discrimination 6 months after implantation. We found no correlation between EMD and hearing outcome at 12 months. The insertion depth/cochlear perimeter ratio appeared to negatively influence the EMD at the base. Indeed, deep insertions in small cochleae appeared to yield smaller EMD and better hearing performance. This observation supports the idea of preplanning the surgery by adapting the electrode array to the length of the available scala tympani.