A New Slim Modiolar Electrode Array for Cochlear Implantation: A Radiological and Histological 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.

Evaluation of a Slim Modiolar Electrode Array: A Temporal Bone Study

HYPOTHESIS

Evaluation of the Slim Modiolar (SM) electrode in temporal bones (TB) will elucidate the electrode's insertion outcomes.

BACKGROUND

The SM electrode was designed for atraumatic insertion into the scala tympani, for ideal perimodiolar positioning and with a smaller caliber to minimize interference with cochlear biological processes.

METHODS

The SM electrode was inserted into TBs via a cochleostomy. First, the axial force of insertion was measured. Next, TBs were inserted under fluoroscopy to study insertion dynamics, followed by histologic evaluation of electrode placement and cochlear trauma. A subset of TBs were inserted with the Contour Advance (CA) electrode for comparison.

RESULTS

Sixteen of 22 insertions performed to measure the axial force of insertion had flat or near zero insertion force profiles. Six insertions had increased insertion forces, which were attributed to improper sheath depth before electrode insertion. Under real-time fluoroscopy, 23 of 25 TBs had uneventful insertion and good perimodiolar placement. There was 1 scala vestibuli insertion due to suboptimal cochleostomy position and 1 tip roll over related to premature electrode deployment. When compared with the CA electrode, 14 of 15 insertions with the SM electrode resulted in a more perimodiolar electrode position. No evidence of trauma was found in histologic evaluation of the 24 TBs with scala tympani insertions.

CONCLUSION

TB evaluation revealed that the SM electrode exerts minimal insertion forces on cochlear structures, produces no histologic evidence of trauma, and reliably assumes the perimodiolar position. Nonstandard cochleostomy location, improper sheath insertion depth, or premature deployment of the electrode may lead to suboptimal outcomes.

Exploring Trauma Patterns and Contributing Factors With Slim Straight Electrode Array After Cochlear Implantation

OBJECTIVE

To assess trauma patterns associated with the insertion of lateral wall electrode arrays. The study focused on 3 categories-scala tympani (ST), intermediate, and scala vestibuli (SV)-to identify traumatic patterns and contributing factors.

STUDY DESIGN

Retrospective study.

SETTING

Data from 106 cochlear implant recipients at a tertiary otologic center.

METHODS

Demographic and surgical data were collected from recipients who underwent cochlear implantation manually and with RobOtol®. Measurements included cochlear dimensions, angular depth of insertion, and position of the first electrode. Three-dimensional reconstructions were used to analyze the electrode array location relative to the basilar membrane, categorized into ST, intermediate, and SV electrodes. Nontraumatic insertion was defined as all electrodes in the ST, while traumatic insertions had 1 or more electrodes in intermediate or SV locations.

RESULTS

Out of 106 cases, 44% had nontraumatic and 56% had traumatic insertions. Demographic and surgical characteristics showed no association with traumatic insertions. A deeper position of the first electrode, relative to the round window, was associated with traumatic insertions (P = .03). Three trauma patterns were observed: distal (facing the apical electrodes), proximal (facing the middle electrodes around 180°), and distal/proximal.

CONCLUSION

This study considers the intermediate position which could be associated with basilar membrane lesions. Risk zones for intracochlear trauma with lateral wall arrays were identified distally and proximally. Traumatic insertions were independently linked to deeper array placement. Future studies should explore whether gentler insertion, without insisting on further electrode array insertion depth, could reduce the trauma during cochlear implantation.

Identifying Slim Modiolar Electrode Tip Fold-Over With Intracochlear Electrocochleography

OBJECTIVE

To evaluate the predictive value of intracochlear electrocochleography (ECochG) for identifying tip fold-over during cochlear implantation (CI) using the slim modiolar electrode (SME) array.

STUDY DESIGN

Prospective cohort study.

SETTING

Tertiary referral center.

METHODS

From July 2022 to June 2023, 142 patients, including adults and children, underwent intracochlear ECochG monitoring during and after SME placement. Tone-bursts were presented from 250 Hz to 2 kHz at 108 to 114 dB HL. A fast Fourier transform (FFT) allowed for frequency-specific evaluation of ECochG response. ECochG patterns during insertion and postinsertion were evaluated using sensitivity and specificity analysis to predict tip fold-over. Intraoperative plain radiographs served as a reference standard.

RESULTS

Fifteen tip fold-over cases occurred (10.6%) with significant ECochG response (>2 µV). Sixty-one cases without tip fold-over occurred (43.0%) with significant ECochG response. All tip fold-overs had both a nontonotopic postinsertion sweep and nonrobust active insertion pattern. No patients with robust insertion or tonotopic sweep patterns had tip fold-over. Sensitivity of detecting tip fold-over when having both nonrobust insertion and nontonotopic sweep patterns was 100% (95% confidence inteval [CI] 78.2%-100%), specificity was 68.9% (95% CI 55.7%-80.1%), and the overall accuracy was 72.0% (95% CI 60.5%-81.7%).

CONCLUSION

Intracochlear ECochG monitoring during cochlear implantation with the SME can be a valuable tool for identifying properly positioned electrode arrays. In cases where ECochG patterns are nonrobust on insertion and nontonotopic for electrode sweeps, there may be a concern for tip fold-over, and intraoperative imaging is necessary to confirm proper insertion.

Evaluation of insertion quality of a slim perimodiolar electrode array

OBJECTIVES

The influence of cochlear morphology and electrode array design on scalar position and dislocation rates is of great interest in CI surgery. The aim of this study is to evaluate scalar position and specific points of dislocation in relation to cochlear morphology in patients implanted with a new slim perimodiolar electrode array.

MATERIALS AND METHODS

Patients were implanted using the slim modiolar electrode array (= SMA) (= 532/632 electrode array of Cochlear™). Postoperative imaging was performed via cone beam computed tomography (CBCT) and the scans were analyzed regarding cochlear morphology (distances A and B and cochlear height), scalar location of the electrode array, basal insertion depth and apical insertion angle. Furthermore, electrode array design and surgical protocols were evaluated.

RESULTS

81 ears implanted with the SMA were retrospectively included. We evaluated 3 electrode array tip fold over intraoperatively via X-ray imaging and performed revision during the same surgery. The CBCT scans showed 76 initial scala tympani (ST) insertions without dislocation. Two ears showed a dislocated array, one at 77° and the other at 163°. Three arrays were inserted into scala vestibuli (SV) via cochleostomy. These patients showed no signs of obliteration. Cochlear morphology showed no influence on angular insertion depth and scalar position.

CONCLUSIONS

The SMA showed a very low rate of scalar dislocations due to its slim electrode array design (2.7%). We could find a learning curve regarding the handling and the risk of dislocation and tip fold over with this electrode array. The rate of intraoperative tip fold over detection via X-ray imaging was 3.7%. Therefore, we highly recommend X-ray imaging and transimpedance matrix measurements within the surgery protocol. Scala vestibuli insertions happened in patients with cochleostomy only. We could identify two specific points of dislocation depending on electrode array design.

Automatic electrode scalar location assessment after cochlear implantation using a novel imaging software

As of today, image-based assessment of cochlear implant electrode array location is not part of the clinical routine. Low resolution and contrast of computer tomography (CT) imaging, as well as electrode array artefacts, prevent visibility of intracochlear structures and result in low accuracy in determining location of the electrode array. Further, trauma assessment based on clinical-CT images requires a uniform image-based trauma scaling. Goal of this study was to evaluate the accuracy of a novel imaging software to detect electrode scalar location. Six cadaveric temporal bones were implanted with Advanced Bionics SlimJ and Mid-Scala electrode arrays. Clinical-CT scans were taken pre- and postoperatively. In addition, micro-CTs were taken post-operatively for validation. The electrode scalar location rating done by the software was compared to the rating of two experienced otosurgeons and the micro-CT images. A 3-step electrode scalar location grading scale (0 = electrode in scala tympani, 1 = interaction of electrode with basilar membrane/osseous spiral lamina, 2 = translocation of electrode into scala vestibuli) was introduced for the assessment. The software showed a high sensitivity of 100% and a specificity of 98.7% for rating the electrode location. The correlation between rating methods was strong (kappa > 0.890). The software gives a fast and reliable method of evaluating electrode scalar location for cone beam CT scans. The introduced electrode location grading scale was adapted for assessing clinical CT images.

Assessment of subjective image quality, contrast to noise ratio and modulation transfer function in the middle ear using a novel full body cone beam computed tomography device

BACKGROUND

Multi slice computed tomography (MSCT) is the most common used method in middle ear imaging. However, MSCT lacks the ability to distinguish the ossicular chain microstructures in detail resulting in poorer diagnostic outcomes. Novel cone beam computed tomography (CBCT) devices' image resolution is, on the other hand, better than MSCT resolution. The aim of this study was to optimize imaging parameters of a novel full body CBCT device to obtain optimal contrast to noise ratio (CNR) with low effective dose, and to optimize its clinical usability.

METHODS

Imaging of five anonymous excised human cadaver temporal bones, the acquisition of the effective doses and the CNR measurements were performed for images acquired on using Planmed XFI® full body CBCT device (Planmed Oy, Helsinki, Finland) with a voxel size of 75 µm. All images acquired from the specimens using 10 different imaging protocols varying from their tube current exposure time product (mAs) and tube voltage (kVp) were analyzed for eight anatomical landmarks and evaluated by three evaluators.

RESULTS

With the exception of protocol with 90 kVp 100 mAs, all other protocols used are competent to image the finest structures. With a moderate effective dose (86.5 µSv), protocol with 90 kV 450 mAs was chosen the best protocol used in this study. A significant correlation between CNR and clinical image quality of the protocols was observed in linear regression model. Using the optimized imaging parameters, we were able to distinguish even the most delicate middle ear structures in 2D images and produce accurate 3D reconstructions.

CONCLUSIONS

In this ex vivo experiment, the new Planmed XFI® full body CBCT device produced excellent 2D resolution and easily created 3D reconstructions in middle ear imaging with moderate effective doses. This device would be suitable for middle ear diagnostics and for e.g., preoperative planning. Furthermore, the results of this study can be used to optimize the effective dose by selecting appropriate exposure parameters depending on the diagnostic task.

Trauma After Cochlear Implantation: The Accuracy of Micro-Computed Tomography and Cone-Beam Fusion Computed Tomography Compared With Histology in Human Temporal Bones

HYPOTHESIS

Micro-computed tomography (micro-CT) and cone-beam computed tomography (CBCT), in conjunction with the image fusion technique, may provide similar results for trauma assessment after cochlear implantation, with respect to the trauma evaluation in preclinical cochlear implant (CI) studies, as the histology.

BACKGROUND

Before clinical use, novel cochlear implant (CI) designs are tested in temporal bone (TB) studies for usability and risk evaluation. The criterion standard for evaluating intracochlear insertion trauma and electrode location has historically been with histological samples. Progress of modern imaging technology has created alternatives to classic histology. This study compares the micro-CT and CBCT fusion images between histological samples in a preclinical CI study.

METHODS

Fourteen freshly frozen TBs were inserted with a lateral wall research CI electrode. All TBs were scanned with CBCT preoperatively and postoperatively. After insertion, the TBs were prepared for micro-CT and histology. Twelve TBs underwent first a micro-CT and then the histological process. The CBCTs were used for image fusion, and all three different methods were used for intracochlear trauma evaluation. The results were compared between methods.

RESULTS

There were 4 of 14 translocations detected with the fusion image method and 3 of 12 with the micro-CT and histology. When compared, the trauma grades converged and were not statistically significant.

CONCLUSION

The trauma grading based on micro-CT is comparable to the histology. The image fusion technique based on CBCT is less accurate because it relies on an empirical assumption of the basal membrane localization, but it is clinically applicable.

Natural course of residual hearing preservation with a slim, modiolar cochlear implant electrode array

PURPOSE

Understanding residual hearing preservation and its natural course following cochlear implantation is important for developing rehabilitation strategies for hearing loss. However, non-uniform evaluation criteria and varying surgical skills pose challenges in fair comparison of the effect of different electrodes on residual hearing preservation. We compared the effect of a slim modiolar electrode (SME) and a slim straight electrode (SSE), implanted by a single surgeon, on progression of residual hearing using different parameters, based on cross-sectional and longitudinal audiological analyses.

METHODS

Patients with preoperative low-frequency pure-tone average (LFPTA) ≤85 dB at 250 and 500 Hz and who underwent minimally traumatic surgical techniques were included. The progression of residual hearing using threshold shifts, hearing preservation rate according to the HEARRING classification, and maintenance of functional low-frequency hearing potentially qualifying for a hybrid stimulation was analyzed up to five time points throughout the 1-year follow-up period.

RESULTS

Threshold shifts and hearing preservation rates according to the HEARRING classification of the electrodes were comparable from 3 months through 12 months postoperatively. Maintenance of functional low-frequency hearing, required for the usage of a hybrid stimulation, was similar for both electrodes. A substantial proportion of implantees with SME use a hybrid stimulation, resulting in long-term use. However, a difference in the pattern of postoperative residual hearing preservation between the two electrodes is possible, probably due to differences in their physical characteristics and location. Specifically, correlation analysis exhibited that significantly less tight modiolar proximity negatively affect the residual hearing preservation, albeit only at 3 months postoperatively, among patients with the SME.

CONCLUSION

Collectively, both SME and SSE implantation showed favorable residual hearing preservation. Our findings further refine the recently proposed hearing preservation with the SME and suggest that the physical characteristics and location of electrodes, in terms of electrode-to-modiolus distance, could affect loss of acoustic hearing in various ways.

Effect of initial switch-on within 24 hours of cochlear implantation using slim modiolar electrodes

Reducing electrode impedance is an important factor in improving the functional benefits of cochlear implants (CIs). The immediate effect of early switch-on within 24 h of surgery on impedance among CI recipients with various types of electrodes has been reported previously; however, the immediate change and the evolution of electrode impedances of slim modiolar electrodes after early switch-on within 24 h of implantation has not. Therefore, the focus of this retrospective cohort study of CI patients was to compare the effect of early switch-on (n = 36) and conventional switch-on (n = 72) 2–4 weeks post-operation on impedance. Compared with impedance measured intraoperatively, our results demonstrate a significant decrease in impedance from 11.5 to 8.9 kΩ (p < 0.001) at 2–4 weeks after implantation in the early switch-on group, which sharply contrasted with elevated impedance values for conventional switch-on 2–4 weeks after implantation (from 10.7 to 14.2 kΩ, p = 0.001). Notably, a comparatively lower impedance than the conventional switch-on protocol was observed for up to 2 months post-operation. Most importantly, a much earlier stabilization of impedance can be achieved with the early switch-on protocol coupled with the slim modiolar electrode array compared to the conventional switch-on protocol, offering the advantage of reducing the number of required mapping sessions in the early stages of rehabilitation.

Speech Recognition Outcomes in Adults With Slim Straight and Slim Modiolar Cochlear Implant Electrode Arrays

OBJECTIVE

To compare differences in audiologic outcomes between slim modiolar electrode (SME) CI532 and slim lateral wall electrode (SLW) CI522 cochlear implant recipients.

STUDY DESIGN

Retrospective cohort study.

SETTING

Tertiary academic hospital.

METHODS

Comparison of postoperative AzBio sentence scores in quiet (percentage correct) in adult cochlear implant recipients with SME or SLW matched for preoperative AzBio sentence scores in quiet and aided and unaided pure tone average.

RESULTS

Patients with SLW (n = 52) and patients with SME (n = 37) had a similar mean (SD) age (62.0 [18.2] vs 62.6 [14.6] years, respectively), mean preoperative aided pure tone average (55.9 [20.4] vs 58.1 [16.4] dB; P = .59), and mean AzBio score (percentage correct, 11.1% [13.3%] vs 8.0% [11.5%]; P = .25). At last follow-up (SLW vs SME, 9.0 [2.9] vs 9.9 [2.6] months), postoperative mean AzBio scores in quiet were not significantly different (percentage correct, 70.8% [21.3%] vs 65.6% [24.5%]; P = .29), and data log usage was similar (12.9 [4.0] vs 11.3 [4.1] hours; P = .07). In patients with preoperative AzBio <10% correct, the 6-month mean AzBio scores were significantly better with SLW than SME (percentage correct, 70.6% [22.9%] vs 53.9% [30.3%]; P = .02). The intraoperative tip rollover rate was 8% for SME and 0% for SLW.

CONCLUSIONS

Cochlear implantation with SLW and SME provides comparable improvement in audiologic functioning. SME does not exhibit superior speech recognition outcomes when compared with SLW.

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.

Initial hearing preservation outcomes of cochlear implantation with a slim perimodiolar electrode array

OBJECTIVE

To assess the slim modiolar array as a hearing preservation electrode.

METHODS

Retrospective chart review of adult, post-lingual CI recipients implanted with slim modiolar array Sept 2016 to July 2017 in a tertiary referral center. Baseline audiograms were obtained within six months of initial CI evaluation. Patients with low frequency pure tone average (LFPTA) (125, 250, 500 Hz) <80 dB were considered HP candidates. Postoperative audiograms were obtained within 48 h before activation. Successful HP was considered as (1) retention of LFPTA threshold <80 dB and (2) change in threshold from pre- to post-operative.

RESULTS

Sixty-three patients received the slim perimodiolar array and 42 were HP candidates. Post-operative audiograms were obtained for 39 of 42 patients an average of 28.92 days after surgery. 56.4% of HP candidates retainedLFPTA <80 dB. Mean ΔLFPTA was 24.15 dB (±16.14; p < 0.001). 56.4% of HP candidates experienced Δ LFPTA <20 dB; 69.2% <30 dB. Functional hearing preservation was more successful in lower frequencies where starting thresholds were better - 78% with LFPTA <50 dB retained serviceable hearing at activation. The postoperative change was similar in each low frequency (Δ125 Hz: mean 21.25 +/- 14.76 (N = 28); Δ250 Hz: 26.28 +/- 19.29 (N = 39); Δ500 Hz: 25.00 +/- 17.73 (N = 39)).

CONCLUSIONS

The slim perimodiolar array is moderately effective at immediate hearing preservation. In subjects with preoperative audiometric profiles similar to those in prior EAS trials, immediate HP is comparable.

Synchrotron radiation X-ray microtomography for the visualization of intra-cochlear anatomy in human temporal bones implanted with a perimodiolar cochlear implant electrode array

Recently, synchrotron radiation computed microtomography (SRµCT) has emerged as a promising tool for non-destructive, in situ visualization of cochlear implant electrode arrays inserted into a human cochlea. Histological techniques have been the `gold standard' technique for accurate localization of cochlear implant electrodes but are suboptimal for precise three-dimensional measurements. Here, an SRµCT experimental setup is proposed that offers the benefit of a high spatial and contrast resolution (isotropic voxel size = 4.95 µm and propagation-based phase-contrast imaging), while visualizing the soft-tissue structures and electrode array of the cochlear implant simultaneously. In this work, perimodiolar electrode arrays have been tested, which incorporate thick and closely spaced platinum-iridium contacts and wiring. These data can assist cochlear implant and hearing research, can be used to verify electrode segmentation techniques for clinical computed tomography or could be utilized to evaluate cochlear implant electrode array designs.

Radiological evaluation of a new straight electrode array compared to its precursors

Objective

The aim of this study is to examine electrode array coverage, scalar position and dislocation rate in straight electrode arrays with special focus on a new electrode array with 26 mm in lengths.

Study design

Retrospective study.

Setting

Tertiary academic center.

Patients

201 ears implanted between 2013 and 2019.

Main outcome measures

We conducted a comparative analysis of patients implanted with lateral wall electrode arrays of different lengths (F24 = MED-EL Flex²⁴, F26 = MED-EL Flex²⁶, F28 = MED-EL Flex²⁸ and F31.5 = MED-EL Flex^Soft). Cone beam computed tomography was used to determine electrode array position (scala tympani (ST) versus scala vestibuli (SV), intracochlear dislocation, position of dislocation and insertion angle).

Results

Study groups show no significant differences regarding cochlear size which excludes influences by cochlear morphology. As expected, the F24 showed significant shorter insertion angles compared to the longer electrode arrays. The F26 electrode array showed no signs of dislocation or SV insertion. The electrode array with the highest rate of ST dislocations was the F31.5 (26.3%). The electrode array with the highest rates of SV insertions was the F28 (5.75%). Most of the included electrode arrays dislocate between 320° and 360° (mean: 346.4°; range from 166° to 502°).

Conclusion

The shorter F24 and the new straight electrode array F26 show less or no signs of scalar dislocation, neither for round window nor for cochleostomy insertion than the longer F28 and the F31.5 array. As expected, the cochlear coverage is increasing with length of the electrode array itself but with growing risk for scalar dislocation and with the highest rates of dislocation for the longest electrode array F31.5. Position of intracochlear dislocation is in the apical cochlear part in the included lateral wall electrode arrays.

Simpler and effective radiological evaluations for modiolar proximity of a slim modiolar cochlear implant electrode

A new slim modiolar electrode (CI532/632) has been reported to ensure better modiolar proximity than conventional electrodes. Better modiolar proximity has been proposed to yield better electrode discrimination capability and potentially better speech outcomes, necessitating its efficient measurement. Currently, intracochlear positional index (ICPI), the most reliable indicator for evaluating modiolar proximity, has been measured exclusively through ‘metal artifact-less’ cone beam CT. However, popular use of this index is precluded due to lack of cone beam CT in many institutions. Thus, eyes are now on elucidation of easy-to-measure indicators of modiolar proximity derived from conventional CT, which is accessible in all centers. We observed that enhanced tomographic resolution significantly reduces partial volume artifacts, providing better visualization of modiolus-electrode distance. Aided by ultra-high kernel specification with high-resolution index, we developed a novel and easy-to-measure, conventional CT-specific indicator, “modified ICPI”, for evaluation of modiolar proximity. Further, we showed that it closely correlates with the previously proposed parameter of modiolar proximity, the spiral diameter, measured from post-insertion radiograph, reiterating the value of X-ray-based spiral diameter. Through this study, we have taken a step toward the stage of immediate visual feedback regarding modiolar proximity and changes in insertion technique intraoperatively, ensuring optimal modiolar proximity.

Immediate and 1-Year Outcomes with a Slim Modiolar Cochlear Implant Electrode Array

OBJECTIVE

To explore the immediate and 1-year outcomes of patients who underwent implantation with the slim modiolar electrode (SME).

STUDY DESIGN

Consecutive case series with chart review.

SETTING

Tertiary referral academic center.

SUBJECT AND METHODS

Between May 2016 and August 2018, a total of 326 cochlear implantations (CIs) were performed. Intraoperative x-rays were performed in all cases to identify tip rollovers. Scalar location was identified for 76 CIs that had postoperative computed tomography reconstructions. Speech outcomes were measured at 3, 6, and 12 months with consonant-nucleus-consonant word and AzBio sentences in quiet and noise (+10-dB signal-to-noise ratio). Preservation of hearing was defined as maintaining a low-frequency pure tone average ≤80 dB at 250 and 500 Hz.

RESULTS

Among 326 CIs, 23 (7%) had tip rollovers. Postoperative reconstructions revealed 5 of 76 (6.6%) scalar translocations. A subset of 177 cases met criteria for evaluation of speech perception scores. The marginal mean differences between presurgery and 12 months for speech tests were as follows: consonant-nucleus-consonant, 43.7 (95% CI, 39.8-47.6); AzBio in quiet, 49.7 (95% CI, 44.9-54.4); and AzBio in noise, 29.9 (95% CI, 25.2-34.7). Sixty-one patients were identified with preservable hearing (low-frequency pure tone average ≤80 dB), and 12 of 61 (20%) preserved hearing at 1 year.

CONCLUSION

CI with SME provides reliable scala tympani insertion in a consistent perimodiolar position. An initially increased tip rollover rate improved with case volume and sheath design improvement. For long-term outcomes, speech performance was comparable to that of other cochlear implants. While hearing preservation for the SME may be better than prior perimodiolar electrodes, consistent outcomes are unlikely.

A New Application of CBCT Image Fusion in Temporal Bone Studies

OBJECTIVES

Temporal bone (TB) studies are essential during the development of new arrays. Postoperative cochlear histology is still regarded as golden standard for the assessment of electrode localization and trauma though it is time consuming, expensive and technically very demanding. The aim of this study is to investigate whether pre-operative evacuation of perilymph improve the assessment of electrode localization and insertion trauma in TBs applying fusion imaging. The results were compared to a prior validated image fusion technique based on the quantification of the electrode placement.

MATERIALS AND METHODS

12 prototype electrodes were implanted in fresh frozen TBs. The perilymph was evacuated from the scale prior to pre-operative cone-beam computer tomography (CBCT). The TB were then immersed in Ringer solution to rehydrated both scalae. After electrode insertion post-operative CBCT were obtained. 3D fusions of the pre- and postoperative registration were reconstructed. The electrode localization with respect to the basilar membrane was visually assessed.

RESULTS

The visualization of the BM on the pre-operative scans was achieved beyond the second turn in all TBs. The visual assessment was found to be as accurate as the previously validated fusion technique. There was no statistically significant difference between the methods (p=0.564). The image reconstructions and evaluations, however, were faster to perform and the insertion results are immediately available.

CONCLUSION

CBCT in combination with pre- and postoperative image fusion is an accurate method for the post-operative assessment of insertion trauma in TBs. This new application facilitates the identification of the BM and allows for a visual assessment of insertion trauma.

The Image Fusion Technique for Cochlear Implant Imaging: A Study of its Application for Different Electrode Arrays

OBJECTIVES

To investigate the benefits of the image fusion technique for precise postoperative assessment of intracochlear placement with six different electrode arrays.

STUDY DESIGN

Consecutive retrospective case study.

SETTINGS

Tertiary referral center.

PATIENTS

Analyses of imaging data of 30 patients implanted with six different electrode arrays.

INTERVENTIONS

Electrode reconstructions obtained from postoperative cone-beam computed tomography (CBCT) were overlaid onto preoperative magnetic resonance imaging (MRI) and/or high-resolution computed tomography (HRCT) registrations to create artefact-free images.

MAIN OUTCOME MEASURES

Each electrode's intracochlear position was analyzed with the image fusion reconstructions and compared with the results obtained by CBCT alone. The electrode location was classified according to its position in relation to the basal membrane at four different insertion angles.

RESULTS

In 40 out of 151 measurements (26.5%), the location grading obtained by CBCT alone changed after the assessment with the image fusion reconstructions. A significant association was found between deep insertions (over 360 degrees) and the effectiveness of image fusion (p = 0.019). The difference between the impact of the fusion technique for the basal turn versus the apical part was highly significant (p = 0.001). There was no significant difference between the effectiveness of the image fusion and the different electrodes.

CONCLUSIONS

By utilizing an image fusion technique, a more accurate assessment of electrode placement could be achieved for all types of electrodes. Image fusion was especially beneficial for insertions beyond 360 degrees.

The Insertion Results of a Mid-scala Electrode Assessed by MRI and CBCT Image Fusion

OBJECTIVES

To investigate the results of clinical surgical insertions with a Mid-scala array (HIFocus Mid-Scala Electrode, HFms).

STUDY DESIGN

Consecutive retrospective case study.

SETTINGS

Tertiary referral center.

PATIENTS

Analyses of imaging data of 26 consecutive patients (31 insertions) implanted with the HFms.

INTERVENTION (S)

The evaluation of insertion trauma evoked by a previously validated image fusion technique. Electrode reconstructions from postoperative cone-beam computed tomography (CBCT) were overlaid onto preoperative magnetic resonance imaging (MRI) scans to create artifact-free images.

MAIN OUTCOME MEASURES

The electrode position was quantified in relation to the basilar membrane. Trauma scaling adopted from Eshraghi was used for evaluating insertion trauma. The results of the visual assessment of the postoperative CBCT were compared to those obtained with the fusion technique.

RESULTS

Three insertions had to be excluded due to incompatibility of the imaging data with the fusion software. We found consistent peri- to mid-modiolar placement of the HFms with a mean insertion depth angle of 376°. According to the medical records, a visual examination of the postoperative CBCT indicated that there had been no scala dislocations but when assessed by the image fusion technique, five scala dislocations (17.8%) were found. Additionally, one tip fold-over was detected in the postoperative CBCT even though this was not evident in any intraoperative measurements.

CONCLUSION

HFms showed atraumatic surgical insertion results with consistent mid-modiolar placement. Image fusion enhances the accuracy of the insertion trauma assessment. Routine postoperative imaging is recommended for identifying tip fold-over as well as for quality control and documentation.

Cochlear Implantation With a Novel Long Straight Electrode: the Insertion Results Evaluated by Imaging and Histology in Human Temporal Bones

HYPOTHESIS

To evaluate the insertion results of a novel straight array (EVO) by detailed imaging and subsequent histology in human temporal bones (TB).

BACKGROUND

The main focuses of modern cochlear implant surgery are to prevent damage to the intracochlear structures and to preserve residual hearing. This is often achievable with new atraumatic electrode arrays in combination with meticulous surgical techniques.

METHODS

Twenty fresh-frozen TBs were implanted with the EVO. Pre- and postoperative cone beam computed tomography scans were reconstructed and fused for an artifact-free representation of the electrode. The array's vertical position was quantified in relation to the basilar membrane on basis of which trauma was classified (Grades 0-4). The basilar membrane location was modeled from previous histologic data. The TBs underwent subsequent histologic examination.

RESULTS

The EVOs were successfully inserted in all TBs. Atraumatic insertion (Grades 0-1) were accomplished in 14 of 20 TBs (70%). There were three apical translocations, and two basal translocations due to electrode bulging. One TB had multiple translocations. The sensitivity and specificity of imaging for detecting insertion trauma (Grades 2-4) was 87.5% and 97.3.0%, respectively.

CONCLUSION

Comparable insertion results as reported for other arrays were also found for the EVO. Insertion trauma can be mostly avoided with meticulous insertion techniques to prevent bulging and by limiting the insertion depth angle to 360 degrees. The image fusion technique is a reliable tool for evaluating electrode placement and is feasible for trauma grading.

Preservation of residual hearing after cochlear implant surgery with slim modiolar electrode

Purpose

To evaluate the insertion results and hearing preservation of a novel slim modiolar electrode (SME) in patients with residual hearing.

Methods

We retrospectively collected the data from the medical files of 17 patients (18 ears) implanted with a SME. All patients had functional low frequency hearing (PTA _{(0.125–0.5 kHz)} ≤ 80 dB HL). The insertion results were re-examined from the postoperative cone-beam computed tomography scans. Postoperative thresholds were obtained at the time of switch-on of the sound processors (mean 43 days) and at latest follow-up (mean 582 days). The speech recognition in noise was measured with the Finnish matrix sentence test preoperatively and at follow-up.

Results

The mean insertion depth angle (IDA) was 395°. Neither scala dislocations nor tip fold over were detected. There were no total hearing losses. Functional low-frequency hearing was preserved in 15/18 (83%) ears at switch-on and in 14/17 (82%) ears at follow-up. According to HEARRING classification, 55% (10/18) had complete HP at switch-on and 41% (7/17) still at follow-up. Thirteen patients (14 ears) were initially fitted with electric–acoustic stimulation and seven patients (8 ears) continued to use it after follow-up.

Conclusions

The preliminary hearing preservation results with the SME were more favorable than reported for other perimodiolar electrodes. The results show that the array may also be feasible for electro-acoustic stimulation; it is beneficial in that it provides adequate cochlear coverage for pure electrical stimulation in the event of postoperative or progressive hearing loss.

Review on cochlear implant electrode array tip fold-over and scalar deviation

Objective

Determine the occurrence rate of cochlear implant (CI) electrode tip fold-over and electrode scalar deviation as reported in patient cases with different commercial electrode types.

Data-sources

PubMed search for identifying peer-reviewed articles published till 2018 on CI electrode tip fold-over and scalar deviation. Key-words for searching were “Cochlear electrode tip fold-over”, “Cochlear electrode scalar position” and “Cochlear electrode scalar location”.

Articles-selection

Only if electrode related issues were investigated in patient cases. 38 articles met the inclusion-criteria.

Results

13 articles on electrode tip fold-over issue covering 3177 implanted ears, out of which 50 ears were identified with electrode tip fold-over with an occurrence rate of 1.57%. Out of 50 ears, 43 were implanted with pre-curved electrodes and the remaining 7 with lateral-wall electrodes. One article reported on both tip fold-over and scalar deviation. 26 articles reported on the electrode scalar deviation covering an overall number of 2046 ears out of which, 458 were identified with electrode scalar deviation at a rate of 22.38%. After removing the studies that did not report on the number of electrodes per electrode type, it was 1324 ears implanted with pre-curved electrode and 507 ears with lateral-wall electrode. Out of 1324 pre-curved electrode implanted ears, 424 were reported with scalar deviation making an occurrence rate of 32%. Out of 507 lateral-wall electrode implanted ears, 43 were associated with scalar deviation at an occurrence rate of 6.7%.

Conclusion

This literature review revealing the fact of higher rate of electrode insertion trauma associated with pre-curved electrode type irrespective of CI brand is one step closer to obsolete it from the clinical practice in the interest of patient's cochlear health.

Considerations and Rationale for Cochlear Implant Electrode Design - Past, Present and Future

The electrode array of a cochlear implant forms a permanent, often lifelong interface between the implanted electronics and neural structures of the cochlea. A cochlear implant is primarily prescribed to restore hearing via electrical stimulation of the auditory nerve. As with any neural stimulator intended to either deliver electrical stimulus or record a neural response, the aim is to place the electrodes in close proximity to the target neural structures. The broadening of indications and the concept of preservation of low-frequency residual hearing over the last two decades has resulted in an increased understanding of the mechanisms and implications of intracochlear trauma for both the hearing preservation surgery and electrical stimulation outcomes with cochlear implantation, as well as the influence of many biographic and audiological patient factors correlated with achieving better hearing outcomes. These two goals, the proximity to the cochlear nerve for electrical stimulation and the preservation of cochlear structures, have typically been viewed as mutually exclusive, with perimodiolar electrode arrays being preferred for the former, and lateral wall electrode arrays for the latter. The design evolution of both the lateral wall and perimodiolar electrodes is presented, considering the cochlea anatomy and continued understanding of the mechanics and dynamics of electrode insertion, along with the influence of the ongoing changes to the intracochlear environment to provide a rationale for the electrode design with the intent to provide the greatest patient benefit over their implanted lifetime.

Imaging evaluation of electrode placement and effect on electrode discrimination on different cochlear implant electrode arrays

OBJECTIVE

The aim of the present study is to evaluate the effect of electrode discrimination based on electrode to modiolus distance in different cochlear implant models, using image information to estimate the outcomes after an implantation on electrode discrimination METHODS: A descriptive prospective randomized study performed during 16 months. A psychoacoustic platform was used to evaluate patients' electrode discrimination capabilities of patients. For the acquisition of the images, a cone beam computed tomography was used to assess postcochlear implantation of electrodes' position. We considered two other new measurements: the intracochlear position index, which indicates how far is the electrode from the modiolar wall, and the homogeneity factor (HF), which provides us with information about the distance between the electrodes and the modiolus RESULTS: 21 postlingually deaf adults showing different CI models [CI522 (n = 7), CI512 (n = 7), and CI532 (n = 7)] that corresponded to the lateral and perimodiolar array electrodes. The average success rate of the CI522 group was 47%, of the CI512 group was 48%, and of the CI532 group was 77%. There is statistically significant difference between groups CI532-CI522 (p = 0.0033) and CI532-CI512 (p = 0.0027) CONCLUSION: The Nucleus CI532 offers a better perimodiolar placement. HF and IPI measurements provide information about the electrodes location inside the cochlea, being related to electrode discrimination.