Relations Between Scalar Shift and Insertion Depth in Human Cochlear Implantation

Systematic Review of Intracochlear Measurements and Effect on Postoperative Auditory Outcomes after Cochlear Implant Surgery

OBJECTIVE

Quality and adequacy of the electrode neuron interface (ENI) is postulated to be a determining factor in affecting auditory outcomes after cochlear implantation. This study aims to review radiological parameters affecting ENI, including angular insertion (AngI), wrapping factor (WF), scalar translocation (ScaT), and electrode-modiolar distance (EMD) and their effect on auditory outcomes.

DATABASES REVIEWED

PubMed, MEDLINE, Embase, Scopus, OpenGrey, and Google Scholar from inception to 01 September 2022.

METHODS

Inclusion criteria were (i) all humans with any cochlear implant (CI); (ii) postoperative cross-sectional imaging with electrode position factors of AngI, ScaT, EMD, and/or WF; and (iii) associated auditory outcomes. Search was restricted to English-language literature. Two independent reviewers performed title and abstract screening, data extraction, and ROBINS-I risk of bias assessment. Formal statistical analysis not performed due to data heterogeneity. PROSPERO (CRD42022359198).

RESULTS

Thirty-one studies (n = 2,887 patients, 3,091 electrodes) underwent qualitative synthesis. Higher AngI (n = 1921 patients) demonstrated positive correlation in 11 studies, no correlation in eight studies, and negative correlation in four studies. ScaT (n = 2,115 patients) demonstrated negative correlation in 12 studies, none in six studies, and one unclear correlation. Larger EMD (n = 240 patients) showed negative correlation in two studies, no correlation in one, and unclear correlation in one study. Smaller WF (n = 369 patients) demonstrated no correlation in three studies and positive correlation in one study.

CONCLUSIONS

Our study finds variable reported relationship between AngI and auditory outcomes. CI electrodes with a ScaT or larger EMD are more likely to exhibit poorer outcomes, and WF does not correlate with outcomes.

The effect of the surgical approach and cochlear implant electrode on the structural integrity of the cochlea in human temporal bones

Cochlear implants (CI) restore hearing of severely hearing-impaired patients. Although this auditory prosthesis is widely considered to be very successful, structural cochlear trauma during cochlear implantation is an important problem, reductions of which could help to improve hearing outcomes and to broaden selection criteria. The surgical approach in cochlear implantation, i.e. round window (RW) or cochleostomy (CO), and type of electrode-array, perimodiolar (PM) or lateral wall (LW), are variables that might influence the probability of severe trauma. We investigated the effect of these two variables on scalar translocation (STL), a specific type of severe trauma. Thirty-two fresh frozen human cadaveric ears were evenly distributed over four groups receiving either RW or CO approach, and either LW or PM array. Conventional radiological multiplanar reconstruction (MPR) was compared with a reconstruction method that uncoils the spiral shape of the cochlea (UCR). Histological analysis showed that RW with PM array had STL rate of 87% (7/8), CO approach with LW array 75% (6/8), RW approach with LW array 50% (4/8) and CO approach with PM array 29% (2/7). STL assessment using UCR showed a higher inter-observer and histological agreement (91 and 94% respectively), than that using MPR (69 and 74% respectively). In particular, LW array positions were difficult to assess with MPR. In conclusion, the interaction between surgical approach and type of array should be preoperatively considered in cochlear implant surgery. UCR technique is advised for radiological assessment of CI positions, and in general it might be useful for pathologies involving the inner ear or other complex shaped bony tubular structures.

Functional Outcomes and Quality of Life after Cochlear Implantation in Patients with Long-Term Deafness

Background: Hearing-related quality of life (QoL) after cochlear implantation (CI) is as important as audiological performance. We evaluated the functional results and QoL after CI in a heterogeneous patient cohort with emphasis on patients with long-term deafness (>10 years). Methods: Twenty-eight patients (n = 32 implanted ears, within n = 12 long-term deaf ears) implanted with a mid-scala electrode array were included in this retrospective mono-centric cohort study. Speech intelligibility for monosyllables (SIM), speech reception thresholds (SRT50) and QoL with Nijmegen Cochlear Implant Questionnaire (NCIQ) were registered. Correlation of SIM and QoL was analyzed. Results: SIM and SRT50 improved significantly 12 months postoperatively up to 54.8 ± 29.1% and 49.3 ± 9.6 dB SPL, respectively. SIM progressively improved up to 1 year, but some early-deafened, late implanted patients developed speech understanding several years after implantation. The global and all subdomain QoL scores increased significantly up to 12 months postoperatively and we found a correlation of SIM and global QoL score at 12 months postoperatively. Several patients of the “poor performer” (SIM < 40%) group reported high improvement of hearing-related QoL. Conclusions: Cochlear implantation provides a benefit in hearing-related QoL, even in some patients with low postoperative speech intelligibility results. Consequently, hearing-related QoL scores should be routinely used as outcome measure beside standard speech understanding tests, as well. Further studies with a prospective multi-centric design are needed to identify factors influencing post-implantation functional results and QoL in the patient group of long-term deafness.

Assessing the Placement of the Cochlear Slim Perimodiolar Electrode Array by Trans Impedance Matrix Analysis: A Temporal Bone Study

New cochlear implant (CI) electrode arrays provide softer insertion dynamics; however, due to their high flexibility, the possibilities of fold-overs or intraoperative displacements must be taken into account. The position of each individual electrode can only be determined by using high-resolution computed tomography or cone-beam CT. The trans-impedance matrix test (TIM) is an electrophysiological method based on electric field imaging that can provide images of electrode position and electrode folding. Objective: In this experimental research, we evaluated the result of TIM as a method of monitoring cochlear insertion for a precurved slim modiolar electrode array in fresh human temporal bones by analyzing the transimpedance matrix patterns and their correlation with electrode position using high-resolution computed tomography. Material and Methods: Sixteen slim modiolar electrode arrays were inserted into eight fresh Human Temporal Bones. Eight electrodes were inserted according to the correct methodology of insertion, and eight were intentionally folded over. After all insertions, a trans-impedance matrix analysis and a Cone Beam CT (CBCT) were performed in each temporal bone. Results: If we correlated the TIM patterns with the radiological electrode position, we observed that better electrode intracochlear positions indicated more “homogeneous” TIM patterns (intracochlear voltage dropped monotonically as the distance between stimulation and recording contact increased, both toward the apex and toward the base). A correlation where fold-over was detected in the TIM results was found in all eight temporal bone radiological findings. Conclusions: Trans-Impedance Matrix patterns were correlated with the radiological CI electrode position. When a tip fold-over appeared, a matrix with a secondary ridge in addition to the primary ridge was observed in all cases. TIM can be an effective method in the control of electrode positioning.

Intracochlear New Fibro-Ossification and Neuronal Degeneration Following Cochlear Implant Electrode Translocation: Long-Term Histopathological Findings in Humans

OBJECTIVE

We aim to assess the histopathology of human temporal bones (TBs) with evidence of cochlear implantation (CI) electrode scalar translocation.

STUDY DESIGN

Otopathology study.

SETTING

Otopathology laboratory.

PATIENTS

TBs from patients who had a history of CI and histopathological evidence of interscalar translocation. Specimens with electrode placed entirely within the ST served as controls.

INTERVENTION

Histopathological assessment of human TBs.

MAIN OUTCOME MEASURES

TBs from each patient were harvested postmortem and histologically analyzed for intracochlear changes in the context of CI electrode translocation and compared to controls. Intracochlear new fibro-ossification, and spiral ganglion neuron (SGN) counts were assessed. Postoperative word recognition scores (WRS) were also compared.

RESULTS

Nineteen human TBs with electrode translocation and eight controls were identified. The most common site of translocation was the ascending limb of the basal turn (n = 14 TBs). The average angle of insertion at the point of translocation was 159° ± 79°. Eighteen translocated cases presented moderate fibroosseous changes in the basal region of the cochlea, extending to the translocation point and/or throughout the electrode track in 42%. Lower SGN counts were more pronounced in translocated cases compared to controls, with a significant difference for segment II (p = 0.019). Although final postoperative hearing outcomes were similar between groups, translocated cases had slower rate of improvement in WRS (p = 0.021).

CONCLUSIONS

Cochlear implant electrode translocation was associated with greater fibroosseous formation and lower SGN population. Our findings suggest that scalar translocations may slow the rate of improvement in WRS overtime as compared to atraumatic electrode insertions.Level of evidence: IV.

Hybrid active shape and deep learning method for the accurate and robust segmentation of the intracochlear anatomy in clinical head CT and CBCT images

Purpose: Robust and accurate segmentation methods for the intracochlear anatomy (ICA) are a critical step in the image-guided cochlear implant programming process. We have proposed an active shape model (ASM)-based method and a deep learning (DL)-based method for this task, and we have observed that the DL method tends to be more accurate than the ASM method while the ASM method tends to be more robust. Approach: We propose a DL-based U-Net-like architecture that incorporates ASM segmentation into the network. A quantitative analysis is performed on a dataset that consists of 11 cochlea specimens for which a segmentation ground truth is available. To qualitatively evaluate the robustness of the method, an experienced expert is asked to visually inspect and grade the segmentation results on a clinical dataset made of 138 image volumes acquired with conventional CT scanners and of 39 image volumes acquired with cone beam CT (CBCT) scanners. Finally, we compare training the network (1) first with the ASM results, and then fine-tuning it with the ground truth segmentation and (2) directly with the specimens with ground truth segmentation. Results: Quantitative and qualitative results show that the proposed method increases substantially the robustness of the DL method while having only a minor detrimental effect (though not significant) on its accuracy. Expert evaluation of the clinical dataset shows that by incorporating the ASM segmentation into the DL network, the proportion of good segmentation cases increases from 60/177 to 119/177 when training only with the specimens and increases from 129/177 to 151/177 when pretraining with the ASM results. Conclusions: A hybrid ASM and DL-based segmentation method is proposed to segment the ICA in CT and CBCT images. Our results show that combining DL and ASM methods leads to a solution that is both robust and accurate.

Atraumatic Insertion of a Cochlear Implant Pre-Curved Electrode Array by a Robot-Automated Alignment with the Coiling Direction of the Scala Tympani

INTRODUCTION

Electrode array translocation is an unpredictable event with all types of arrays, even using a teleoperated robot in a clinical scenario. We aimed to compare the intracochlear trauma produced by the HiFocus™ Mid-Scala (MS) electrode array (Advanced Bionics, Valencia, CA, USA) using a teleoperated robot, with an automated robot connected to a navigation system to align the pre-curved tip of the electrode array with the coiling direction of the scala tympani (ST).

METHODS

Fifteen freshly frozen temporal bones were implanted with the MS array using the RobOtol® (Collin, Bagneux, France). In the first group (n = 10), the robot was teleoperated to insert the electrode array into the basal turn of the ST under stereomicroscopic vision, and then the array was driven by a slow-speed hydraulic insertion technique with an estimated placement of the pre-curved electrode tip. In the second group (n = 5), 3 points were obtained from the preoperative cone-beam computed tomography: the 2 first defining the ST insertion axis of the basal turn and a third one at the center of the ST at 270°. They provided the information to the automated system (RobOtol® connected with a navigation system) to automatically align the electrode array with the ST insertion axis and to aim the pre-curved tip toward the subsequent coiling of the ST. After this, the electrode array was manually advanced. Finally, the cochleae were obtained and fixed in a crystal resin, and the position of each electrode was determined by a micro-grinding technique.

RESULTS

In all cases, the electrode array was fully inserted into the cochlea and the depth of insertion was similar using both techniques. With the teleoperated robotic technique, translocations of the array were observed in 7/10 insertions (70%), but neither trauma nor array translocation occurred with automated robotic insertion.

CONCLUSION

We have successfully tested an automated insertion system (robot + navigation) that could accurately align a pre-curved electrode array to the axis of the basal turn of the ST and its subsequent coiling, which reduced intracochlear insertion trauma and translocation.

Scalar Translocation Comparison Between Lateral Wall and Perimodiolar Cochlear Implant Arrays - A Meta-Analysis

Objectives/Hypothesis

Two types of electrode arrays for cochlear implants (CIs) are distinguished: lateral wall and perimodiolar. Scalar translocation of the array can lead to intracochlear trauma by penetrating from the scala tympani into the scala vestibuli or scala media, potentially negatively affecting hearing performance of CI users. This systematic review compares the lateral wall and perimodiolar arrays with respect to scalar translocation.

Study Design

Systematic review.

Methods

PubMed, Embase, and Cochrane databases were reviewed for studies published within the last 11 years. No other limitations were set. All studies with original data that evaluated the occurrence of scalar translocation or tip fold‐over (TF) with postoperative computed tomography (CT) following primary cochlear implantation in bilateral sensorineuronal hearing loss patients were considered to be eligible. Data were extracted independently by two reviewers.

Results

We included 33 studies, of which none were randomized controlled trials. Meta‐analysis of five cohort studies comparing scalar translocation between lateral wall and perimodiolar arrays showed that lateral wall arrays have significantly lower translocation rates (7% vs. 43%; pooled odds ratio = 0.12). Translocation was negatively associated with speech perception scores (weighted mean 41% vs. 55%). Tip fold‐over of the array was more frequent with perimodiolar arrays (X² = 6.8, P < .01).

Conclusions

Scalar translocation and tip fold‐overs occurred more frequently with perimodiolar arrays than with lateral wall arrays. In addition, translocation of the array negatively affects hearing with the cochlear implant. Therefore, if one aims to minimize clinically relevant intracochlear trauma, lateral wall arrays would be the preferred option for cochlear implantation. Laryngoscope, 131:1358–1368, 2021