Long-term Hearing Preservation and Speech Perception Performance Outcomes With the Slim Modiolar Electrode

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.

Electrocochleography-Based Tonotopic Map: II. Frequency-to-Place Mismatch Impacts Speech-Perception Outcomes in Cochlear Implant Recipients

OBJECTIVES

Modern cochlear implants (CIs) use varying-length electrode arrays inserted at varying insertion angles within variably sized cochleae. Thus, there exists an opportunity to enhance CI performance, particularly in postlinguistic adults, by optimizing the frequency-to-place allocation for electrical stimulation, thereby minimizing the need for central adaptation and plasticity. There has been interest in applying Greenwood or Stakhovskaya et al. function (describing the tonotopic map) to postoperative imaging of electrodes to improve frequency allocation and place coding. Acoustically-evoked electrocochleography (ECochG) allows for electrophysiologic best-frequency (BF) determination of CI electrodes and the potential for creating a personalized frequency allocation function. The objective of this study was to investigate the correlation between early speech-perception performance and frequency-to-place mismatch.

DESIGN

This retrospective study included 50 patients who received a slim perimodiolar electrode array. Following electrode insertion, five acoustic pure-tone stimuli ranging from 0.25 to 2 kHz were presented, and electrophysiological measurements were collected across all 22 electrode contacts. Cochlear microphonic tuning curves were subsequently generated for each stimulus frequency to ascertain the BF electrode or the location corresponding to the maximum response amplitude. Subsequently, we calculated the difference between the stimulus frequency and the patient's CI map's actual frequency allocation at each BF electrode, reflecting the frequency-to-place mismatch. BF electrocochleography-total response (BF-ECochG-TR), a measure of cochlear health, was also evaluated for each subject to control for the known impact of this measure on performance.

RESULTS

Our findings showed a moderate correlation (r = 0.51; 95% confidence interval: 0.23 to 0.76) between the cumulative frequency-to-place mismatch, as determined using the ECochG-derived BF map (utilizing 500, 1000, and 2000 Hz), and 3-month performance on consonant-nucleus-consonant words (N = 38). Larger positive mismatches, shifted basal from the BF map, led to enhanced speech perception. Incorporating BF-ECochG-TR, total mismatch, and their interaction in a multivariate model explained 62% of the variance in consonant-nucleus-consonant word scores at 3 months. BF-ECochG-TR as a standalone predictor tended to overestimate performance for subjects with larger negative total mismatches and underestimated the performance for those with larger positive total mismatches. Neither cochlear diameter, number of cochlear turns, nor apical insertion angle accounted for the variability in total mismatch.

CONCLUSIONS

Comparison of ECochG-BF derived tonotopic electrode maps to the frequency allocation tables reveals substantial mismatch, explaining 26.0% of the variability in CI performance in quiet. Closer examination of the mismatch shows that basally shifted maps at high frequencies demonstrate superior performance at 3 months compared with those with apically shifted maps (toward Greenwood and Stakhovskaya et al.). The implications of these results suggest that electrophysiological-based frequency reallocation might lead to enhanced speech-perception performance, especially when compared with conventional manufacturer maps or anatomic-based mapping strategies. Future research, exploring the prospective use of ECochG-based mapping techniques for frequency allocation is underway.

Hearing preservation in paediatric cochlear implantation with the Nucleus Slim Straight Electrode - our experience

OBJECTIVE

to evaluate the levels of successful hearing preservation and preservation of functional hearing following cochlear implantation (HPCI) in children using the Cochlear Nucleus® Slim Straight Electrode (SSE).

DESIGN

retrospective case note review of paediatric HPCI cases in our CI centre from 2013 to 2023. Inclusion criteria were attempted hearing preservation surgery, SSE used for implantation, pre-operative hearing thresholds ≤80dBHL at 250 Hz, CI before 18 years of age. Patients were excluded if no postoperative unaided PTA was obtained (poor attendance). Primairy outcome was hearing preservation using the HEARRING group formula; secondary outcome was residual functional hearing (≤80dBHL at 250 Hz/<90dB LFPTA).

STUDY SAMPLE

56 patients with 94 CI's were included for review.

RESULTS

Hearing preservation was achieved in 94.7% (89/94) of ears and complete preservation in 72% (68/94)). Average functional hearing was preserved in 89% using both criteria for preservation. Long-term follow up data was available for 36 ears (average 35.2 months), demonstrating 88.9% (32/36) complete preservation.

CONCLUSION

We have reliably achieved and maintained a high success rate of HPCI using the SSE in our paediatric population. The field of HPCI would benefit from unification of outcome reporting in order to optimise the evidence available to professionals, patients and their carers.

Two Discrete Types of Tip Fold-Over in Cochlear Implantation Using Slim Modiolar Electrodes: Influence of Cochlear Duct Length on Tip Fold-Over

OBJECTIVE

Precise electrode positioning is crucial for achieving optimal audiological outcomes in cochlear implantation. The slim modiolar electrode (SME), a thin, flexible, and precurved electrode, exhibits favorable modiolar proximity. However, tip fold-over can affect optimal electrode placement. Herein, we share our experiences with tip fold-over in SMEs and present an analysis of conditions that may predispose to tip fold-over.

STUDY DESIGN

Retrospective medical record review.

PATIENTS

In total, 475 patients (671 ears) underwent cochlear implantation using SMEs (Nucleus CI532 or CI632 from Cochlear) performed by a single surgeon at a tertiary center between June 14, 2018, and December 1, 2022.

INTERVENTIONS

Intraoperative x-ray scans (cochlear view), operative records, and cochlear duct length (CDL) were reviewed.

MAIN OUTCOME MEASURES

Tip fold-over patterns on plain x-ray images (proximal versus distal).

RESULTS

Electrode tip fold-over was observed in 18 (2.7%) of the 671 ears with SMEs. This fold-over occurred more frequently in cases with long CDL (>36 mm). Among the 14 cases with available initial x-rays before correction of the tip fold-over, half were classified as proximal and the other half as distal. A predilection for proximal tip fold-over was found in those with a CDL of 36 mm or longer, and longer CDLs were observed for proximal cases than for distal cases. Our pilot data suggest that identifying the type of tip fold-over can aid in correcting it more efficiently.

CONCLUSIONS

Tip fold-over of SME does not occur uniformly and is more common in ears with long CDL. This tendency is particularly pronounced for the proximal type of tip fold-over. Therefore, preoperative measurement of the CDL and meticulous examination of intraoperative imaging are essential for customized correction.

One-Year Hearing Preservation and Speech Outcomes Comparing Slim Modiolar and Lateral Wall Arrays

OBJECTIVE

Compare postoperative speech outcomes in hearing preservation (HP) cochlear implantation (CI) patients with a low-frequency pure-tone average (LFPTA) ≤ 60 dB using 2 electrode array designs.

STUDY DESIGN

Retrospective cohort study.

SETTING

Large academic cochlear implant referral center.

METHODS

We reviewed adult HP CI cases using either the slim modiolar electrode (SME) (CI 532/CI 632) or th slim lateral wall electrode (SLWE) (CI 624). One-year speech outcomes and HP status were the primary outcomes.

RESULTS

A total of 132 implanted ears were analyzed (mean age 73.1 years, standard deviation [SD] 12.6), with 72% (N = 95) with CI 532/632 and 28% (N = 37) with CI 624. The mean preoperative LFPTA was 44.8 dB, SD 11.8. One-year functional HP was 27.2% (mean LFPTA shift 46.1 dB, SD 22.1) and was as follows: SME 23.9% and SLWE 36.4%, p = .168. The mean age at implantation was significantly younger only in SLWE patients with preserved hearing (66.9 vs 80.3 years, p = .008). At 6 months, speech measures were significantly better in all outcomes in HP patients with an SLWE than nonpreserved SLWE patients; this effect abated at 1 year as performance among nonpreserved SLWE patients became equivalent to the remaining cohort. Speech outcomes in SME patients were similar regardless of HP status. Age at implantation and datalogging was correlated with speech outcomes.

CONCLUSION

In this cohort of HP patients, a 1-year functional HP rate of 23.9% (SME) and 36.4% (SLWE) was observed (p = 0.168). This was initially 57.1% (SME) and 70.3% (SLWE) at activation, p = .172. Datalogging and age at implantation were correlated with postoperative speech outcomes.

Deep intracochlear injection of triamcinolone-acetonide with an inner ear catheter in patients with residual hearing

Introduction

In a previous study, an inner ear catheter was used to deliver low- and high-dose steroids into the cochlea prior to cochlear implant electrode insertion. With this approach, more apical regions of the cochlea could be reached and a reduction of electrode impedances in the short term was achieved in cochlear implant recipients. Whether intracochlear application of drugs via the catheter is a safe method also for patients with residual hearing has not been investigated hitherto. The aim of the present study was therefore to investigate the effect of intracochlear triamcinolone application in cochlear implant recipients with residual hearing.

Patients and methods

Patients with residual hearing were administered triamcinolone-acetonide (4 mg/ml; n = 10) via an inner ear catheter just prior to insertion of a MED-EL FLEX28 electrode. Impedances were measured at defined time points (intra-operatively, post-operatively and at first fitting) and retrospectively compared with a control group (no steroid application) and low- and high-dose group. Hearing thresholds were measured preoperatively, 3 days after surgery and at first fitting by pure tone audiometry. Pre- to postoperative hearing loss was determined at first fitting and compared to results from a previous study.

Results

The median hearing loss after implantation (125-1,500 Hz) was 20.6 dB. Four patients (40%) showed a median hearing loss of less than 15 dB, three patients (30%) between 15 and 30 dB and three patients (30%) more than 30 dB. The median hearing loss was similar to the results obtained from our previous study showing a median hearing loss of 24 dB when using FLEX28 electrode arrays.

Conclusion

No difference in residual hearing loss was found when comparing application of triamcinolone-acetonide using an inner ear catheter prior to the insertion of a FLEX28 electrode array to the use of the FLEX28 electrode array without the catheter. Thus, we conclude that application of drugs to the cochlea with an inner ear catheter could be a feasible approach in patients with residual hearing.

A new paradigm of hearing loss and preservation with cochlear implants: Learnings from fundamental studies and clinical research

In 2010 Cochlear initiated a coordinated preclinical research program to identify the factors and underlying mechanisms of acoustic hearing loss following cochlear implantation and device use. At its inception the program was structured around several major hypotheses implicated in the loss of acoustic hearing. The understanding of causes evolved over the course of the program, leading to an increased appreciation of the role of the biological response in post-implant hearing loss. A systematic approach was developed which mapped the cochlear implant journey along a timeline that considers all events in an individual's hearing history. By evaluating the available data in this context, rather than by discrete hypothesis testing, causative and associated factors may be more readily detected. This approach presents opportunities for more effective research management and may aid in identifying new prospects for intervention. Many of the outcomes of the research program apply beyond preservation of acoustic hearing to factors important to overall cochlear health and considerations for future therapies.

Detection of Tip Fold-Over of the Slim Modiolar Electrode Using Intraoperative Mobile Cone-Beam Computed Tomography

OBJECTIVE

This study aimed to evaluate the importance of mobile cone-beam computed tomography in detecting tip fold-over of a slim modiolar electrode within the cochlea during surgery.

STUDY DESIGN

Retrospective case review.

SETTING

Tertiary medical center.

METHODS

From January 2020 to June 2022, 33 ears of 30 patients with normal cochlear morphology underwent cochlear implantation with slim modiolar electrodes and intraoperative mobile cone-beam computed tomography imaging. Furthermore, we retrospectively reviewed the medical records and images.

RESULTS

The tip fold-over of the electrodes was detected using mobile cone-beam computed tomography in 3 out of 33 ears (9.1%). We could not identify the tip fold-over by scouting plain X-ray images in 2 out of 3 cases before taking the cone-beam computed tomography images. Electrode removal and reinsertion were performed before wound closure and the successful reinsertion was confirmed by mobile cone-beam computed tomography. The folded electrode tips were located at 238.8°, 152°, and 185.8°.

CONCLUSION

Intraoperative mobile cone-beam computed tomography is useful in detecting the tip fold-over of the slim modiolar electrodes during surgery. Therefore, it was possible to reinsert the electrodes in all cases before closing the wound, eliminating the need for revision surgeries. Moreover, the analysis of mobile cone-beam computed tomography images may help to elucidate the mechanisms of electrode tip fold-over.

Slim Modiolar Electrode Placement in Candidates for Electroacoustic Stimulation

OBJECTIVES

To determine rates of hearing preservation and performance in patients who met candidacy for electroacoustic stimulation (EAS) and were implanted with a slim modiolar electrode (CI532 or CI632).

DESIGN

Adult patients meeting Food and Drug Administration criteria for electroacoustic stimulation (preoperative low-frequency pure-tone average [LFPTA] less than 60 dB at 125, 250, and 500 Hz and monosyllabic word scores between 10% and 60% in the ear to be implanted), who received a slim modiolar electrode were included. Main outcome measures included rates of hearing preservation, defined as a LFPTA ≤80 dB at 125, 250, and 500 Hz, as well as postoperative low-frequency pure-tone threshold shifts, consonant-Nucleus-Consonant (CNC) word scores and AzBio sentences in noise scores.

RESULTS

Forty-six patients met inclusion criteria during a 4-year period. Mean (standard deviation) preoperative LFPTA was 34.5 (13.0) dB, and 71.7% had preserved hearing at initial activation. The mean LFPTA shift in patients who preserved hearing at initial activation was 19.7 (14.6) dB, compared with 62.6 (17.7) dB in patients who did not preserve hearing as per our definition. Perioperative steroid use was not different in patients with and without preserved hearing (X 2 (1, N = 46) = 0.19, p = .67, V = 0.06). One year after surgery, 57% of patients had a decline in LFPTA >80 dB and were no longer considered candidates for EAS, with 34.7% still retaining low-frequency thresholds ≤80 dB. CNC word scores at 1 year were 69.9% and 61.4% among individuals with and without preserved low-frequency hearing respectively, measured in their CI ear alone, in their regular listening condition of EAS or electric only ( t (32) = 1.13, p = 0.27, d = 0.39, 95% CI = -6.51, 22.86). Device use time did not differ between groups. Among adults with preserved residual hearing at 1 year (n = 16), 44% used EAS, although there was no significant difference in performance between EAS users and nonusers with preserved hearing. Loss of residual hearing over time did not result in a decline in speech perception performance.

CONCLUSION

The present study demonstrated favorable early rates of hearing preservation with a slim modiolar array. Performance was not significantly different in individuals with and without preserved low-frequency acoustic hearing, independent of EAS use. Compared with reports of short electrode use, the loss of residual hearing in patients implanted with this array did not impact speech perception performance.

An optically-guided cochlear implant sheath for real-time monitoring of electrode insertion into the human cochlea

In cochlear implant surgery, insertion of perimodiolar electrode arrays into the scala tympani can be complicated by trauma or even accidental translocation of the electrode array within the cochlea. In patients with partial hearing loss, cochlear trauma can not only negatively affect implant performance, but also reduce residual hearing function. These events have been related to suboptimal positioning of the cochlear implant electrode array with respect to critical cochlear walls of the scala tympani (modiolar wall, osseous spiral lamina and basilar membrane). Currently, the position of the electrode array in relation to these walls cannot be assessed during the insertion and the surgeon depends on tactile feedback, which is unreliable and often comes too late. This study presents an image-guided cochlear implant device with an integrated, fiber-optic imaging probe that provides real-time feedback using optical coherence tomography during insertion into the human cochlea. This novel device enables the surgeon to accurately detect and identify the cochlear walls ahead and to adjust the insertion trajectory, avoiding collision and trauma. The functionality of this prototype has been demonstrated in a series of insertion experiments, conducted by experienced cochlear implant surgeons on fresh-frozen human cadaveric cochleae.

Orientation of the Cochlea From a Surgeon's Perspective

Background

One of the mechanisms that cause tip fold-over is a misalignment between the electrode array's coiling direction and the cochlea's curving direction.

Objectives

We reviewed surgical videos and computed tomography (CT) datasets of the patients who underwent cochlear implantation procedures from January 2010 to December 2021, paying particular attention to the cochlea's orientation in the surgeon's microscopic view.

Methods

CT dataset and video recordings were analyzed to measure the "slope angle," which is the angle between the cochlea's coiling plane and the horizontal plane.

Results

There were 220 cases that met the criteria and completed the analysis. The mean slope angle was 12.1° ± 9.5°, with a minimum of -9.4° and maximum of 44.6°. However, each surgeon had a favored slope angle range.

Conclusion

Understanding the slope angle and making an effort to reduce the chance of misalignment during electrode insertion may help prevent tip fold-over of slim perimodiolar electrode arrays.

National study of hearing preservation rates and outcomes after cochlear implantation in Ireland

OBJECTIVE

To study the rate of hearing preservation and outcomes of hearing preservation candidates in a national cochlear implant centre. The HEARRING criteria was used.

METHODS

All cochlear implant candidates with preserved low frequency pure tone average (PTA) were included. All patients underwent cochlear implantation using a standard 'soft-surgery' technique. PTA was assessed at switch-on, 3, 6, 9 and 12 months postoperatively. The primary outcome was hearing preservation at 12 months.

RESULTS

Sixty six patients were included in the study between 2015 and 2020. Seventy one ears were implanted including 33 adults and 33 children with 5 bilateral implantations. Mean preoperative PTA was 74.8 dB (range 52.3-92 dB), mean postoperative PTA was 95.3 dB corresponding to a mean shift of 20.5 dB. In the adult population, HP rates were as follows: complete HP in 13%, partial HP in 39.1%, minimal HP in 30.4%, loss of hearing in 17.4%. In the paediatric population: complete HP in 20.7%, partial HP in 51.7%, minimal HP in 13.8% and loss of hearing in 13.8%. After the initial postoperative shift, there was no significant worsening of residual hearing during follow-up between 3 and 12 months. There were no significant prognostic factors for hearing preservation.

CONCLUSION

Hearing preservation rates using the HEARRING criteria are described. This study will help counselling and decision making in patients eligible for cochlear implantation with hearing preservation. Further studies are required to assess the performances and outcomes of electronatural and electroacoustic stimulation.

Early Hearing Preservation Outcomes Following Cochlear Implantation With New Slim Lateral Wall Electrode Using Electrocochleography

OBJECTIVE

Describe early hearing preservation (HP) cochlear implantation (CI) outcomes using a new slim lateral wall electrode (SLWE).

STUDY DESIGN

Prospective cohort study.

SETTING

Tertiary referral center.

PATIENTS

Adult CI candidates with preoperative low-frequency pure-tone average (LFPTA; 125, 250, 500 Hz) ≤60 dB HL.

INTERVENTION

CI with and without intracochlear real-time electrocochleography (RT-ECochG).

MAIN OUTCOME MEASURE

HP (LFPTA ≤80 dB HL), LFPTA shift, speech-perception performance measures, postoperative CT reconstruction.

RESULTS

Forty-two subjects were implanted with the SLWE. Thirty patients underwent full insertion without RT-ECochG feedback, and HP was maintained at 3-months postactivation for 7 (23.3%) patients with mean LFPTA shift of 57.5 ± 25.6 dB HL. RT-ECochG feedback was utilized on 12 patients, of whom 6 patients had full insertions and 6 patients had anywhere from 1 to 3 electrodes left outside of the cochlea based on RT-ECochG feedback. At 3 months postoperatively, HP was achieved on 10 (83.3%) patients and mean LFPTA shift was 18.9 c 11.7 dB HL. Mean difference between LFPTA threshold shift at 3-months postactivation with and without RT-ECochG was 38.6 dB HL (95% CI, 25.6-51.67). There was an improvement in delta CNC from preoperative to 3-months postactivation when using RT-ECochG, with mean difference 20.7% (95% CI, 3.3-38.1).

CONCLUSIONS

Use of RT-ECochG monitoring during SLWE placement results in fewer full electrode insertions and significantly better HP rates and speech-perception outcomes when compared with unmonitored insertions. Further investigation is needed to evaluate long-term audiologic outcomes to better understand the relationships among ECochG, cochlear trauma, functional outcomes, and HP.

Molecular aetiology of ski-slope hearing loss and audiological course of cochlear implantees

PURPOSE

A challenge for patients with ski-slope hearing loss is that hearing aids do not adequately amplify the mid-to-high frequencies necessary for speech perception and conversely, cochlear implant (CI) may damage low-frequency hearing. We aimed to describe the clinical profile of patients with ski-slope hearing loss, with a special focus on aetiology of such hearing loss and audiological course of low-frequency hearing after CI.

METHODS

We recruited hearing-impaired patients who visited a tertiary referral centre and met the criteria for ski-slope hearing loss patients from 2015 to 2021. Genetic testing was performed in all ski-slope hearing loss patients unless refused. Baseline audiograms of patients who continued to use hearing aids or who finally underwent CIs were reviewed. As for CI patients, outcome and hearing preservation rate were rigorously analysed.

RESULTS

Of 46 recruited patients with ski-slope hearing loss, 45 agreed to undergo genetic testing and causative variants were identified in 17 (37.8%) patients. The TMC1, MYO7A, and TMPRSS3 variants were the most common, while LRTOMT was newly identified as a causative gene. Twenty-five patients eventually received CI, while 13 continued to wear the hearing aid and 8 patients did not ever try hearing aids. CI in ski-slope hearing loss led to immediate and sufficient improvement of sentence recognition by as early as 3 months, however, the duration of hearing loss was inversely correlated with the sentence recognition score. The average hearing preservation rate (using the HEARRING classification) after CI was 53.0% (SD 30.0) and 45.6% (SD 31.1) at 1 year. Seventy-nine percent of implantees maintained functional low-frequency hearing (better than 85 dB at 250 and 500 Hz) eligible for electric-acoustic stimulation (EAS). A trend was found that patients with hair cell stereocilia-associated genetic variants may have a slightly better preservation, albeit with no statistical significance.

CONCLUSION

Detection rate of a molecular genetic aetiology of ski-slope hearing loss appears to be lower than other type of hearing loss reported in the literature. Especially with short hearing loss duration, CI in ski-slope hearing loss leads to immediate and sufficient speech improvement, while preserving functional low-frequency hearing eligible for EAS as many as in 79%. A certain genetic aetiology might be associated with a trend towards better low-frequency hearing preservation.

Electrocochleography and cognition are important predictors of speech perception outcomes in noise for cochlear implant recipients

Although significant progress has been made in understanding outcomes following cochlear implantation, predicting performance remains a challenge. Duration of hearing loss, age at implantation, and electrode positioning within the cochlea together explain ~ 25% of the variability in speech-perception scores in quiet using the cochlear implant (CI). Electrocochleography (ECochG) responses, prior to implantation, account for 47% of the variance in the same speech-perception measures. No study to date has explored CI performance in noise, a more realistic measure of natural listening. This study aimed to (1) validate ECochG total response (ECochG-TR) as a predictor of performance in quiet and (2) evaluate whether ECochG-TR explained variability in noise performance. Thirty-five adult CI recipients were enrolled with outcomes assessed at 3-months post-implantation. The results confirm previous studies showing a strong correlation of ECochG-TR with speech-perception in quiet (r = 0.77). ECochG-TR independently explained 34% of the variability in noise performance. Multivariate modeling using ECochG-TR and Montreal Cognitive Assessment (MoCA) scores explained 60% of the variability in speech-perception in noise. Thus, ECochG-TR, a measure of the cochlear substrate prior to implantation, is necessary but not sufficient for explaining performance in noise. Rather, a cognitive measure is also needed to improve prediction of noise performance.

Is Characteristic Frequency Limiting Real-Time Electrocochleography During Cochlear Implantation?

Objectives

Electrocochleography (ECochG) recordings during cochlear implantation have shown promise in estimating the impact on residual hearing. The purpose of the study was (1) to determine whether a 250-Hz stimulus is superior to 500-Hz in detecting residual hearing decrement and if so; (2) to evaluate whether crossing the 500-Hz tonotopic, characteristic frequency (CF) place partly explains the problems experienced using 500-Hz.

Design

Multifrequency ECochG comprising an alternating, interleaved acoustic complex of 250- and 500-Hz stimuli was used to elicit cochlear microphonics (CMs) during insertion. The largest ECochG drops (≥30% reduction in CM) were identified. After insertion, ECochG responses were measured using the individual electrodes along the array for both 250- and 500-Hz stimuli. Univariate regression was used to predict whether 250- or 500-Hz CM drops explained low-frequency pure tone average (LFPTA; 125-, 250-, and 500-Hz) shift at 1-month post-activation. Postoperative CT scans were performed to evaluate cochlear size and angular insertion depth.

Results

For perimodiolar insertions (N = 34), there was a stronger linear correlation between the largest ECochG drop using 250-Hz stimulus and LFPTA shift (r = 0.58), compared to 500-Hz (r = 0.31). The 250- and 500-Hz CM insertion tracings showed an amplitude peak at two different locations, with the 500-Hz peak occurring earlier in most cases than the 250-Hz peak, consistent with tonotopicity. When using the entire array for recordings after insertion, a maximum 500-Hz response was observed 2-6 electrodes basal to the most-apical electrode in 20 cases (58.9%). For insertions where the apical insertion angle is >350 degrees and the cochlear diameter is <9.5 mm, the maximum 500-Hz ECochG response may occur at the non-apical most electrode. For lateral wall insertions (N = 14), the maximum 250- and 500-Hz CM response occurred at the most-apical electrode in all but one case.

Conclusion

Using 250-Hz stimulus for ECochG feedback during implantation is more predictive of hearing preservation than 500-Hz. This is due to the electrode passing the 500-Hz CF during insertion which may be misidentified as intracochlear trauma; this is particularly important in subjects with smaller cochlear diameters and deeper insertions. Multifrequency ECochG can be used to differentiate between trauma and advancement of the apical electrode beyond the CF.

Tight modiolar proximity and feasibility of slim modiolar cochlear implant electrode array insertion in diverse etiologies of hearing loss

PURPOSE

To report on our experience with the slim modiolar electrode (SME) especially focusing on the wide range of etiologies including inner ear anomalies, tumors, ossifications, and even revision surgeries.

METHODS

All the cochlear implantation cases performed from June 2018 to September 2019 by a single surgeon was prospectively recruited. The molecular/radiological etiology of hearing loss, intraoperative outcomes, and radiographic studies of cases where the SME was implanted was reviewed to evaluate compatibility of SME for the wide range of etiologies. For cases where SME replaced the other electrode as a revision, audiologic assessment was also made.

RESULTS

Among the 99 ears implanted during the study period, the SME was successfully implanted in 86 ears. These SME cases comprised inner ear anomaly/cochear nerve deficiency (n = 21) including cochlear hypoplasia type IV with the modiolus, intracochlear schwannoma (n = 1), far advanced otosclerosis (n = 1) and 7 revision cases. The SME was successfully used in 7 revision surgeries to replace the existing electrode. Shorter spiral diameter and decreased intracochlear position index for SME was found compared with their previous electrodes. Four out of the 6 patients who received revision implantation showed better speech perception after their surgeries.

CONCLUSION

The SME can be implanted in any cases unless the integrity of the modiolus is totally compromised. Due to its slim design and tight modiolar-hugging feature, good functional outcome can also be anticipated. Additionally, it is suitable for revision surgeries possibly allowing better hearing outcomes which may be attributed to its closer proximity to the modiolus.