Cochlear coverage with lateral wall cochlear implant electrode arrays affects post-operative speech recognition

Investigation of Automated Cochlear Length and Cochlear Implant Insertion Angle Predictions with a Surgical Planning Platform

INTRODUCTION

Preoperative anatomical assessment is essential to optimize the outcome of individualized cochlear implantation. Algorithms based on cochlear diameters simplify this evaluation. The new version of a surgical planning platform is capable of performing this determination automatically. Our study evaluated the robustness of automated measurements and compared individual differences between automated and manual measurements, including predicting cochlear duct length and insertion angles.

MATERIALS AND METHODS

The preoperative cone beam CT scans of 55 MED-EL cochlear implant patients were analyzed. Using the surgical planning platform, the anatomical diameters were measured automatically and manually. The values were compared, as well as the predictions of the insertion angles and prediction of cochlear duct length.

RESULTS

The analyses showed good agreement between manual and automatic measurements of cochlear diameters, with the exception of cochlear height, where a significant difference was observed. Some discrepancies were noted for the prediction of the cochlear length duct without, however, a significant impact. Predictions of insertion angles based on automated measurements were comparable to the postoperative evaluations, with no significant difference from the manual ones.

DISCUSSION

The robustness of automated assessments is essential for integration into clinical practice. Automated measurements of cochlear dimensions are comparable to manual ones. However, image quality and the presence of anatomical abnormalities may influence the results. In this study, the evaluation of the insertion angle prediction was strengthened by comparison with postoperative results taking into account the actual insertion depth.

Scala Tympani Volume Influences Initial 6-Month Hearing Preservation With Lateral Wall Electrode Arrays

OBJECTIVES

To examine the effects of scala tympani (ST) volume, cochlear duct length (CDL), and angular insertion depth (AID) on low-frequency hearing preservation for cochlear implant (CI) recipients of lateral wall electrode arrays.

METHODS

A retrospective review identified 45 adult CI recipients of 24-, 28-, or 31.5-mm lateral wall electrode arrays with preoperative unaided hearing thresholds ≤45 decibel hearing level (dB HL) at 250 Hz. All patients underwent preoperative and postoperative computed tomography to evaluate cochlear morphology and electrode array position. A linear mixed effects model evaluated effects of ST volume, CDL, AID, preoperative low-frequency pure-tone average (LFPTA; 125, 250, and 500 Hz), age at surgery, and biological sex on the postoperative change in LFPTA at activation and 6 months post-activation.

RESULTS

There were significant main effects of ST volume (p = 0.044), age (p = 0.028), and biological sex (p = 0.003), indicating better low-frequency hearing preservation for CI recipients with larger ST volumes, younger age at surgery, and female biological sex. Although CDL positively correlated with ST volume (r = 0.74, p < 0.001), there was no significant main effect of CDL (p = 0.367). A broad range in AID of the most apical electrode contact was observed (301.4°-681.8°); however, there was no significant main effect of AID on low-frequency hearing preservation (p = 0.700).

CONCLUSIONS

During the initial 6 months following implantation, intrinsic factors such as cochlear morphology may have a greater impact on low-frequency hearing preservation than apical positioning of a flexible lateral wall electrode array when using soft surgical techniques.

LEVEL OF EVIDENCE

3 Laryngoscope, 135:1781-1787, 2025.

Influence of cochlear coverage on speech perception in single sided deafness, bimodal, and bilateral implanted cochlear implant patients

PURPOSE

Individualized cochlear implantation (CI) is essential to facilitate optimal hearing results for patients. Influence of cochlear coverage (CC) has been studied, however without consideration of different CI-categories, like single sided deafness (SSD), bimodal, and bilateral separately.

METHODS

Retrospective analysis of preoperative CT scans was performed at a tertiary center. For each patient their individual CC with the selected electrode array was calculated off the complete CDL. Patients were categorized into SSD (n = 30), bimodal (n = 72), and bilateral CI patients (n = 29). Speech perception within the first 12 months post-implantation was compared between patient groups with shorter and longer CC. For subgroup analysis the cutoff between a shorter or longer CC was identified by the median.

RESULTS

Cutoff between a shorter or longer CC was identified at 65% off the complete CDL for SSD and bimodal patients, and at 70% for bilateral patients. In SSD-patients longer CC was associated with better performance at activation (CCshorter 20.0 ± 28.9% vs. CClonger 31.5 ± 24.7%; p = 0.04) and no benefit was found with deeper insertion at 12 months. No significant benefit was found for deeper insertion in bimodal and bilateral patients.

CONCLUSIONS

Capacities of hearing performance seem to differ between SSD, bimodal and bilateral patients within the first year after implantation with regards to cochlear coverage. SSD-patients appear to benefit from deeper insertion than 65% up to 12 months after implantation. However, these results should be interpreted with caution, hence development of speech perception with CI is influenced by a whole range of factors, and bimodal and bilateral treated patients are extremely heterogenous patient groups.

Effects of Insertion Depth and Modiolar Proximity on Cochlear Implant Speech Recognition Outcomes With a Precurved Electrode Array

OBJECTIVES

To examine the relationship between angular insertion depth (AID), modiolar proximity, and speech recognition outcomes for cochlear implant (CI) recipients of a precurved electrode array.

STUDY DESIGN

Retrospective review.

SETTING

Tertiary academic referral center.

PATIENTS

Thirty-five adult CI recipients (n = 40 ears) of precurved electrode arrays listening with a CI-alone device.

INTERVENTIONS

Cochlear implantation with postoperative computed tomography.

MAIN OUTCOME MEASURES

Consonant-nucleus-consonant (CNC) word recognition at 6 months post-activation.

RESULTS

A multivariate regression model demonstrated that both deeper apical AID and closer modiolar proximity in the basal turn were independently associated with better CNC word scores at 6 months (F2,37 = 7.264, p = 0.002). A deeper basal insertion depth was positively correlated with apical AID (r = 0.754, p < 0.001) but negatively correlated with modiolar proximity in the basal turn (r = -0.766, p < 0.001).

CONCLUSIONS

These data suggest that both apical cochlear coverage and modiolar proximity independently confer speech recognition benefit with a precurved array. However, these benefits are mutually exclusive for current precurved array designs as a deeper basal insertion depth results in greater apical coverage but lateralization of electrodes away from the modiolus in the basal turn. Future work is needed to elucidate mechanisms behind these findings that may motivate electrode array design modifications to further optimize outcomes for CI users.

A Level-Adjusted Cochlear Frequency-to-Place Map for Estimating Tonotopic Frequency Mismatch With a Cochlear Implant

OBJECTIVES

To provide a level-adjusted correction to the current standard relating anatomical cochlear place to characteristic frequency (CF) in humans, and to re-evaluate anatomical frequency mismatch in cochlear implant (CI recipients considering this correction. It is proposed that a level-adjusted place-frequency function may represent a more relevant tonotopic benchmark for CIs in comparison to the current standard.

DESIGN

The present analytical study compiled data from 15 previous animal studies that reported isointensity responses from cochlear structures at different stimulation levels. Extracted outcome measures were CFs and centroid-based best frequencies at 70 dB SPL input from 47 specimens spanning a broad range of cochlear locations. A simple relationship was used to transform these measures to human estimates of characteristic and best frequencies, and nonlinear regression was applied to these estimates to determine how the standard human place-frequency function should be adjusted to reflect best frequency rather than CF. The proposed level-adjusted correction was then compared with average place-frequency positions of commonly used CI devices when programmed with clinical settings.

RESULTS

The present study showed that the best frequency at 70 dB SPL (BF70) tends to shift away from CF. The amount of shift was statistically significant (signed-rank test z = 5.143, p < 0.001), but the amount and direction of shift depended on cochlear location. At cochlear locations up to 600° from the base, BF70 shifted downward in frequency relative to CF by about 4 semitones on average. Beyond 600° from the base, BF70 shifted upward in frequency relative to CF by about 6 semitones on average. In terms of spread (90% prediction interval), the amount of shift between CF and BF70 varied from relatively no shift to nearly an octave of shift. With the new level-adjusted place-frequency function, the amount of anatomical frequency mismatch for devices programmed with standard-of-care settings is less extreme than originally thought and may be nonexistent for all but the most apical electrodes.

CONCLUSIONS

The present study validates the current standard for relating cochlear place to CF, and introduces a level-adjusted correction for how best frequency shifts away from CF at moderately loud stimulation levels. This correction may represent a more relevant tonotopic reference for CIs. To the extent that it does, its implementation may potentially enhance perceptual accommodation and speech understanding in CI users, thereby improving CI outcomes and contributing to advancements in the programming and clinical management of CIs.

A level adjusted cochlear frequency-to-place map for estimating tonotopic frequency mismatch with a cochlear implant

Objectives

To provide a level-adjusted correction to the current standard relating anatomical cochlear place to characteristic frequency in humans, and to re-evaluate anatomical frequency mismatch in cochlear implant (CI) recipients considering this correction. It is hypothesized that a level-adjusted place-frequency function may represent a more accurate tonotopic benchmark for CIs in comparison to the current standard.

Design

The present analytical study compiled data from fifteen previous animal studies that reported iso-intensity responses from cochlear structures at different stimulation levels. Extracted outcome measures were characteristic frequencies and centroid-based best frequencies at 70 dB SPL input from 47 specimens spanning a broad range of cochlear locations. A simple relationship was used to transform these measures to human estimates of characteristic and best frequencies, and non-linear regression was applied to these estimates to determine how the standard human place-frequency function should be adjusted to reflect best frequency rather than characteristic frequency. The proposed level-adjusted correction was then compared to average place-frequency positions of commonly used CI devices when programmed with clinical settings.

Results

The present study showed that the best frequency at 70 dB SPL (BF70) tends to shift away from characteristic frequency (CF). The amount of shift was statistically significant (signed-rank test z = 5.143, p < 0.001), but the amount and direction of shift depended on cochlear location. At cochlear locations up to 600° from the base, BF70 shifted downwards in frequency relative to CF by about 4 semitones on average. Beyond 600° from the base, BF70 shifted upwards in frequency relative to CF by about 6 semitones on average. In terms of spread (90% prediction interval), the amount of shift between CF and BF70 varied from relatively no shift to nearly an octave of shift. With the new level-adjusted frequency-place function, the amount of anatomical frequency mismatch for devices programmed with standard of care settings is less extreme than originally thought, and may be nonexistent for all but the most apical electrodes.

Conclusions

The present study validates the current standard for relating cochlear place to characteristic frequency, and introduces a level-adjusted correction for how best frequency shifts away from characteristic frequency at moderately loud stimulation levels. This correction may represent a more accurate tonotopic reference for CIs. To the extent that it does, its implementation may potentially enhance perceptual accommodation and speech understanding in CI users, thereby improving CI outcomes and contributing to advancements in the programming and clinical management of CIs.

Comparison of 96-kV and 120-kV cone-beam CT for the assessment of cochlear implants

BACKGROUND

To compare the diagnostic value of 120-kV with conventional 96-kV Cone-Beam CT (CBCT) of the temporal bone after cochlear implant (CI) surgery.

METHODS

This retrospective study included CBCT scans after CI surgery between 06/17 and 01/18. CBCT allowed examinations with 96-kV or 120-kV; other parameters were the same. Two radiologists independently evaluated following criteria on 5-point Likert scales: osseous spiral lamina, inner and outer cochlear wall, semi-circular canals, mastoid trabecular structure, overall image quality, metal and motion artefacts, depiction of intracochlear electrode position and visualisation of single electrode contacts. Effective radiation dose was assessed.

RESULTS

Seventy-five patients (females, n = 39 [52.0%], mean age, 55.8 ± 16.5 years) were scanned with 96-kV (n = 32, 42.7%) and 120-kV (n = 43, 57.3%) protocols including CI models from three vendors (vendor A n = 7; vendor B n = 43; vendor C n = 25). Overall image quality, depiction of anatomical structures, and electrode position were rated significantly better in 120-kV images compared to 96-kV (all p < = 0.018). Anatomical structures and electrode position were rated significantly better in 120-kV CBCT for CI models from vendor A and C, while 120-kV did not provide improved image quality in CI models from vendor B. Radiation doses were significantly higher for 120-kV scans compared to 96-kV (0.15 vs. 0.08 mSv, p < 0.001).

CONCLUSIONS

120-kV and 96-kV CBCT provide good diagnostic images for the postoperative CI evaluation. While 120-kV showed improved depiction of temporal bone and CI electrode position compared to 96-kV in most CI models, the 120-kV protocol should be chosen wisely due to a substantially higher radiation exposure.

Morphologic Analysis of the Scala Tympani Using Synchrotron: Implications for Cochlear Implantation

OBJECTIVES

To use synchrotron radiation phase-contrast imaging (SR-PCI) to visualize and measure the morphology of the entire cochlear scala tympani (ST) and assess cochlear implant (CI) electrode trajectories.

METHODS

SR-PCI images were used to obtain geometric measurements of the cochlear scalar diameter and area at 5-degree increments in 35 unimplanted and three implanted fixed human cadaveric cochleae.

RESULTS

The cross-sectional diameter and area of the cochlea were found to decrease from the base to the apex. This study represents a wide variability in cochlear morphology and suggests that even in the smallest cochlea, the ST can accommodate a 0.4 mm diameter electrode up to 720°. Additionally, all lateral wall array trajectories were within the anatomically accommodating insertion zone.

CONCLUSION

This is the first study to use SR-PCI to visualize and quantify the entire ST morphology, from the round window to the apical tip, and assess the post-operative trajectory of electrodes. These high-resolution anatomical measurements can be used to inform the angular insertion depth that can be accommodated in CI patients, accounting for anatomical variability.

LEVEL OF EVIDENCE

N/A. Laryngoscope, 134:2889-2897, 2024.

Optimization of pharmacological interventions in the guinea pig animal model-a new approach to calculate the perilymph volume of the scala tympani

Objective

The guinea pig serves as a well-established animal model for inner ear research, offering valuable insights into the anatomy, physiology, and therapeutic interventions of the auditory system. However, the heterogeneity of results observed in both in-vivo experiments and clinical studies poses challenges in understanding and optimizing pharmacotherapy outcomes. This heterogeneity may be due to individual differences in the size of the guinea pig cochlea and thus in the volume of the scala tympani (ST), which can lead to different drug concentrations in the ST, a fact that has been largely overlooked thus far. To address this issue, we aimed to develop an approach for calculating the individual volume of perilymph within the ST before and after cochlear implant insertion.

Method

In this study, high-resolution μCT images of a total of n = 42 guinea pig temporal bones were used to determine the volume of the ST. We compared fresh, frozen, and fixed tissues from both colored and albino strains to evaluate the potential influence of tissue condition and strain on the results.

Results

Our findings demonstrate a variability in mean ST volume with a relative standard deviation (RSD) of 14.7%, comparable to studies conducted with humans (range RSD: 5 to 20%). This indicates that the guinea pig cochlea exhibits similar variability to that of the human cochlea. Consequently, it is crucial to consider this variability when designing and conducting studies utilizing the guinea pig as an animal model. Furthermore, we successfully developed a tool capable of estimating ST volume without the need for manual segmentation, employing two geometric parameters, basal diameter (A) and width (B) of the cochlea, corresponding to the cochlear footprint. The tool is available for free download and use on our website.

Conclusion

This novel approach provides researchers with a valuable tool to calculate individual ST volume in guinea pigs, enabling more precise dosing strategies and optimization of drug concentrations for pharmacotherapy studies. Moreover, our study underscores the importance of acknowledging and accounting for inter-individual variability in animal models to enhance the translational relevance and applicability of research outcomes in the field of inner ear investigations.