Electrophysiological measurements with electrode types of different perimodiolar properties and the same cochlear implant electronics - a retrospective comparison study

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Evaluation of CI electrode position from imaging: comparison of an automated technique with the established manual method

BACKGROUND

A manual evaluation of the CI electrode position from CT and DVT scans may be affected by diagnostic errors due to cognitive biases. The aim of this study was to compare the CI electrode localization using an automated method (image-guided cochlear implant programming, IGCIP) with the clinically established manual method.

METHODS

This prospective experimental study was conducted on a dataset comprising N=50 subjects undergoing cochlear implantation with a Nucleus® CI532 or CI632 Slim Modiolar electrode. Scalar localization, electrode-to-modiolar axis distances (EMD) and angular insertion depth (aDOI) were compared between the automated IGCIP tool and the manual method. Two raters made the manual measurements, and the interrater reliability (±1.96·SD) was determined as the reference for the method comparison. The method comparison was performed using a correlation analysis and a Bland-Altman analysis.

RESULTS

Concerning the scalar localization, all electrodes were localized both manually and automatically in the scala tympani. The interrater differences ranged between ±0.2 mm (EMD) and ±10° (aDOI). There was a bias between the automatic and manual method in measuring both localization parameters, which on the one hand was smaller than the interrater variations. On the other hand, this bias depended on the magnitude of the EMD respectively aDOI. A post-hoc analysis revealed that the deviations between the methods were likely due to a different selection of mid-modiolar axis.

CONCLUSIONS

The IGCIP is a promising tool for automated processing of CT and DVT scans and has useful functionality such as being able to segment the cochlear using post-operative scans. When measuring EMD, the IGCIP tool is superior to the manual method because the smallest possible distance to the axis is determined depending on the cochlear turn, whereas the manual method selects the helicotrema as the reference point rigidly. Functionality to deal with motion artifacts and measurements of aDOI according to the consensus approach are necessary, otherwise the IGCIP is not unrestrictedly ready for clinical use.

Intraoperative Electrically Evoked Compound Action Potential Growth and Maximum Amplitudes in Hearing Preservation Cochlear Implant Recipients

BACKGROUND

Electrically evoked compound action potentials (eCAPs) obtained from cochlear implant (CI) recipients reflect responsiveness of the auditory nerve to electrical stimulation. The recent use of atraumatic electrode arrays and expansion of CI candidacy to listeners with greater residual hearing may lead to increased clinical utility of intraoperative eCAP recordings.

OBJECTIVES

To examine the effect of electrode array (slim modiolar versus slim straight) on suprathreshold intraoperative eCAP recordings in hearing preservation CI recipients. A secondary goal was to examine potential clinical applications of intraoperative eCAPs for predicting immediate hearing preservation and speech perception outcomes.

METHODS

Retrospective study of 113 adult hearing preservation CI candidates implanted from 2015 to 2019 with either a slim modiolar or slim straight electrode array. Intraoperative eCAP growth functions and maximum amplitudes were obtained at several intracochlear electrodes and examined as a function of implanted array and hearing preservation status, while controlling for electrode impedance.

RESULTS

From basal to apical electrodes, progressively larger eCAP amplitudes and steeper slopes were recorded. Steeper eCAP slopes at apical electrodes were also seen for recipients of the slim modiolar array (versus slim straight). Suprathreshold eCAP responses did not differ as a function of hearing preservation and were not associated with speech recognition.

CONCLUSIONS

More robust eCAP responses were obtained from apical electrodes, which is consistent with better low-frequency thresholds in hearing preservation recipients. This effect was compounded by type of electrode array. Results also suggest that intraoperative, suprathreshold eCAPs cannot be used to predict the success of hearing preservation surgery or performance with the CI.

Electrically Evoked Auditory Late Responses as a Novel Method for Cochlear Implant Programming

HYPOTHESIS

Electrically evoked auditory late responses (eALR) are useful as an objective cochlear implant (CI) fitting method.

BACKGROUND

Different objective and behavioral methods are used for CI fitting. However, there is no objective method that indicates that the electrical signal reaches the auditory cortex. eALR is an indicator that electrical signals reach the auditory cortex, so our aim was to investigate the use of eALR as an objective method for CI programming.

METHODS

Two different programs were created for 21 unilateral Med-El CI users. In the first program, the most comfortable level (MCL) was adjusted with the electrical stapes reflex threshold (eSRT), and the threshold levels (THR) were behaviorally adjusted according to the user's feedback. In the second program, the MCL level was adjusted to a level where all the components of the eALR were clearly seen, and the user did not feel uncomfortable; the THR levels were adjusted to the lowest level where the eALR P1 wave could be seen. The results of the MCL and THR levels of the two programs and the free field tests conducted with both programs were compared.

RESULTS

While MCL levels did not differ significantly between the two programs, a significant difference was observed between THR levels. In addition, no significant difference was found between hearing and speech tests with CI in the free field.

CONCLUSION

The results revealed no significant performance difference between the two programs and that eALR could be preferred as an objective method for MCL determination.

A new method of preoperative assessment of correct electrode array alignment based on post-operative measurements in a cochlear implanted cohort

PURPOSE

During cochlear implantation surgery, a range of complications may occur such as tip fold-over. We recently developed a method to estimate the insertion orientation of the electrode array. The aim of the study was to determine the optimal angle of orientation in a cohort of cochlear implanted patients.

METHODS

On eighty-five CT scans (80 uncomplicated insertions and 5 cases with tip fold-over), location of the electrode array's Insertion Guide (IG), Orientation marker (OM) and two easily identifiable landmarks (the round window (RW) and the incus short process (ISP)) were manually marked. The angle enclosed by ISP-RW line and the Cochlear™ Slim Modiolar electrode array's OM line determined the electrode array insertion angle.

RESULTS

The average insertion angle was 45.0-47.2° ± 10.4-12° SD and was validated with 98% confidence interval. Based on the measurements obtained, patients' sex and age had no impact on the size of this angle. Although the angles of the tip fold-over cases (44.9°, 46.9°, 34.2°, 54.3°, 55.9°) fell within this average range, the further it diverted from the average it increased the likelihood for tip fold-over.

CONCLUSION

Electrode array insertion in the individually calculated angle relative to the visible incus short process provides a useful guide for the surgeon when aiming for the optimal angle, and potentially enhances good surgical outcomes. Our results show that factors other than the orientation angle may additionally contribute to failures in implantation when the Slim Modiolar electrode is used.

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.

Longitudinal outcomes of cochlear implantation and bimodal hearing in a large group of adults: A multicenter clinical study

OBJECTIVE

To evaluate speech understanding outcomes in a large adult cohort who demonstrated poor hearing performance with well fit hearing aids in the unilateral and bilateral or bimodal listening conditions at preimplant, 3-, 6- and 12-months.

SUBJECTS

Post-linguistically deafened adults (N = 100) with bilateral moderate-to-profound sensorineural hearing loss and limited functional benefit from well fit bilateral hearing aids.

METHOD

A multicenter, prospective, repeated-measures, within-subject controlled study was conducted. All subjects were implanted with a Slim Modiolar cochlear implant and were required to use bimodal stimulation (cochlear implant and hearing aid in contralateral ear) for 6-months postimplant and optionally to 12-months. Evaluations included: speech recognition for monosyllabic consonant-nucleus-consonant (CNC) words in quiet; AzBio sentences in coincident noise (at +5 and +10 dB signal-to-noise ratio (SNR)), in implant ear and bimodal conditions. All speech tests were performed at preimplant and 6-months postimplant for primary endpoint outcomes, and a subset of speech tests at 3- and 12-months.

RESULTS

In the implant ear only, at 3-, 6- and 12-months postimplant, 84%, 93% and 97% of subjects respectively, demonstrated significantly improved monosyllabic word scores in quiet compared to preimplant hearing aid scores (p < 0.05). At 12-months, a mean gain of 51% points, for monosyllabic words and 32% points for sentences in noise was observed (p < 0.001). In the bimodal condition, at 6-months postimplant, 87% of subjects demonstrated significantly improved monosyllabic word scores in quiet compared to preimplant bilateral hearing aid scores (p < 0.05). At 6-months, a mean gain of 40% points, for monosyllabic words was observed (p < 0.001). Speech scores for sentences in noise significantly improved for the bimodal condition at 6- and 12-months (p < 0.001). In addition to speech scores for the implanted ear, bimodal condition scores demonstrated further increments, especially for sentences in noise at 6- and 12-months (p < 0.001).

CONCLUSION

Results support that bimodal hearing is superior to bilateral hearing aids in this cohort of bilateral moderate-to-profound adult hearing aid users. Our study cohort demonstrated significant improvements for speech scores for the cochlear implant (CI) ear only and bimodal conditions compared to the baseline preimplant unilateral and bilateral hearing aid conditions respectively. The greatest gain in performance was in the first three months of device use with incremental improvement through 12 months. These findings indicate that when hearing aids fit to National Acoustics Laboratory (NAL-1) targets do not provide the necessary audibility needed for speech recognition, referral for CI-candidacy evaluation is strongly recommended.

TRIAL REGISTRATION

Clintrial.govNCT03007472. Registered 01/02/2017, https://clinicaltrials.gov/ct2/show/NCT03007472?term=clinical+evaluation+of+the+nucleus+CI532&draw=2&rank=2.

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.

Modiolar Proximity of Slim Modiolar Electrodes and Cochlear Duct Length: Correlation for Potential Basis of Customized Cochlear Implantation With Perimodiolar Electrodes

OBJECTIVES

Recent studies have shown that cochlear duct length (CDL) varies among individuals and could significantly influence the final position of the electrode and its trajectory in the cochlea. Given this, we hypothesized that the degree of modiolar proximity of novel slim modiolar electrodes, such as CI532 and CI632, can also be affected by CDL. To test this hypothesis, we retrospectively evaluated individual CDL to determine if there is any significant correlation of CDL with degree of modiolar proximity.

METHODS

Fifty-one ears from 38 subjects implanted with slim modiolar electrodes by a single surgeon through the round window approach using the pull-back technique were included. Our cohort was classified according to the deafness onset (congenital versus postlingual) and the degree of modiolar proximity (less versus tight) with reference to the spiral diameter made by the slim modiolar electrodes in situ on transorbital x ray. We then analyzed the CDL and its metrics using a readily available surgical preplanning tool (OTOPLAN) to obtain comparable data.

RESULTS

Among 30 ears associated with congenital deafness, 9 ears (30%) showed less modiolar proximity, while none of the 21 ears from 19 subjects with postlingual deafness exhibited "less modiolar proximity" based on our criteria. In this study, CDL showed significant variation among subjects. Importantly, a significant inverse correlation between spiral diameter and CDL (ρ = -0.581, p < 0.001) was found, showing that shorter CDLs have longer spiral diameter and less modiolar proximity. Moreover, further pull-back technique characterized by pulling out the electrode a little bit more in cases with shorter CDL, if not always, exhibited tighter modiolar proximity.

CONCLUSION

A preponderance of less modiolar proximity of the electrode was observed exclusively among congenital deafness cases, demonstrated by a less tight spiral configuration even under the pull-back technique. Our data suggest that shorter CDL is associated with a less tight spiral configuration of slim modiolar electrodes postoperatively. Depending on the insertion technique, the differential degree of modiolar proximity of slim modiolar electrodes can be alleviated in cases with short CDL, which justifies cochlear duct length-based customized insertion of slim modiolar electrodes.