Does pediatric cochlear implant insertion technique affect intraoperative neural response telemetry thresholds?

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 Neural Response Telemetry and Auditory Outcomes in Pediatric Cochlear Implantation

OBJECTIVE

To evaluate the relationship between intraoperative neural response telemetry (NRT) and postoperative auditory testing outcomes in children.

STUDY DESIGN

Retrospective study.

SETTING

Tertiary-care academic center.

METHODS

Children who underwent cochlear implantation using the Cochlear Corporation device between 2010 and 2019 were included. Associations of average NRT and the slope of amplitude with postoperative auditory outcomes including functional auditory measure Infant-Toddler Meaningful Auditory Integration Scale (IT-MAIS), and speech perception testing (consonant-nucleus-consonant [CNC], Pediatric AzBio [BABY BIO], Hearing In Noise Test [HINT], and Northwestern University Children's Perception of Speech [NU-CHIPS]), measured between 6 and 57 months after implantation, were assessed using Spearman's rank correlation (ρ).

RESULTS

Thirty-eight patients (19 female, 19 male) and 54 ears were included. The median age of implantation was 20.6 months (range 9.6 months to 10.6 years). Eight (21%) children had neurologic disorders such as stroke, epilepsy, cerebral palsy, and other causes. Thirteen (34%) children had connexin mutations. Average NRT was not significantly correlated with postoperative auditory outcomes (IT-MAIS [ρ = -0.08, p = .74], CNC [ρ = 0.19, p = .32], BABY BIO [ρ = 0.21, p = .29], HINT [ρ = 0.05, p = .83]) and NU-CHIPS (ρ = 0.21, p = .28). The average slopes of amplitude and comfort level were not strongly correlated with any auditory outcomes (p > .05).

CONCLUSIONS

Intraoperative NRT was not correlated with any postoperative functional auditory outcomes. Patient counseling should include discussions that a subpar intraoperative cochlear response does not preclude favorable speech and auditory outcomes.

Clinical significance of the neural response telemetric thresholds in Mandarin-speaking cochlear implant patients

BACKGROUND

It is unclear whether neural response telemetric (NRT) thresholds are related to lexical tonal language performance after cochlear implants (CIs). We explored the factors associated with changes in NRT thresholds and postoperative performance of CI patients.

METHODS

Patients receiving nucleus 24 CIs in our hospital from November 2010 were enrolled. We analyzed medical records and NRT thresholds. Mandarin speech and tone identification were measured in CI patients for at least 1 year postoperatively.

RESULTS

Seventy-two patients with an average age of 16.1 years received CIs. The postoperative NRT threshold was lower than the intraoperative threshold. The NRT threshold was higher in the early- than the late-activation group (mapping within 21 vs >21 days postoperatively, respectively). Lower intraoperative NRT thresholds and curved electrodes were significantly associated with lower postoperative NRT thresholds. In multiple linear regression analysis, only postoperative NRT thresholds significantly affected speech and tone perception, including word recognition scores, tone perception, and comprehension of easy and difficult sentences (all p < 0.05). Other clinical parameters, including age, gender, implant type, and activation timing, were not significantly associated with clinical tone or speech outcomes.

CONCLUSION

Curved electrode arrays were associated with lower postoperative NRT thresholds. A lower postoperative NRT threshold might predict better performance of Mandarin-speaking CI patients. Future studies should evaluate factors that affect both postoperative NRT thresholds and lexical tonal language performance.

Comparison of Perimodiolar Electrodes: Imaging and Electrophysiological Outcomes

BACKGROUND

The perimodiolar CI532 Slim Modiolar electrode has been designed to bring the electrode contacts close to auditory nerve while reducing cochlear trauma during its insertion. It is currently unknown to what extent the electrode position and electrophysiological outcomes of the Slim Modiolar electrode differ from other perimodiolar electrodes.

OBJECTIVES

The objective was to compare the electrode position and electrophysiological outcomes between the CI532 Slim Modiolar and CI512 Contour Advance electrode.

METHOD

Forty-six adult patients received a Slim Modiolar or Contour Advance electrode. Electrode types were compared using intraoperative electrode impedances, evoked compound action potential (ECAP) and stapedius reflex thresholds, as well as position parameters from postoperative computed tomography or digital volume tomography images (medial-lateral position, electrode-to-modiolus distance, insertion angle).

RESULTS

The medial-lateral position indicates a closer modiolar placement of the Slim Modiolar compared with the Contour Advance. Individual electrode contact measurements, however, showed significantly larger electrode-to-modiolus distances and higher ECAP thresholds for the Slim Modiolar in the basal region. On contacts E20-22 the Slim Modiolar is slightly closer to the modiolus compared with the Contour Advance, but this did not result in lower ECAP thresholds.

CONCLUSIONS

Perimodiolar electrodes can vary in their intracochlear position, leading to divergent electrophysiological outcomes. To detect these differences, investigations must be done for each electrode contact rather than using a global factor for the whole electrode array. While the electrode dislocation rate is lower with the Slim Modiolar than with the Contour Advance, electrode-to-modiolus proximity is smaller and ECAP thresholds are lower with the Contour Advance in the basal cochlear region.

Impact of cochlear tonotopy on electrically evoked compound action potentials (ECAPs)

BACKGROUND

A wide range of cochlear implant electrode designs exists. Lateral wall electrodes may be favored for their potential to preserve residual hearing by virtue of being thin and delicate; whereas perimodiolar electrodes may have advantages in case of profound hearing loss, due to electrode positioning in close proximity to the auditory nerve fibers.

AIM

The aim of this study was to investigate the impact of these two array designs on the interaction between electrodes and the auditory nerve in different tonotopic regions of the cochlea.

PATIENTS AND METHODS

A retrospective study of both adult and pediatric cochlear implant recipients (CI24RE/CI512 or CI422, Cochlear®) was undertaken. The differences of threshold Neural Response Telemetry (tNRT) acquired 12 months after surgery were analyzed with respect to the tonotopic location.

RESULTS

The results of 168 implants showed that perimodiolar arrays had lowest thresholds in the basal region whereas straight arrays had lowest thresholds in the apex. Highest thresholds for both array types were encountered in the medial parts.

CONCLUSIONS AND SIGNIFICANCE

tNRTs differ depending on electrode type and location inside the cochlea. This should be considered pre implantation when choosing the electrode array type and post-implantation when mapping the CI program.