Misplaced Cochlear Implant Electrodes Outside the Cochlea: A Literature Review and Presentation of Radiological and Electrophysiological Findings

The Role of Routine Plain Film Imaging Post Cochlear Implantation

OBJECTIVE

We aimed to evaluate the efficacy of routine post-op X-ray in cochlear implantation patients.

STUDY DESIGN

Retrospective chart review study.

SETTING

Primary or revision cochlear implant patients who had routine postoperative X-ray (XR) or had planned postoperative computed tomography (CT) due to clinical concerns for array malposition.

METHODS

All images were reviewed, and those were considered abnormal if there was a bent tip, kinking, incomplete insertion, or if the electrode array didn't follow the expected cochlear curvature. Postoperative CT scans were performed in patients with abnormal postoperation X-ray, or if there were abnormal surgical findings encountered during insertion which raised the suspicion for suboptimal placement.

RESULTS

A total of 195 patients with a mean age of 64.8 ± 18.9 years were included. XRs were performed in 188 patients and others had CT scan from the beginning. Only 2 out of 188 patients had abnormal findings on XR, which showed malposition of the electrode in one patient and a tip fold over and incomplete insertion in the other one. Both patients with abnormal findings had labyrinthitis ossificans. The patient with tip fold over ultimately underwent re-implantation. Another patient with incomplete insertion had required extended basal turn drilling during implantation, and no additional measures were taken.

CONCLUSION

Routine XR findings did not provide the reason for additional intervention, and its benefit for patients without demonstrable cochlear abnormalities was minimal. Post-op XR can be informative in selected high risk patients, but CT imaging is a reasonable alternative to better define anatomic array location in patients particularly at risk.

Characterization of Tip Fold-Over Using Fluoroscopy and Intracochlear Pressure in Cadaver Specimens

OBJECTIVES

Cochlear implant array malpositioning is associated with impaired speech perception, vertigo, and facial nerve stimulation. Tip fold-over is a subset of malpositioning that occurs more often with perimodiolar electrodes, but historically it has not been characterized due to lack of knowledge regarding electrode movements of the electrode within the cochlea. The aim of this study was to characterize the mechanics of tip fold-over events and their associated insertion pressure profiles.

METHODS

Cadaveric human heads were surgically prepared with a mastoidectomy and facial recess. Fiberoptic pressure sensors were inserted into the scala vestibuli and tympani to measure intracochlear pressures. Perimodiolar CI electrodes (Cochlear Slim-Modiolar, CI532) were inserted via round window under fluoroscopy.

RESULTS

Three types of tip fold-over events were observed: anterior-posterior C-shaped, medial-lateral C-shaped, and S-shaped roll-overs. The largest transient pressures occurred with anterior-posterior and S-type roll-over, and were associated with rotation or twisting inside the cochlea.

CONCLUSIONS

Results demonstrate at least three subtypes of tip fold-overs. Elevated pressure transients were noted before and during the tip fold-over event related to electrode twisting. The characterization of tip fold-over into subtypes is novel and may aid identification of tip fold-over events intraoperatively in the future. It remains important to identify tip fold-over events, and they should be recognized early using a multimodal verification system. Further investigation is still required to determine the significance of these changes and other possible patterns of intracochlear electrode movement.

LEVEL OF EVIDENCE

NA: Cadaver study Laryngoscope, 135:1795-1802, 2025.

A Case Series Suggests Peaking Transimpedance as a Possible Marker for Scalar Dislocations in Cochlear Implantation

INTRODUCTION

During postoperative implant control, we observed extraordinary peaks in transimpedance measurements. While searching for a possible reason, it appeared that they might correlate with scalar dislocations.

METHODS

In this retrospective case series, six adult CI patients who underwent transimpedance measurements and postoperative imaging were analyzed. Intra- and postoperative transimpedance measurements were visual inspected. The intracochlear position of electrodes was radiologically identified.

RESULTS

From 6 patients with transimpedance matrices showing an extraordinary peak in the off-diagonal area, five electrode arrays showed no correct scalar localization in the scala tympani, and one had a correct scalar localization in the scala tympani.

CONCLUSIONS

A peaking transimpedance might be a marker for scalar dislocation in CIs.

Lessons learned in delayed identification of a misplaced electrode array in the vestibule

To report a case of cochlear implantation with a misplaced electrode array in the vestibule and the causes for the delay in identification. A 23-year-old male with left single-sided deafness underwent cochlear implantation. The intraoperative assessment did not reveal any major red flags of electrode array misplacement. He did not display any vestibular symptoms postoperatively but showed poor speech performance, even though the aided tone audiometry revealed good sound detection thresholds. High-resolution computed tomography (HRCT) showed that the entire perimodiolar electrode array was situated within the vestibule, and a revision surgery was conducted. Retrospective analysis of the neural response telemetry (NRT) revealed subtle differences in responses between the misplaced and correctly placed electrode arrays. Unlike previously reported cases, the patient did not display vestibular symptoms despite the misplacement of the electrode in the vestibule due to existing weakness in otolithic function. Further investigation is warranted when a motivated patient with normal inner ear anatomy does not show benefit with the cochlear implant post-operatively.

Utilization of SmartNav technology in cochlear implantation: optimizing efficiency in assessment of electrode placement

OBJECTIVES

Proper electrode placement is essential for favorable hearing outcomes following cochlear implantation. Though often used, traditional intraoperative X-ray imaging is time consuming, exposes patients and staff to radiation, and poses interpretational challenges. The Nucleus® SmartNav System, utilizes electrode voltage telemetry (EVT) to analyze the positioning of the electrode array intraoperatively. This study investigates the efficacy of SmartNav in optimizing the efficiency and accuracy of assessing electrode placement.

METHODS

This prospective clinical study analyzed placement of 50 consecutive Cochlear Corporation cochlear implants conducted at a single institution between March of 2022 and June of 2023. Placement check of electrode array using SmartNav and X-ray was completed and individually assessed. A comparative analysis of SmartNav and X-ray completion times for electrode placement assessment was conducted.

RESULTS

Subjects included nine ears with abnormal anatomy and three reimplants. SmartNav placement check required a total time of 2.12 min compared to X-ray imaging at 14.23 min (p = 1.6E-16, CI 95%). Both SmartNav and X-ray had excellent sensitivity of 100% in identifying appropriate electrode position (p = 1.0). Tip fold-over was identified using both modalities in 3 cases with noted easier interpretation using SmartNav.

CONCLUSION

The Nucleus® SmartNav System significantly outperformed traditional X-ray imaging, offering a faster and more straightforward approach to assessing electrode positioning during cochlear implant surgery, thereby enhancing surgical efficiency and patient safety.

A scoping review on the clinical effectiveness of Trans-Impedance Matrix (TIM) measurements in detecting extracochlear electrodes and tip fold overs in Cochlear Ltd devices

BACKGROUND

Extrusion of electrodes outside the cochlea and tip fold overs may lead to suboptimal outcomes in cochlear implant (CI) recipients. Intraoperative measures such as Trans-Impedance Matrix (TIM) measurements may enable clinicians to identify electrode malposition and direct surgeons to correctly place the electrode array during surgery.

OBJECTIVES

To assess the current literature on the effectiveness of TIM measurements in identifying extracochlear electrodes and tip fold overs.

METHODS

A scoping review of studies on TIM-based measurements were carried out using the Databases-Medline/PubMed, AMED, EMBASE, CINAHL and the Cochrane Library following PRISMA guidelines. Eleven full texts articles met the inclusion criteria. Only human studies pertaining to TIM as a tool used in CI were included in the review. Further, patient characteristics, electrode design, and TIM measurement outcomes were reported.

RESULTS

TIM measurements were available for 550 implanted ears with the subjects age ranged between 9 months to 89 years. Abnormal TIM measurements were reported for 6.55% (36). Tip fold over was detected in 3.64% (20) of the cases, extracochlear electrodes in 1.45% (8), and 1.45% (8) were reported as buckling. Slim-modiolar electrode array designs were more common (54.71%) than pre-curved (23.34%) or lateral wall (21.95%) electrode array. Abnormal cochlear anatomy was reported for five ears (0.89%), with normal cochlear anatomy for all other patients.

CONCLUSION

TIM measurement is a promising tool for the intraoperative detection of electrode malposition. TIM measurement has a potential to replace intraoperative imaging in future. Though, TIM measurement is in its early stages of clinical utility, intuitive normative data sets coupled with standardised criteria for detection of abnormal electrode positioning would enhance its sensitivity.