Investigating Facial Nerve Stimulation After Cochlear Implantation in Adult and Pediatric Recipients

Exploring cross-modal plasticity in the auditory-visual cortex post cochlear implantation: implications for auditory and speech function recovery and mechanisms

Objective

The aim of this is to explore changes in cross-modal reorganization within the auditory-visual cortex after cochlear implantation, examining their influence on auditory and speech functions along with their underlying mechanisms.

Methods

Twenty prelingually deaf children who received cochlear implantation and rehabilitation training at our hospital between February 2022 and February 2023 comprised the prelingual deaf group. Simultaneously, 20 healthy children served as the control group. The prelingual deaf group underwent brain cortical activity assessment and evaluation of auditory-speech recovery pre-surgery, at postoperative weeks 1 and 2, and at months 1, 3, 6, 9, and 12. The control group underwent parallel assessments and evaluations. We analyzed the correlation between cortical activity in the auditory-visual cortex of patients and their auditory-speech functional recovery.

Results

The group with prelingual deafness displayed elevated levels of auditory and visual cortical electromagnetic intensity compared to the control group, both prior to and 9 months after surgery. However, by the 12-month mark post-surgery, there was no discernible distinction between the two groups. Following surgery, the prelingually deaf group exhibited a progressive improvement in both Categories of Auditory Performance (CAP) and Speech Intelligibility Rate (SIR), initially lagging behind the control group. Notably, a negative correlation emerged between auditory and visual cortical electromagnetic intensity values and CAP/SIR scores at the 12-month post-surgery assessment.

Conclusion

Cochlear implantation in prelingually deaf children results in elevated activity within the auditory and visual cortices, demonstrated by heightened electromagnetic intensity readings. Cross-modal reorganization is observed temporarily at 3 months post-surgery, which resolves to baseline levels by 12 months post-surgery. This phenomenon of reversal correlates with the restoration of auditory and speech functions in these children.

Hearing Performance in Cochlear Implant Users Who Have Facial Nerve Stimulation

Introduction  Facial nerve stimulation (FNS) is a complication in cochlear implant (CI) when the electrical current escapes from the cochlea to the nearby facial nerve. Different management to reduce its effects are available, although changes might result in a less-than-ideal fitting for the CI user, eventually reducing speech perception. Objective  To verify the etiologies that cause FNS, to identify strategies in managing FNS, and to evaluate speech recognition in patients who present FNS. Methods  Retrospective study approved by the Ethical Board of the Institution. From the files of a CI group, patients who were identified with FNS either during surgery or at any time postoperatively were selected. Data collection included: CI manufacturer, electrode array type, age at implantation, etiology of hearing loss, FNS identification date, number of electrodes that generated FNS, FNS management actions, and speech recognition in quiet and in noise. Results  Data were collected from 7 children and 25 adults. Etiologies that cause FNS were cochlear malformation, head trauma, meningitis, and otosclerosis; the main actions included decrease in the stimulation levels followed by the deactivation of electrodes. Average speech recognition in quiet before FNS was 86% and 80% after in patients who were able to accomplish the test. However, there was great variability, ranging from 0% in quiet to 90% of speech recognition in noise. Conclusion  Etiologies that cause FNS are related to cochlear morphology alterations. Facial nerve stimulation can be solved using speech processor programming parameters; however, it is not possible to predict outcomes, since results depend on other variables.

Risk factors and management strategies of inadvertent facial nerve stimulation in cochlear implant recipients: A systematic review

Objectives

To systematically review the prevalence and risk factors of inadvertent facial nerve stimulation (FNS) after cochlear implant (CI) surgery. And to report the different management strategies used for reducing and resolving FNS.

Data Source

Web of Science, Scopus, PubMed, Cochrane Library, and Virtual Health Library (VHL) of the World Health Organization (WHO).

Review Methods

A systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) on studies that reported FNS as a complication after CI. A comprehensive electronic search strategy was used to identify the relevant articles. We extracted the data on the prevalence of FNS after CI activation, the reported grades, and the management strategies. The number of associated electrodes; cause of deafness; co-anomalies; and duration of hearing loss and their relationships with FNS were also studied.

Results

Twenty-one relevant articles were included in this review. The prevalence of FNS among the CI populations was 5.29% (175/3306 patients). Among those whose ages were reported, 58.3% (95/163) were adults, and 41.7% (68/163) were pediatrics. Modifying the different fitting parameters was the most used strategy, as it successfully resolved FNS in 85.5% of the patients (142/166). The second commonly used management strategy was surgical intervention (reimplantation or explantation), which was reported in seven studies for 23 patients.

Conclusion

FNS after CI activation could be controlled and resolved with many advances that range from readjusting the fitting parameters to surgical intervention. However, further studies are required to validate the efficacy of each management strategy and its impact on patients' performance. Our findings demonstrate that CI recipients with FNS could still benefit from the CI devices and their FNS could be controlled.

Anodic Polarity Minimizes Facial Nerve Stimulation as a Side Effect of Cochlear Implantation

One severe side effect of the use of cochlear implants (CI) is coincidental facial nerve stimulation (FNS). Clinical methods to alleviate FNS range from the reprogramming of processor settings to revision surgery. We systematically assessed different changes in CI stimulation modes that have been discussed in the literature as "rescue factors" from FNS: electrode configuration (broad to focused), pulse shape (symmetric biphasic to pseudo-monophasic), and pulse polarity (cathodic to anodic). An FNS was assessed, based on electrophysiological thresholds, in 204 electrically evoked compound action potential (eCAP) input/output functions recorded from 33 ears of 26 guinea pigs. The stimulation level difference between auditory nerve eCAP threshold and FNS threshold was expressed as the eCAP-to-FNS offset. Coincidental FNS occurred in all animals and in 45% of all recordings. A change from monopolar to focused (bipolar, tripolar) configurations minimized FNS. The Euclidean distance between the CI contacts and the facial nerve explained no more than 33% of the variance in FNS thresholds. For both the FNS threshold and the eCAP-to-FNS offset, the change from cathodic to anodic pulse polarity significantly reduced FNS and permitted a gain of 14-71% of the dynamic range of the eCAP response. This "anodic rescue effect" was stronger for pseudo-monophasic pulses as compared to the symmetric biphasic pulse shape. These results provide possible mechanisms underlying recent clinical interventions to alleviate FNS. The "anodic-rescue effect" may offer a non-invasive therapeutic option for FNS in human CI users that should be tested clinically, preferably in combination with current-focusing methods.

Cochlear re-implantation with the use of multi-mode grounding associated with anodic monophasic pulses to manage abnormal facial nerve stimulation

Objectives: To investigate the outcomes of cochlear re-implantation using multi-mode grounding stimulation associated with anodic monophasic pulses to manage abnormal facial nerve stimulation (AFNS) in cochlear implant (CI) recipients. Methods: Retrospective case report. An adult CI recipient with severe AFNS and decrease in auditory performance was re-implanted with a new CI device to change the pulse shape and stimulation mode. Patient's speech perception scores and AFNS were compared before and after cochlear re-implantation, using monopolar stimulation associated with cathodic biphasic pulses and multi-mode stimulation mode associated to anodic monophasic pulses, respectively. The insertion depth angle and the electrode-nerve distances were also investigated, before and after cochlear re-implantation. Results: AFNS was resolved, and the speech recognition scores rapidly increased in the first year after cochlear re-implantation while remaining stable. After cochlear re-implantation, the e15 and e20 electrodes showed shorter electrode-nerve distances compared to their correspondent e4 and e7 electrodes, which induced AFNS in the first implantation. Conclusions: Cochlear re-implantation with multi-mode grounding stimulation associated with anodic monophasic pulses was an effective strategy for managing AFNS. The patient's speech perception scores rapidly improved and AFNS was not detected four years after cochlear re-implantation.

Facial nerve stimulation in adult cochlear implant recipients with far advanced otosclerosis

Objectives

The objective of this study was to predict occurrence of facial nerve stimulation (FNS) in cochlear implanted patients for far-advanced otosclerosis (FAO) by correlating preoperative computed tomography (CT)-scan data to FNS and to evaluate FNS impact on hearing outcomes.

Methods

Retrospective analysis on 91 ears (76 patients) implanted for FAO. Electrodes were straight (50%) or perimodiolar (50%). Demographic data, extension of otosclerosis on preoperative CT scan, occurrence of FNS, and speech performance were analyzed.

Results

Prevalence of FNS was 21% (19 ears). FNS appeared during the first month (21%), 1-6 months (26%), 6-12 months (21%), and over 1 year (32%) postimplantation. Cumulative incidence of FNS at 15 years was 33% (95% CI = [14-47%]). Extension of otosclerotic lesions on preimplantation CT-scan was more severe in FNS ears compared to No-FNS (p < .05): for Stage III, 13/19 (68%) and 18/72 (25%) ears for FNS and No-FNS groups, respectively (p < .05). Location of otosclerotic lesions relative to the facial nerve canal was similar whatever the presence or not of FNS. Electrode array had no impact on FNS occurrence. At 1 year post-implantation, duration of profound hearing loss (≥5 years) and previous stapedotomy were negatively associated with speech performance. FNS did not impact hearing outcomes, despite a lower percentage of activated electrodes (p < .01) in the FNS group. Nevertheless, FNS were associated with a decrease of speech performance both in quiet (p < .001) and in noise (p < .05).

Conclusion

Cochlear implanted patients for FAO are at greater risk of developing FNS affecting speech performance over time, probably due to a higher percentage of deactivated electrodes. High resolution CT-scan is an essential tool allowing FNS prediction but not time of onset.

Level of evidence

2b, Laryngoscope Investigative Otolaryngology, 2022.

Recent advancements in bioelectronic devices to interface with the peripheral vestibular system

Balance disorders affect approximately 30% of the population throughout their lives and result in debilitating symptoms, such as spontaneous vertigo, nystagmus, and oscillopsia. The main cause of balance disorders is peripheral vestibular dysfunction, which may occur as a result of hair cell loss, neural dysfunction, or mechanical (and morphological) abnormality. The most common cause of vestibular dysfunction is arguably vestibular hair cell damage, which can result from an array of factors, such as ototoxicity, trauma, genetics, and ageing. One promising therapy is the vestibular prosthesis, which leverages the success of the cochlear implant, and endeavours to electrically integrate the primary vestibular afferents with the vestibular scene. Other translational approaches of interest include stem cell regeneration and gene therapies, which aim to restore or modify inner ear receptor function. However, both of these techniques are in their infancy and are currently undergoing further characterization and development in the laboratory, using animal models. Another promising translational avenue to treating vestibular hair cell dysfunction is the potential development of artificial biocompatible hair cell sensors, aiming to replicate functional hair cells and generate synthetic 'receptor potentials' for sensory coding of vestibular stimuli to the brain. Recently, artificial hair cell sensors have demonstrated significant promise, with improvements in their output, such as sensitivity and frequency selectivity. This article reviews the history and current state of bioelectronic devices to interface with the labyrinth, spanning the vestibular implant and artificial hair cell sensors.

Mythbusters! The Truth about Common Misconceptions in Cochlear Implantation

Cochlear implantation (CI) is the preferred method of hearing rehabilitation when patients cannot perform well with traditional amplification. Unfortunately, there are still significant misconceptions around this life-changing intervention. The goal of this article is to address some of the most common myths around CI surgery. After reading this article, the learner will be able to explain the utility of CI in patients with residual hearing and recognize that insurance coverage is widespread. The reader will be able to list common risks associated with this well-tolerated procedure including anesthetic risk and the risk of vestibular dysfunction. Additionally, the reader will be able to identify the significant positive impact of CI on patients' quality of life. Finally, the reader will identify that many patients can safely have an MRI scan after implantation, including nearly all contemporary recipients.

Risk Factors for Facial Nerve and Other Nonauditory Side Effects Following Cochlear Implantation

OBJECTIVE

The purpose of this study was to characterize a cohort of patients with nonauditory side-effects (NASx) following cochlear implant (CI) surgery.

STUDY DESIGN

Retrospective case review.

SETTING

Tertiary referral center.

PATIENTS

One hundred twenty three multichannel CI recipients with intraoperative facial nerve stimulation (FNS).

INTERVENTIONS

Intraoperative electrical auditory brainstem responses (eABR) during CI surgery.

MAIN OUTCOME MEASURES

Nonauditory side effects post-CI activation.

RESULTS

Intraoperative FNS was identified in 2.26% of patients (123/5441), of whom, 34% (42/123) experienced VII stimulation on CI activation. Pain was experienced by 22% (27/123) and vestibular dysfunction was experienced by 4% (5/123) of cases. All case who experienced pain and/or vestibular NASx also experienced VII stimulation. The majority of cases were managed by CI remapping or observation and habituation.Significant relationships were found between etiology of hearing loss and presence of FNS upon initial activation (p < 0.05). No significance was found between FNS intraoperatively and at initial activation for all assumed mechanisms of hearing loss (p > 0.05) with the exceptions of acquired hearing loss of undetermined etiology and toxic etiology group (p < 0.05).There was no significant impact of implant array design (p > 0.05).

CONCLUSIONS

This study has characterized patients with NASx in a large cohort of CI patients. One third of cases identified with FNS intraoperatively, developed NASx post-CI activation. Risk factors for NASx postactivation include high-risk etiologies and intraoperative objective measures (i.e., eABR). This may assist surgeons and audiologists to identify at-risk patients who may need modifications in CI program planning.

Signal processing & audio processors

Signal processing algorithms are the hidden components in the audio processor that converts the received acoustic signal into electrical impulses while maintaining as much relevant information as possible. Signal processing algorithms should be smart enough to mimic the functionality of external, middle and the inner-ear to provide the cochlear implant (CI) user with a hearing experience as natural as possible. Modern sound processing strategies are based on the continuous interleaved sampling (CIS) strategy proposed by B. Wilson in 1991, which provided envelope information over several intracochlear electrodes. The CIS strategy brought significant gains in speech perception. Translational research activities of MED-EL resulted in further improvements in speech understanding in noisy environments as well as enjoyment of music by not only coding CIS-based envelope information, but by also representing temporal fine structure information in the stimulation patterns of the apical channels. Further developments include "complete cochlear coverage" made possible by deep insertion of the intracochlear electrode, elaborate front end processing, anatomy based fitting (ABF), triphasic pulse stimulation instrumental in the suppression of facial nerve stimulation, and bimodal delay compensation allowing unilateral CI users to experience hearing with hearing aids on the contralateral ear. The large number of hardware developments might be exemplified by the RONDO, the world's first single unit audio processor in 2013. This article covers the milestones of translational research around the signal processing and audio processor topic that took place in association with MED-EL.

Evaluation of computed tomography parameters in patients with facial nerve stimulation post-cochlear implantation

PURPOSE

To compare the preoperative computed tomography (CT) parameters, including the thickness and density of the bone separating the upper basal turn of the cochlea (UBTC) and the labyrinthine segment of the facial nerve (LSFN), in patients with and without facial nerve stimulation (FNS) in post-cochlear implants (CI).

METHODS

A retrospective case review of 1700 CI recipients in a tertiary referral center between January 2010 and January 2020 was performed; out of the 35 recipients who were found to have FNS, 29 were included in the study. The control group comprised the same number of randomly selected patients. CT parameters of the patients were measured independently by three fellowship-trained neuro-otologists blinded to the postoperative status of the patients. Thickness in axial and coronal views and density of the bone separating the UBTC and the LSFN were measured.

RESULT

There was satisfactory agreement between the readings of the three reviewers. The distances (in mm) between the UBTC and LSFN obtained from the coronal (0.43 ± 0.24 vs. 0.63 ± 0.2) and axial (0.42 ± 0.25 vs. 0.6 ± 0.18) views were statistically lower in the FNS group (p = 0.001 and 0.005, respectively). The density (in HU) of the bony partition was also statistically lower in the FNS group (1038 ± 821 vs. 1409 ± 519; p = 0.029).

CONCLUSION

Patients who experienced FNS postoperatively had significantly lower distance and bone density between the UBTC and the LSFN. This finding can help surgeons in preoperative planning in an attempt to decrease the occurrence of FNS.

Performance of cochlear implant recipients fitted with triphasic pulse patterns

PURPOSE

To assess the effect of triphasic pulse pattern stimulation strategy on the audiological performance of cochlear implant recipients with unintended facial nerve stimulation (FNS), and to compare the audiological and speech outcomes before and after switching to triphasic stimulation.

METHODS

A retrospective study of patients who have changed their fitting maps from biphasic to triphasic pulse pattern stimulation because of FNS after cochlear implantation (CI). All identified patients with FNS after CI from 2017 to 2019 were included in this study. The medical records of 11 patients (16 ears) were queried for demographic and radiological data, pure tone audiometry, speech reception thresholds, speech discrimination score at 65 dB, maximum comfortable levels, thresholds, and dynamic range. Then, these parameters were compared in the two conditions, biphasic and triphasic.

RESULTS

Using triphasic pulse stimulation only or combined with switch-off of few channels, complete resolution of FNS was achieved. Triphasic pulse pattern stimulation was associated with better speech discrimination scores (75.25 ± 26.13%) compared to the biphasic pulse (58.25 ± 26.13%). This triphasic strategy also showed higher maximum comfortable levels (36.62 ± 1.63 qu) than biphasic strategy (31.58 ± 2.5 qu). Moreover, the dynamic range was wider using triphasic pulse strategy. In general, the triphasic pulse pattern resulted in successful suppression of facial nerve stimulation with suitable maximum comfortable levels and better speech discrimination.

CONCLUSION

Triphasic pulse pattern stimulation is an appropriate tool in controlling FNS following cochlear implantation with wider dynamic range. We recommend that all patients with facial nerve stimulation after CI surgery be switched to a triphasic pulse program prior to considering further surgery.