A new electrode for residual hearing preservation in cochlear implantation: first clinical results

Chronic Electro-Acoustic Stimulation May Interfere With Electric Threshold Recovery After Cochlear Implantation in the Aged Guinea Pig

OBJECTIVES

Electro-acoustic stimulation (EAS) combines electric stimulation via a cochlear implant (CI) with residual low-frequency acoustic hearing, with benefits for music appreciation and speech perception in noise. However, many EAS CI users lose residual acoustic hearing, reducing this benefit. The main objectives of this study were to determine whether chronic EAS leads to more hearing loss compared with CI surgery alone in an aged guinea pig model, and to assess the relationship of any hearing loss to histology measures. Conversely, it is also important to understand factors impacting efficacy of electric stimulation. If one contributor to CI-induced hearing loss is damage to the auditory nerve, both acoustic and electric thresholds will be affected. Excitotoxicity from EAS may also affect electric thresholds, while electric stimulation is osteogenic and may increase electrode impedances. Hence, secondary objectives were to assess how electric thresholds are related to the amount of residual hearing loss after CI surgery, and how EAS affects electric thresholds and impedances over time.

DESIGN

Two groups of guinea pigs, aged 9 to 21 months, were implanted with a CI in the left ear. Preoperatively, the animals had a range of hearing losses, as expected for an aged cohort. At 4 weeks after surgery, the EAS group (n = 5) received chronic EAS for 8 hours a day, 5 days a week, for 20 weeks via a tether system that allowed for free movement during stimulation. The nonstimulated group (NS; n = 6) received no EAS over the same timeframe. Auditory brainstem responses (ABRs) and electrically evoked ABRs (EABRs) were recorded at 3 to 4 week intervals to assess changes in acoustic and electric thresholds over time. At 24 weeks after surgery, cochlear tissue was harvested for histological evaluation, only analyzing animals without electrode extrusions (n = 4 per ear).

RESULTS

Cochlear implantation led to an immediate worsening of ABR thresholds peaking between 3 and 5 weeks after surgery and then recovering and stabilizing by 5 and 8 weeks. Significantly greater ABR threshold shifts were seen in the implanted ears compared with contralateral, non-implanted control ears after surgery. After EAS and termination, no significant additional ABR threshold shifts were seen in the EAS group compared with the NS group. A surprising finding was that NS animals had significantly greater recovery in EABR thresholds over time, with decreases (improvements) of -51.8 ± 33.0 and -39.0 ± 37.3 c.u. at 12 and 24 weeks, respectively, compared with EAS animals with EABR threshold increases (worsening) of +1.0 ± 25.6 and 12.8 ± 44.3 c.u. at 12 and 24 weeks. Impedance changes over time did not differ significantly between groups. After exclusion of cases with electrode extrusion or significant trauma, no significant correlations were seen between ABR and EABR thresholds, or between ABR thresholds with histology measures of inner/outer hair cell counts, synaptic ribbon counts, stria vascularis capillary diameters, or spiral ganglion cell density.

CONCLUSIONS

The findings do not indicate that EAS significantly disrupts acoustic hearing, although the small sample size limits this interpretation. No evidence of associations between hair cell, synaptic ribbon, spiral ganglion cell, or stria vascularis with hearing loss after cochlear implantation was seen when surgical trauma is minimized. In cases of major trauma, both acoustic thresholds and electric thresholds were elevated, which may explain why CI-only outcomes are often better when trauma and hearing loss are minimized. Surprisingly, chronic EAS (or electric stimulation alone) may negatively impact electric thresholds, possibly by prevention of recovery of the auditory nerve after CI surgery. More research is needed to confirm the potentially negative impact of chronic EAS on electric threshold recovery.

Outcomes following cochlear implantation with eluting electrodes: A systematic review

Objectives

To establish audiological and other outcomes following cochlear implantation in humans and animals with eluting electrodes.

Methods

Systematic review and narrative synthesis. Databases searched (April 2023): MEDLINE, EMBASE, CENTRAL, ClinicalTrials.gov, and Web of Science. Studies reporting outcomes in either humans or animals following cochlear implantation with a drug-eluting electrode were included. No limits were placed on language or year of publication. Risk of bias assessment was performed on all included studies using either the Brazzelli or Systematic Review Centre for Laboratory animal Experimentation (SYRCLE) assessment tools. The review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 statement.

Results

Searches identified 146 abstracts and 108 full texts. Of these, 18 studies met the inclusion criteria, reporting outcomes in 523 animals (17 studies) and 24 humans (1 study). Eluting electrodes included dexamethasone (16 studies), aracytine (1 study), nicotinamide adenine dinucleotide (1 study), the growth factors insulin-like growth factor 1 (IGF1) and hepatocyte growth factor (HGF) (1 study), and neurotrophin-3 (1 study). All included studies compare outcomes following implantation with an eluting electrode with a control non-eluting electrode. In the majority of studies, audiological outcomes (e.g., auditory brainstem response threshold) were superior following implantation with an eluting electrode compared with a standard electrode. Most studies which investigated post-implantation impedance reported lower impedance following implantation with an eluting electrode. The influence of eluting electrodes on other reported outcomes (including post-implantation cochlear fibrosis and the survival of hair cells and spiral ganglion neurons) was more varied across the included studies.

Conclusions

Eluting electrodes have shown promise in animal studies in preserving residual hearing following cochlear implantation and in reducing impedance, though data from human studies remain lacking. Further in-human studies will be required to determine the clinical usefulness of drug-eluting cochlear implants as a future treatment for sensorineural hearing loss.

Preservation of Residual Hearing: Long-Term Results With a Mid-Scala Electrode

OBJECTIVE

The long-term preservation of residual hearing after cochlear implantation has become a major goal over the past few years. The aim of the present study was to evaluate residual hearing in the long-term follow-up using mid-scala electrodes.

METHODS

In this retrospective, single-center study, we collected data from 27 patients who were implanted between 2014 and 2015 with residual hearing in the low-frequency range using a mid-scala electrode. Measurements of the hearing thresholds were carried out directly postoperatively (day 1 after surgery) and in the long-term follow-up 43.7 ± 6.9 months. The calculation of the extent of audiological hearing preservation was determined using the HEARRING group formula by Skarsynski.

RESULTS

Postoperative preservation of residual hearing was achieved in 69.2% of the cases in the low-frequency range between 250 Hz and 1 kHz, of which 89.5% of the patients had frequencies that suggested using electroacoustic stimulation (EAS). In the long-term follow-up, 30.8% of the patients showed residual hearing; however, 57.1% had apparently benefited from EAS.

CONCLUSION

Preservation of residual hearing is feasible in the long term using mid-scala electrodes. Postoperatively, there is over the half of patients who benefit from an EAS strategy. The long-term follow-up shows a certain decrease in residual hearing. However, these results are comparable to studies relating to other types of electrodes. Further research should be conducted in future to better evaluate hearing loss in long-term follow-up, compared to direct postoperative audiological results.

Residual low-frequency hearing after early device activation in cochlear implantation

PURPOSE

The cochlear implant (CI) is a standard treatment for patients with severe to profound hearing loss. In recent years, early device activation of the sound processor after 2-3 days following surgery has been established. The aim of this study is to evaluate the residual hearing of CI patients with substantial preoperative low-frequency hearing after early device activation over a period of 12 months.

METHODS

Results were compared between an early fitted group (EF) with device activation to less than 15 days after CI surgery and a control group (CG) with device activation after 3-6 weeks. In total, 57 patients were divided into EF group (n = 32), and CG (n = 25). Low-frequency residual hearing and speech recognition in quiet and in noise were compared over an observation period of 12 months.

RESULTS

No significant difference (p > 0.05) in the residual low-frequency hearing PTAlow between EF and CG was found, neither preoperatively (EF 33.2 dB HL/CG 35.0 dB HL), nor postoperatively (EF 46.8 dB HL/CG 46.2 dB HL). In both groups, postoperative residual hearing decreased compared to preoperative and remained stable within the first year after CI surgery. Furthermore, both groups showed no significant differences (p > 0.05) in speech recognition in quiet and in noise within the first year.

CONCLUSION

Early device activation is feasible in CI patients with preoperative low-frequency residual hearing, without an additional effect on postoperative hearing preservation.

Nanocatalysts as fast and powerful medical intervention: Bridging cochlear implant therapies and advanced modelling using Hidden Markov Models (HMMs) for effective treatment of infections

As human population growth and waste from technologically advanced industries threaten to destabilise our delicate ecological equilibrium, the global spotlight intensifies on environmental contamination and climate-related changes. These challenges extend beyond our external environment and have significant effects on our internal ecosystems. The inner ear, which is responsible for balance and auditory perception, is a prime example. When these sensory mechanisms are impaired, disorders such as deafness can develop. Traditional treatment methods, including systemic antibiotics, are frequently ineffective due to inadequate inner ear penetration. Conventional techniques for administering substances to the inner ear fail to obtain adequate concentrations as well. In this context, cochlear implants laden with nanocatalysts emerge as a promising strategy for the targeted treatment of inner ear infections. Coated with biocompatible nanoparticles containing specific nanocatalysts, these implants can degrade or neutralise contaminants linked to inner ear infections. This method enables the controlled release of nanocatalysts directly at the infection site, thereby maximising therapeutic efficacy and minimising adverse effects. In vivo and in vitro studies have demonstrated that these implants are effective at eliminating infections, reducing inflammation, and fostering tissue regeneration in the ear. This study investigates the application of hidden Markov models (HMMs) to nanocatalyst-loaded cochlear implants. The HMM is trained on surgical phases in order to accurately identify the various phases associated with implant utilisation. This facilitates the precision placement of surgical instruments within the ear, with a location accuracy between 91% and 95% and a standard deviation between 1% and 5% for both sites. In conclusion, nanocatalysts serve as potent medicinal instruments, bridging cochlear implant therapies and advanced modelling utilising hidden Markov models for the effective treatment of inner ear infections. Cochlear implants loaded with nanocatalysts offer a promising method to combat inner ear infections and enhance patient outcomes by addressing the limitations of conventional treatments.

Acceptance and Benefit of Electroacoustic Stimulation in Children

OBJECTIVE

Children with high-frequency severe-to-profound hearing loss and low-frequency residual hearing who do not derive significant benefit from hearing aids are now being considered for cochlear implantation. Previous research shows that hearing preservation is possible and may be desirable for the use of electroacoustic stimulation (EAS) in adults, but this topic remains underexplored in children. The goal of this study was to explore factors relating to hearing preservation, acceptance, and benefits of EAS for children.

STUDY DESIGN

Retrospective review.

SETTING

Tertiary academic medical center.

PATIENTS

Forty children (48 ears) with preoperative low-frequency pure-tone averages of 75 dB HL or less at 250 and 500 Hz (n = 48).

INTERVENTION

All patients underwent cochlear implantation with a standard-length electrode.

MAIN OUTCOME MEASURE

Low-frequency audiometric thresholds, speech perception, and EAS usage were measured at initial stimulation, and 3 and 12 months postoperatively. Outcomes were compared between children with and without hearing preservation, and between EAS users and nonusers.

RESULTS

Hearing was preserved at similar rates as adults but worse for children with an enlarged vestibular aqueduct. Fewer than half of children who qualified to use EAS chose to do so, citing a variety of audiologic and nonaudiologic reasons. No differences were detected in speech perception scores across the groups for words, sentences, or sentences in noise tests.

CONCLUSIONS

Neither hearing preservation nor EAS use resulted in superior speech perception in children with preoperative residual hearing; rather, all children performed well after implantation.

Mild therapeutic hypothermia protects against inflammatory and proapoptotic processes in the rat model of cochlear implant trauma

OBJECTIVE

Mild therapeutic hypothermia (MTH) has been demonstrated to prevent residual hearing loss from surgical trauma associated with cochlear implant (CI) insertion. Here, we aimed to characterize the mechanisms of MTH-induced hearing preservation in CI in a well-established preclinical rodent model.

APPROACH

Rats were divided into four experimental conditions: MTH-treated and implanted cochleae, cochleae implanted under normothermic conditions, MTH only cochleae and un-operated cochleae (controls). Auditory brainstem responses (ABRs) were recorded at different time points (up to 84 days) to confirm long-term protection and safety of MTH locally applied to the cochlea for 20 min before and after implantation. Transcriptome sequencing profiling was performed on cochleae harvested 24 h post CI and MTH treatment to investigate the potential beneficial effects and underlying active gene expression pathways targeted by the temperature management.

RESULTS

MTH treatment preserved residual hearing up to 3 months following CI when compared to the normothermic CI group. In addition, MTH applied locally to the cochleae using our surgical approach was safe and did not affect hearing in the long-term. Results of RNA sequencing analysis highlight positive modulation of signaling pathways and gene expression associated with an activation of cellular inflammatory and immune responses against the mechanical damage caused by electrode insertion.

SIGNIFICANCE

These data suggest that multiple and possibly independent molecular pathways play a role in the protection of residual hearing provided by MTH against the trauma of cochlear implantation.

Four-point Impedance Changes in the Early Post-Operative Period After Cochlear Implantation

OBJECTIVE

Monitoring four-point impedance changes after cochlear implantation with comparison to conventional impedance measurements. Four-point impedance provides information regarding the bulk biological environment surrounding the electrode array, which is not discernible with conventional impedances.

STUDY DESIGN

Prospective observational.

SETTING

Hospital.

PATIENTS

Adult cochlear implant recipients with no measurable hearing before implantation and implanted with a perimodiolar cochlear implant.

MAIN OUTCOME MEASURES

Mean values for four-point and common ground impedances were calculated for all electrode contacts at intra-operative, 1 day, 1 week, 4 to 6 weeks, and 3 months post implantation. Linear mixed models were applied to the impedance data to compare between impedances and time points. Furthermore, patients were divided into groups dependent on the normalized change in four-point impedance from intra-operative to 1 day post-operative. The normalized change was then calculated for all other time points and compared across the two groups.

RESULTS

Significant increases in four-point impedance occurred 1 day and 3 months after surgery, particularly in the basal half of the array. Four-point impedance at 1 day was highly predictive of four-point impedance at 3 months. Four-point impedance at the other time points showed marginal or no increases from intra-operative. Patients with an average increase higher than 10% in four-point impedance from intra-operative to 1 day, had significantly higher values at 3 months ( p = 0.012). These patterns were not observed in common ground impedance.

CONCLUSION

This is the first study to report increases in four-point impedance within 24 hours of cochlear implantation. The increases at 1 day and 3 months align with the natural timeline of an acute and chronic inflammatory responses.

Systematic Literature Review of Hearing Preservation Rates in Cochlear Implantation Associated With Medium- and Longer-Length Flexible Lateral Wall Electrode Arrays

Background

The last two decades have demonstrated that preoperative functional acoustic hearing (residual hearing) can be preserved during cochlear implant (CI) surgery. However, the relationship between the electrode array length and postoperative hearing preservation (HP) with lateral wall flexible electrode variants is still under debate.

Aims/Objectives

This is a systematic literature review that aims to analyze the HP rates of patients with residual hearing for medium-length and longer-length lateral wall electrodes.

Method

A systematic literature review methodology was applied following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) recommendations to evaluate the HP rates of medium-length and longer-length lateral wall electrodes from one CI manufacturer (medium length FLEX 24, longer length FLEX 28 and FLEX SOFT, MED-EL, Innsbruck, Austria). A search using search engine PubMed (https://www.ncbi.nlm.nih.gov/pubmed/) was performed using the search terms “hearing preservation” or “residual hearing” and “cochlear implant” in “All fields.” Articles published only in English between January 01, 2009 and December 31, 2020 were included in the search.

Results

The HP rate was similar between medium-length (93.4%–93.5%) and longer (92.1%–86.8%) electrodes at 4 months (p = 0.689) and 12 months (p = 0.219). In the medium-length electrode group, patients under the age of 45 years had better HP than patients above the age of 45 years.

Conclusions

Both medium-length and longer electrode arrays showed high hearing preservation rates. Considering the hearing deterioration over time, implanting a longer electrode at primary surgery should be considered, thus preventing the need for future reimplantation.

Increased Threshold and Reduced Firing Rate of Auditory Cortex Neurons after Cochlear Implant Insertion

The cochlear implant (CI) is the most successful neuroprosthesis allowing thousands of patients with profound hearing loss to recover speech understanding. Recently, cochlear implants have been proposed to subjects with residual hearing and, in these cases, shorter CIs were implanted. To be successful, it is crucial to preserve the patient’s remaining hearing abilities after the implantation. Here, we quantified the effects of CI insertion on the responses of auditory cortex neurons in anesthetized guinea pigs. The responses of auditory cortex neurons were determined before and after the insertion of a 300 µm diameter CI (six stimulating electrodes, length 6 mm). Immediately after CI insertion there was a 5 to 15 dB increase in the threshold for cortical neurons from the middle to the high frequencies, accompanied by a decrease in the evoked firing rate. Analyzing the characteristic frequency (CF) values revealed that in large number of cases, the CFs obtained after insertion were lower than before. These effects were not detected in the control animals. These results indicate that there is a small but immediate cortical hearing loss after CI insertion, even with short length CIs. Therefore, efforts should be made to minimize the damages during CI insertion to preserve the cortical responses to acoustic stimuli.

A Window of Opportunity: Perilymph Sampling from the Round Window Membrane Can Advance Inner Ear Diagnostics and Therapeutics

In the clinical setting, the pathophysiology of sensorineural hearing loss is poorly defined and there are currently no diagnostic tests available to differentiate between subtypes. This often leaves patients with generalized treatment options such as steroids, hearing aids, or cochlear implantation. The gold standard for localizing disease is direct biopsy or imaging of the affected tissue; however, the inaccessibility and fragility of the cochlea make these techniques difficult. Thus, the establishment of an indirect biopsy, a sampling of inner fluids, is needed to advance inner ear diagnostics and allow for the development of novel therapeutics for inner ear disease. A promising source is perilymph, an inner ear liquid that bathes multiple structures critical to sound transduction. Intraoperative perilymph sampling via the round window membrane of the cochlea has been successfully used to profile the proteome, metabolome, and transcriptome of the inner ear and is a potential source of biomarker discovery. Despite its potential to provide insight into inner ear pathologies, human perilymph sampling continues to be controversial and is currently performed only in conjunction with a planned procedure where the inner ear is opened. Here, we review the safety of procedures in which the inner ear is opened, highlight studies where perilymph analysis has advanced our knowledge of inner ear diseases, and finally propose that perilymph sampling could be done as a stand-alone procedure, thereby advancing our ability to accurately classify sensorineural hearing loss.

One Year Assessment of the Hearing Preservation Potential of the EVO Electrode Array

Background: A prospective longitudinal multicentre study was conducted to assess the one-year postsurgical hearing preservation profile of the EVO^TM electrode array. Methods: Fifteen adults presenting indications of electro-acoustic stimulation (pure-tone audiometry (PTA) thresholds ≤70 dB below 750 Hz) were implanted with the EVO™ electrode array. Hearing thresholds were collected at five time-points from CI activation to twelve months (12M) after activation. Hearing thresholds and hearing preservation profiles (HEARRING group classification) were assessed. Results: All subjects had measurable hearing thresholds at follow-up. No case of complete loss of hearing or minimal hearing preservation was reported at any time point. At activation (N_act = 15), five participants had complete hearing preservation, and ten participants had partial hearing preservation. At the 12M time point (N_12m = 6), three participants had complete hearing preservation, and three participants had partial hearing preservation. Mean hearing loss at activation was 11 dB for full range PTA and 25 dB for PTAs low-frequency (125–500 Hz). Conclusions: This study provides the first longitudinal follow-up on associated hearing profiles to the EVO™ electrode array, which are comparable to the literature. However, other studies on larger populations should be performed.

Residual hearing preservation for cochlear implantation surgery

Cochlear implantation (CI) has developed for more than four decades. Initially, CI was used for profound bilateral hearing impairment. However, the indications for CI have expanded in recent years to include children with symptomatic partial deafness. Therefore, CI strategies to preserve residual hearing are important for both patients and otologists. The loss of residual low-frequency hearing is thought to be the result of many factors. All surgical methods have the same goal: protect the delicate intracochlear structures and preserve residual low-frequency hearing to improve speech perception abilities. Fully opening the round window membrane, a straight electrode array, slower insertion speed, and the use of corticosteroids result in a higher rate of hearing preservation. Several factors, like the way of surgical approaches, length of arrays and timing of activation, may not affect the residual hearing preservation. Therefore, the classic atraumatic technique, including the very slow and delicate insertion and administration of intraoperative corticosteroids, can improve hearing outcomes.

The role of oxidative stress in the susceptibility of noise-impaired cochleae to synaptic loss induced by intracochlear electrical stimulation

Intracochlear electrical stimulation (ES) generated by cochlear implants (CIs) is used to activate auditory nerves to restore hearing perception in deaf subjects and those with residual hearing who use electroacoustic stimulation (EAS) technology. Approximately 1/3 of EAS recipients experience loss of residual hearing a few months after ES activation, but the underlying mechanism is unknown. Clinical evidence indicates that the loss is related to the previous history of noise-induced hearing loss (NIHL). In this report, we investigated the impact of intracochlear ES on oxidative stress levels and synaptic counts in inner hair cells (IHCs) of the apical, middle and basal regions of guinea pigs with normal hearing (NH) and NIHL. Our results demonstrated that intracochlear ES with an intensity of 6 dB above the thresholds of electrically evoked compound action potentials (ECAPs) could induce the elevation of oxidative stress levels, resulting in a loss of IHC synapses near the electrodes in the basal and middle regions of the NH cochleae. Furthermore, the apical region of cochleae with NIHL were more susceptible to synaptic loss induced by relatively low-intensity ES than that of NH cochleae, resulting from the additional elevation of oxidative stress levels and the reduced antioxidant capability throughout the whole cochlea.

Hearing Preservation Outcomes With Standard Length Electrodes in Adult Cochlear Implantation and the Uptake of Electroacoustic Stimulation

BACKGROUND

Cochlear implantation with preservation of residual low-frequency hearing enables patients to utilize acoustic and electrical stimulation. It is widely accepted that preservation of residual low-frequency hearing is beneficial in both background noise and for music appreciation. The extent to which patients may benefit is not fully understood, but the importance of these concepts is reflected in electrode design developments and also refinement of surgical technique. Greater understanding is needed around factors that may affect hearing preservation. This study reports experience in adults using standard length cochlear implant arrays.

OBJECTIVE

The study reviews hearing preservation outcomes using the HEARRING GROUP method for factors such as gender, electrode type, insertion depth, laterality, preoperative hearing level, and time between surgery and audiogram. Furthermore, the study reviews rates of electroacoustic stimulation use in those with postoperative functional residual low-frequency hearing.

METHODOLOGY

Retrospective case series.

INCLUSION CRITERIA

preoperative ≤ 85 dB HL at 250 Hz and aged ≥ 18 years. The hearing preservation percentages were calculated using the HEARRING group formula S=[1 - ((PTApost - PTApre)/(PTAmax - PTApre))*100]%. Preservation of > 75% was considered complete, 25 to 75% partial, and 1 to 25% minimal. Standardized operative technique with facial recess approach, posterior tympanotomy, and minimally traumatic round window insertion was performed for each implant.

RESULTS

Fifty-three implantations in 52 patients met the inclusion criteria. The mean age at implantation was 55.5 years. The average time since the last audiogram was 10 months. The mean average total pre and postoperative pure-tone averages were 92.4 dB, 99.2 dB, respectively, using minimum reporting standards for adult cochlear Implant (CI). Thirty percent demonstrated complete hearing preservation, 35.8% partial hearing preservation, and 20.8% minimal hearing preservation. Overall, mean hearing preservation was 52.9%. Sex, age at implantation, insertion depth, lateral versus perimodiolar electrode, and preoperative hearing level did not statistically significantly affect rates of hearing preservation in our study. There was a statistically significant deterioration in hearing preservation outcomes difference at 3 months compared with 12 months postoperatively. Only two patients within our study out of 17 with functional postoperative hearing went on to use electroacoustic stimulation.

CONCLUSION

Hearing preservation varies between patients and postoperative outcomes are difficult to predict. This study adds to existing literature in terms of likelihood of hearing preservation following cochlear implantation. In turn, this improves our ability to counsel patients as to the chances of preserving residual low-frequency hearing postoperatively and their ability to use electroacoustic stimulation.

Molecular mechanisms and roles of inflammatory responses on low-frequency residual hearing after cochlear implantation

Preservation of low-frequency residual hearing is very important for combined electro-acoustic stimulation after cochlear implantation. However, in clinical practice, loss of low-frequency residual hearing often occurs after cochlear implantation and its mechanisms remain unclear. Factors affecting low-frequency residual hearing after cochlear implantation are one of the hot spots in current research. Inflammation induced by injury associated with cochlear implantation is deemed to be significant, as it may give rise to low-frequency residual hearing loss by interfering with the blood labyrinth barrier and neural synapses. Pathological changes along the pathway for low-frequency auditory signals transmission may include latent factors such as damage to neuroepithelial structures, synapses, stria vascularis and other ultrastructures. In this review, current research on mechanisms of low-frequency residual hearing loss after cochlear implantation and possible roles of inflammatory responses are summarized.

The benefits of preserving residual hearing following cochlear implantation: a systematic review

OBJECTIVE

Systematically review the current literature for evidence on the "real-life" benefits of hearing preservation cochlear implantation (HPCI) for children and adults.

DESIGN

Systematic search of Pubmed, MEDLINE, EMBASE, CINHAL and Cochrane Library for MesH terms hearing¸ preservation and cochlear implantation. Inclusion criteria were the "real-life" benefit of HPCI i.e. other than pre- and post-operative pure tone thresholds. Exclusion criteria were non-English language, conference abstracts, reviews and animal and cadaveric studies. Risk of bias was assessed using the Evidence Project Tool.

STUDY SAMPLE

37 studies that matched criteria for review with 8/37 including children and 29/37 including adults.

RESULTS

HPCI was associated with better speech perception in noise in 18/26 papers and better music perception in 4/5 papers. There was no significant benefit reported in speech perception in quiet (14/20 papers) or binaural cues (3/4 papers), nor was there convincing evidence of HPCI outperforming bimodal users (5/7 papers). QoL scores were high amongst HPCI patients (2/2 papers). Interpretation of findings was hindered by small study groups and significant heterogeneity in various parameters.

CONCLUSION

Current literature on the "real-life" benefit of HPCI, although limited, supports the existence of meaningful benefit, especially in speech perception in noise and music perception.

The Influence of Cochlear Implant-Based Electric Stimulation on the Electrophysiological Characteristics of Cultured Spiral Ganglion Neurons

Background

Cochlear implant-based electrical stimulation may be an important reason to induce the residual hearing loss after cochlear implantation. In our previous study, we found that charge-balanced biphasic electrical stimulation inhibited the neurite growth of spiral ganglion neurons (SGNs) and decreased Schwann cell density in vitro. In this study, we want to know whether cochlear implant-based electrical stimulation can induce the change of electrical activity in cultured SGNs.

Methods

Spiral ganglion neuron electrical stimulation in vitro model is established using the devices delivering cochlear implant-based electrical stimulation. After 48 h treatment by 50 μA or 100 μA electrical stimulation, the action potential (AP) and voltage depended calcium current (I Ca) of SGNs are recorded using whole-cell electrophysiological method.

Results

The results show that the I Ca of SGNs is decreased significantly in 50 μA and 100 μA electrical stimulation groups. The reversal potential of I Ca is nearly +80 mV in control SGN, but the reversal potential decreases to +50 mV in 50 μA and 100 μA electrical stimulation groups. Interestingly, the AP amplitude, the AP latency, and the AP duration of SGNs have no statistically significant differences in all three groups.

Conclusion

Our study suggests cochlear implant-based electrical stimulation only significantly inhibit the I Ca of cultured SGNs but has no effect on the firing of AP, and the relation of I Ca inhibition and SGN damage induced by electrical stimulation and its mechanism needs to be further studied.

Cochlear implants and other inner ear prostheses: today and tomorrow

Cochlear implants (CIs) are implantable auditory prostheses designed to restore access to sound in deaf individuals via direct electrical stimulation of the auditory nerve. While CIs have been successful in restoring speech perception to many deaf patients, outcomes are variable and speech recognition in noise remains a problem. This chapter will review the factors underlying this variability, and discuss significant recent innovations to address these issues including neural health preservation, characterization, and regeneration, and other inner ear prostheses. The emerging role of central auditory plasticity will also be discussed. Together, these advances will point to the likely future directions for advancing the next generation of CIs and other inner ear prostheses.

Opposite Roles of NT-3 and BDNF in Synaptic Remodeling of the Inner Ear Induced by Electrical Stimulation

With the development of neural prostheses, neural plasticity including synaptic remodeling under electrical stimulation is drawing more and more attention. Indeed, intracochlear electrical stimulation used to restore hearing in deaf can induce the loss of residual hearing and synapses of the inner hair cells (IHCs). However, the mechanism under this process is largely unknown. Considering that the guinea pig is always a suitable and convenient choice for the animal model of cochlea implant (CI), in the present study, normal-hearing guinea pigs were implanted with CIs. Four-hour electrical stimulation with the intensity of 6 dB above electrically evoked compound action potential (ECAP) threshold (which can decrease the quantity of IHC synapses and the excitability of the auditory nerve) resulted in the upregulation of Bdnf (p < 0.0001) and downregulation of Nt-3 (p < 0.05). Intracochlear perfusion of exogenous NT-3 or TrkC/Fc (which blocks NT-3) can, respectively, resist or aggravate the synaptic loss induced by electrical stimulation. In contrast, local delivery of exogenous BDNF or TrkB/Fc (which blocks BDNF) to the cochlea, respectively, exacerbated or protected against the synaptic loss caused by electrical stimulation. Notably, the synaptic changes were only observed in the basal and middle halves of the cochlea. All the findings above suggested that NT-3 and BDNF may play opposite roles in the remodeling of IHC synapses induced by intracochlear electrical stimulation, i.e. NT-3 and BDNF promoted the regeneration and degeneration of IHC synapses, respectively.

Electric-acoustic stimulation with longer electrodes for potential deterioration in low-frequency hearing

Background: Electric-acoustic stimulation (EAS) has emerged as a standard treatment for patients with high-frequency hearing loss. EAS is usually performed with shorter electrodes of 16-24 mm in length. As most EAS recipients gradually lose residual acoustic hearing in the implanted ear over time, EAS with longer electrodes without causing significant intra-cochlear damage might be ideal.Objective: The aim of this study was to investigate hearing preservation (HP) results after EAS surgery with longer electrodes.Methods: Ten patients (11 ears) with partial deafness that met the indications for EAS with a MED-EL FLEX28 electrode were included in this study. Auditory thresholds before and at 6 months after activation were examined.Results: In 100% of cases, HP was comfortably achieved, indicating that all patients could utilize acoustic amplification combined with electric stimulation.Conclusion: EAS with longer electrodes can offer broader cochlear coverage, resulting in natural frequency matching in comparison with shorter electrodes, even in EAS cases. The combination of advanced surgical techniques and flexible, long, straight electrodes permits deep insertion that reaches the apical region with little or no insertion trauma.

Acceptance and Benefits of Electro-Acoustic Stimulation for Conventional-Length Electrode Arrays

BACKGROUND

Prior studies have shown an advantage for electro-acoustic stimulation (EAS) in cochlear implant (CI) patients with residual hearing, but the degree of benefit can vary. The objective was to explore which factors relate to performance with and acceptance of EAS for CI users with conventional-length electrodes.

METHODS

A retrospective chart review was conducted for adults with an average threshold of 75 dB hearing loss or better across 250 and 500 Hz preoperatively (n = 83). All patients underwent cochlear implantation with a conventional-length electrode. Low-frequency audiometric thresholds were measured at initial activation as well as 3 and 12 months postoperatively to determine who met the criteria for EAS. Speech perception for CNC words and AzBio sentences in quiet and +10 dB SNR noise was evaluated 3 and 12 months after activation.

RESULTS

Speech perception in quiet and noise was similar regardless of whether or not the patient was eligible for EAS. Less than half of the patients who met the EAS criteria chose to use it, citing reasons such as physical discomfort or lack of perceived benefit. EAS users performed better on CNC words but not sentence recognition than EAS nonusers.

CONCLUSIONS

EAS use is dependent on audiologic and nonaudiologic issues. Hearing preservation is possible with conventional electrodes, but hearing preservation alone does not guarantee superior speech perception.

Mechanical Effects of Cochlear Implants on Residual Hearing Loss: A Finite Element Analysis

The effects of cochlear implants on residual hearing loss is investigated through a finite element model of human auditory periphery consisting of the cochlea and middle ear. The simulation results show that a round window stiffness is the dominant factor in residual hearing loss. The increased round window stiffness to five times caused over 4 dB residual hearing loss at low frequencies below 500 Hz. Without considering round window ossification, inserting a cochlear implant can show at most 4 dB difference of residual hearing loss in magnitude from the no-implant case although the cochlear implant's geometry and position has been varied. If the stiffness of the round window is the same, the simulation results suggest to use a thin-straight-cochlear implant inserted into the lateral side in order to preserve residual hearing at frequencies below 700 Hz. In addition, when the distance between the basilar membrane and a cochlear implant is closer, the residual hearing loss becomes severe at high frequencies above 1 kHz. The results would be helpful for choice of a cochlear implant depending on a patient's condition.

Long-term residual hearing in cochlear implanted adult patients who were candidates for electro-acoustic stimulation

PURPOSE

To evaluate the long-term hearing outcomes in cochlear implanted adults with residual hearing at low frequencies, and the proportion of patients using electro-acoustic stimulation (EAS).

METHODS

A monocentric retrospective cohort study was performed in a tertiary referral center. Population demographics, surgical approach, pre- and postoperative hearing at low frequencies, in the implanted and contralateral ear, were recorded as well as duration of EAS use. The percentage hearing preservation was calculated according to the formula S (HEARRING group).

RESULTS

In total, 63 adults (81 ears) with residual hearing underwent cochlear implantation with intent to use EAS processors. Six different types of electrode array were implanted. The mean pure tone audiometry (PTA) shift after cochlear implantation was 16 ± 15 dB HL (range 0-59 dB HL). Half of the implanted ears had minimal hearing preservation or total hearing loss (HL) at 5.5 years and the cumulative risk of total HL was 50% at 7 years. During the follow-up, total HL occurred in 22 ears. The decrease in hearing levels was similar in both implanted and contralateral ear during follow-up (ns, F = 2.46 ± 3, Linear Mixed Model (LMM)). Only 44 patients found a benefit from EAS at the first fitting. At the last visit, EAS processors were fitted in 30% of the cases. The pre- and postoperative mean PTA thresholds were not predictive of EAS use (Cox's proportional hazards analysis).

CONCLUSIONS

Postoperative residual hearing was observed in 93% of implanted ears, but only half of them had an initial benefit from EAS. No predictive factors were found to influence the use of EAS processors.

Electrical stimulation induces synaptic changes in the peripheral auditory system

Since a rapidly increasing number of neurostimulation devices are used clinically to modulate specific neural functions, the impact of electrical stimulation on targeted neural structure and function has become a key issue. In particular, the specific effect of electrical stimulation via a cochlear implant (CI) on inner hair cell (IHC) synapses remains unclear. Importantly, CI candidacy has recently expanded to include patients with partial hearing loss. Unfortunately, some CI recipients experience progressive hearing loss after activation of electrical stimulation. The mechanism(s) accounting for loss of residual hearing following electrical stimulation is unknown. Here normal-hearing guinea pigs were implanted with customized CIs. Intracochlear electrical stimulation with an intensity equal to or above electrically evoked compound action potential (ECAP) threshold decreased the excitability of auditory nerve. Furthermore, the number of synapses between IHCs and the afferent spiral ganglion neurons (SGNs) also decreased after electrical stimulation with higher intensities. However, no significant change was observed in the packing density and perikaryal area of SGNs as well as the quantity of hair cells. These results carry important implications for use of CIs in patients with residual hearing and for an increasing number of patients treated with other neurostimulation devices. Notably, the results were based on acute electrical stimulation. Considering the complex interaction between CIs and targeted tissues, it is urgent to conduct further research to clarify whether the similar changes could be induced by chronic electrical stimulation.

Long-term effects and potential limits of intratympanic dexamethasone-loaded hydrogels combined with dexamethasone-eluting cochlear electrodes in a low-insertion trauma Guinea pig model

Cochlear implantation has become the most effective hearing restoration method and is one of the great advances in modern medicine. Early implants have been continuously developed into more efficient devices, and electro-acoustic stimulation is increasingly expanding the indication criteria for cochlear implants to patients with more residual hearing. Therefore, protecting the cochlear structures and maintaining its intrinsic capacities like residual hearing has become more important than ever before. In the present study, we aimed to assess the long-term protective effects of a dexamethasone-eluting electrode combined with the preoperative intratympanic application of a dexamethasone-loaded thermoreversible hydrogel in a cochlear implant guinea pig model. 40 normal-hearing animals were equally randomized into a control group receiving an unloaded hydrogel and a non-eluting electrode, a group receiving a dexamethasone-loaded hydrogel and a non-eluting electrode, a group receiving an unloaded hydrogel and a dexamethasone-eluting electrode and a group receiving both a dexamethasone-loaded hydrogel and a dexamethasone-eluting electrode. Residual hearing and impedances were investigated during a period of 120 days. Tissue response and histological changes of cochlear structures were analyzed at the end of the experiments. Treatment with dexamethasone did not show a significant protective effect on residual hearing independent of treatment group. Although the majority of the cochleae didn't exhibit any signs of electrode insertion trauma, a small degree of tissue response could be observed in all animals without a significant difference between the groups. Foreign body giant cells and osteogenesis were significantly associated with tissue response. Hair cells, synapsin-1-positive cells and spiral ganglion cells were preserved in all study groups. Cochlear implantation using a dexamethasone-eluting electrode alone and in combination with a dexamethasone-loaded hydrogel significantly protected auditory nerve fibers on day 120. Post-implantation impedances were equal across study groups and remained stable over the duration of the experiment. In this study we were able to show that use of a dexamethasone-eluting electrode alone and in combination with preoperative application of dexamethasone-loaded hydrogel significantly protects auditory nerve fibers. Furthermore, we have shown that a cochlear implantation-associated hearing threshold shift and tissue response may not be completely prevented by the sole application of dexamethasone.

Electrical Stimulation Degenerated Cochlear Synapses Through Oxidative Stress in Neonatal Cochlear Explants

Neurostimulation devices use electrical stimulation (ES) to substitute, supplement or modulate neural function. However, the impact of ES on their modulating structures is largely unknown. For example, recipients of cochlear implants using electroacoustic stimulation experienced delayed loss of residual hearing over time after ES, even though ES had no impact on the morphology of hair cells. In this study, using a novel model of cochlear explant culture with charge-balanced biphasic ES, we found that ES did not change the quantity and morphology of hair cells but decreased the number of inner hair cell (IHC) synapses and the density of spiral ganglion neuron (SGN) peripheral fibers. Inhibiting calcium influx with voltage-dependent calcium channel (VDCC) blockers attenuated the loss of SGN peripheral fibers and IHC synapses induced by ES. ES increased ROS/RNS in cochlear explants, but the inhibition of calcium influx abolished this effect. Glutathione peroxidase 1 (GPx1) and GPx2 in cochlear explants decreased under ES and ebselen abolished this effect and attenuated the loss of SGN peripheral fibers. This finding demonstrated that ES induced the degeneration of SGN peripheral fibers and IHC synapses in a current intensity- and duration-dependent manner in vitro. Calcium influx resulting in oxidative stress played an important role in this process. Additionally, ebselen might be a potential protector of ES-induced cochlear synaptic degeneration.

Cochlear Implant Surgery Through Round Window Approach Is Always Possible

OBJECTIVES

The benefit of round window (RW) approach for cochlear implant (CI) has been well studied. Because the RW represents a natural door to scala tympani, it facilitates precise electrode insertion. Atraumatic electrode insertion can also be performed without drilling the cochlear lateral wall. However, the RW approach has several limitations. The purpose of this study is to describe successful CI surgeries utilizing the RW approach except for severe cases of temporal bone anomaly. The authors' successful surgical solution for cases involving difficult RW access is also described.

MATERIALS AND METHODS

We retrospectively analyzed 377 consecutive surgeries of cochlear implantation performed between June 2010 and December 2018 by a single experienced surgeon. Standard and alternative procedures were used according to anatomical variations. Standard procedures included modified techniques of mastoidectomy in the RW approach, opening of facial recess, exposure of RW membrane, and electrode insertion. Difficult cases involving severe rotated cochlea or hypoplastic mastoid were successfully treated with RW insertion using alternative procedures such as external auditory canal (EAC) wall mobilization and endomeatal approach.

RESULTS

We performed CI surgery through a reproducible RW technique in two cases involving endomeatal approach and three cases of EAC mobilization. Other cases were treated using the standard procedure.

CONCLUSION

Cochlear implant surgery through RW is reliable, safe, and effective. The RW technique is reproducible via several surgical procedures in most CI cases. Identification and safe exposure of RW membrane is a prerequisite for successful electrode insertion in cochlear implant surgery.

Exploration of factors influencing the preservation of residual hearing following cochlear implantation

BACKGROUND

 Increasing access to cochlear implants within the resource-constrained South African context calls for careful investigation of all factors that might influence benefit from this technological advancement.

OBJECTIVE

 The aim of this study was to investigate preservation of hearing following cochlear implant surgery and whether a relationship existed between the post-operative hearing findings and certain factors.

METHODS

 Within a quantitative paradigm, a retrospective data review design was adopted where a sample consisting of audiological records from 60 observations and surgical records from two cochlear implant units in South Africa was investigated. These records were selected using purposive sampling and consisted of records from participants ranging from 6 to 59 years. Comparative analysis of unaided audiological test results was pre- and post-operatively performed, where all paitents were implanted with cochlear devices. Factors documented to have a possible influence on post-operative outcomes were examined in an attempt to establish relationships that may exist. Findings were analysed by means of both inferential and descriptive statistics.

RESULTS

 The findings indicated 92% success rate in preservation of residual hearing. There was a direct correlation between surgical techniques, as well as cochlear implant type and the successful hearing findings, in the absence of surgical complications. Other factors explored did not have any negative effect on the hearing findings.

CONCLUSION

 The study findings suggest improved surgical outcomes with enhanced surgical techniques and advanced technology, with a clear negative impact of intraoperative complications on the outcomes.

Binaural interference with simulated electric acoustic stimulation

Preserved low-frequency acoustic hearing in cochlear implant (CI) recipients affords combined electric-acoustic stimulation (EAS) that could improve access to low-frequency acoustic binaural cues and enhance spatial hearing. Such benefits, however, could be undermined by interactions between electrical and acoustical inputs to adjacent (spectral overlap) or distant (binaural interference) cochlear places in EAS. This study simulated EAS in normal-hearing listeners, measuring interaural time difference (ITD) and interaural level difference (ILD) discrimination thresholds for a low-frequency noise (simulated acoustic target) in the presence or absence of a pulsatile high-frequency complex presented monotically or diotically (simulated unilateral or bilateral electric distractor). Unilateral distractors impaired thresholds for both cue types, suggesting influences of both binaural interference (which appeared more consistently for ITD than ILD) and physical spectral overlap (for both cue types). Reducing spectral overlap with an EAS gap between 1 and 3 kHz consistently improved binaural sensitivity. Finally, listeners displayed significantly lower thresholds with simulated bilateral versus unilateral electric stimulation. The combined effects revealed similar or better thresholds in bilateral full spectral overlap than in unilateral EAS gap conditions, suggesting that bilateral implantation with bilateral acoustic hearing preservation could allow for higher tolerance of spectral overlap in CI users and improved binaural sensitivity over unilateral EAS.

Cochlear implants: Insertion assessment by computed tomography

BACKGROUND AND OBJECTIVES

Imaging exams play a key role in cochlear implants with regard to both planning implantation before surgery and quality control after surgery. The ability to visualize the three-dimensional location of implanted electrodes is useful in clinical routines for assessing patient outcome. The aim of this study was to evaluate linear and angular insertion depth measurements of cochlear implants based on conventional computed tomography.

METHODS

Tools for linear and angular measurements of cochlear implants were used in computed tomography exams. The tools realized the insertion measurements in an image reconstruction of the CIs, based on image processing techniques. We comprehensively characterized two cochlear implant models while obviating possible changes that can be caused by different cochlea sizes by using the same human temporal bones to evaluate the implant models.

RESULTS

The tools used herein were able to differentiate the insertion measurements between two cochlear implant models widely used in clinical practice. We observed significant differences between both insertion measurements because of their different design and construction characteristics (p = 0.004 and 0.003 for linear and angular measurements, respectively; t-test). The presented methodology showed to be a good tool to calculate insertion depth measurements, since it is easy to perform, produces high-resolution images, and is able to depict all the landmarks, thus enabling measurement of the angular and linear insertion depth of the most apical electrode contacts.

CONCLUSION

The present study demonstrates practical and useful tools for evaluating cochlear implant electrodes in clinical practice. Further studies should measure preoperative and postoperative benefits in terms of speech recognition and evaluate the preservation of residual hearing in the implanted ear. Such studies can also determine correlations between surgical factors, electrode positions, and performance. In addition to refined surgical techniques, the precise evaluation of cochlear length and correct choice of cochlear implant characteristics can play an important role in postoperative outcomes.

Preliminary Outcomes Report for CO2 Laser Assisted Electric-Acoustic Cochlear Implantation

OBJECTIVE

Report on the safety/efficacy of a novel, carbon dioxide (CO2) laser-assisted protocol for hearing-preservation cochlear implantation (HPCI) and electric-acoustic stimulation (EAS).

STUDY DESIGN

Retrospective case review.

SETTING

Tertiary referral center.

PATIENTS

Adult patients meeting established criteria for HPCI and EAS.

INTERVENTION

Therapeutic/rehabilitative. A standardized protocol used CO2 laser to achieve meticulous hemostasis and perform cochleostomy was evaluated.

MAIN OUTCOME MEASURES

Audiometric assessments included low-tone pure tone average (LtPTA), consonant-nucleus-consonant (CNC), and AzBio scores. Primary outcomes were low-tone hearing-preservation (LtHP) and EAS usage rates. Secondary outcomes included change in LtPTA, outcomes durability, and the rate/onset/presentation of delayed hearing loss (DHL). Subset analyses stratified data by presenting LtPTA and surgeon experience.

RESULTS

Forty-seven patients and 52 ears were included. Mean follow-up was 20.7 ± 12.6 months. When adjusted for preoperative LtPTA less than 60 dB, the LtHP rate was 77%. This was significantly better than for patients with LtPTA more than 60 dB (24%; p < 0.0001). Outcomes were highly durable. EAS usage was excellent in those with LtPTA less than 60 dB (100%). Nine patients developed DHL. Three additional patients (25%) were successfully salvaged via steroids. Both CNC and AzBio scores improved significantly (p < 0.0001) at definitive testing. Speech-hearing scores did not differ significantly between patients using/not using EAS. The complication rate was 3.8%; none were caused by the laser. Surgeon experience was associated with significantly better outcomes.

CONCLUSION

Use of a CO2 laser-assisted HPCI protocol was safe and effective. Outcomes were consistent with contemporary literature reporting. Patient selection and surgeon experience both significantly impacted outcomes.

Cochlear volume as a predictive factor for residual-hearing preservation after conventional cochlear implantation

OBJECTIVE

The preservation of residual hearing after conventional cochlear implantation (CI) is frequently observed when atraumatic soft surgery is adopted. The purpose of this study was to elucidate the predictive factors for residual hearing preservation after atraumatic CI.

PATIENTS

This study included 46 patients who underwent CI based on an atraumatic technique using a standard-length flexible electrode implant through a round window approach.

MAIN OUTCOME MEASURE

Cochlear volume was measured using magnetic resonance imaging (MRI). Cochlear duct length (CDL) was taken as the length of the scala media measured using computed tomography (CT). The association between residual hearing preservation and cochlear volume/CDL was then examined.

RESULT

Cochlear volume and CDL were significantly larger in patients with complete hearing preservation than in those with hearing loss. Multivariate logistic regression analysis revealed that cochlear volume was a significant predictive factor for residual hearing preservation.

CONCLUSION

Residual hearing preservation after conventional CI was observed in patients with a larger cochlear volume and longer CDL. Cochlear volume could be a predictive factor for residual hearing preservation after conventional CI.

Preservation of residual hearing after cochlear implant surgery: an exploration of residual hearing function in a group of recipients at cochlear implant units

Introduction

The preservation of residual hearing is becoming increasingly important in cochlear implant surgery. Conserving residual hearing is a positive prognostic indicator for improved hearing abilities.

Objective

The primary aim of the study was to explore the preservation of residual hearing following cochlear implantation in a group of recipients at two major cochlear implant centers.

Methods

A quantitative paradigm was adopted and exploratory research conducted within a retrospective data review design. The sample consisted of 50 surgical records and 53 audiological records from 60 observations (53 patients, seven of whom were implanted bilaterally). The records were selected using purposive sampling and consisted of records from participants ranging from six to 59 years of age. The average time of when the postoperative audiograms were performed in the current study was 24.7 months (s.d. = ±9.0). Data were analyzed through both qualitative and inferential statistics and a comparative analysis of unaided pre- and postoperative audiological test results was conducted.

Results

Results indicated a high success rate of 92% preservation of residual hearing with half of the sample exhibiting complete preservation in cochlear implant recipients across all frequencies postoperatively. A total postoperative hearing loss was found in only 8% of cochlear implantees across all frequencies. There was no relationship between preoperative hearing thresholds and preservation of hearing postoperatively. The two main surgical techniques used in the current study were the contour on stylet and the advance off-stylet techniques, with the majority of surgeons utilizing a cochleostomy approach. From the findings, it became apparent that the majority of cases did not have any reported intraoperative complications. This is a positive prognostic indicator for the preservation of residual hearing.

Conclusion

Findings suggest improved cochlear implant surgical outcomes when compared to previous studies implying progress in surgical techniques. The surgical skill and experience of the surgeon are evidenced by the minimal intraoperative complications and the high success rate of hearing preservation. This is a positive prognostic indicator for individuals with preoperative residual hearing as the preserved residual hearing allows for the potential of electro-acoustic stimulation, which in turn has its own hearing benefits.

Hearing Preservation: Does Electrode Choice Matter?

Objective Evaluate if electrode design affects hearing preservation (HP) following cochlear implantation (CI) with full-length electrodes. Study Design Case series with chart review. Setting Tertiary referral academic center. Subjects and Methods Forty-five adults with low-frequency hearing (≤85 dB at 250 and 500 Hz) who underwent unilateral CI with full-length electrode arrays made by 1 manufacturer were included. HP was calculated with (1) mean low-frequency pure-tone average (LFPTA) at 250 and 500 Hz (MEAN method), (2) a percentile method across the audiometric frequency spectrum generating an S-value (HEARRING method), and (3) functional if hearing remained ≤85 dB at 250 and 500 Hz. Audiometric testing was performed approximately 1 month and 1 year postoperatively, yielding short-term and long-term results, respectively. Results Of 45 patients who underwent CI, 46.7% received lateral wall (LW) and 53.3% received perimodiolar (PM) electrodes. At short-term follow-up, LW electrodes were associated with significantly better HP than PM (LFPTA method: 27.7 vs 39.3 dB, P < .05; S-value method: 48.2 vs 21.8%, P < .05). In multivariate regression of short-term outcomes, LW electrode use was a significant predictor of better HP ( P < .05). At long-term follow-up, electrode type was not associated with HP. Younger patient age was the only significant predictor of long-term HP on multivariate analysis ( P < .05). Conclusion The LW electrode is associated with short-term HP, suggesting its design is favorable for limiting trauma to the cochlea during and directly following CI. Other factors, including age, are relevant for maintaining HP over the long term. The data support further investigation into what modifiable factors may promote long-term HP.

Long-term results of hearing preservation cochlear implant surgery in patients with residual low frequency hearing

CONCLUSION

Differences were found between patients with stable hearing and those with progressive hearing loss in the lower frequencies with respect to the rate of progression in the contralateral ear. It is suggested that the electric acoustic stimulation (EAS) can provide improvement in hearing ability over the long-term if residual hearing might be lost to some extent.

OBJECTIVE

To evaluate the long-term threshold changes in the low frequency hearing of the implanted ear as compared with the non-implanted ear, and the hearing abilities with EAS along with the extent of residual hearing.

METHODS

Seventeen individuals were enrolled and received the EAS implant with a 24-mm FLEXeas electrode array. Hearing thresholds and speech perception were measured pre- and post-operatively for 1-5 years. Post-operative hearing preservation (HP) rates were calculated using the preservation numerical scale.

RESULTS

The average linear regression coefficient for the decline in hearing preservation score was -6.9 for the implanted ear and the patients were subsequently categorized into two groups: those with better than average, stable hearing; and those with worse than average, progressive hearing loss. EAS showed better results than electric stimulation alone, in spite of an absence of speech perception with acoustic stimulation.

Intracochlear Pressure Transients During Cochlear Implant Electrode Insertion

HYPOTHESIS

Cochlear implant (CI) electrode insertion into the round window induces pressure transients in the cochlear fluid comparable to high-intensity sound transients.

BACKGROUND

Many patients receiving a CI have some remaining functional hearing at low frequencies; thus, devices and surgical techniques have been developed to use this residual hearing. To maintain functional acoustic hearing, it is important to retain function of any hair cells and auditory nerve fibers innervating the basilar membrane; however, in a subset of patients, residual low-frequency hearing is lost after CI insertion. Here, we test the hypothesis that transient intracochlear pressure spikes are generated during CI electrode insertion, which could cause damage and compromise residual hearing.

METHODS

Human cadaveric temporal bones were prepared with an extended facial recess. Pressures in the scala vestibuli and tympani were measured with fiber-optic pressure sensors inserted into the cochlea near the oval and round windows, whereas CI electrodes (five styles from two manufacturers) were inserted into the cochlea via a round window approach.

RESULTS

Pressures in the scala tympani tended to be larger in magnitude than pressures in the scala vestibuli, consistent with electrode insertion into the scala tympani. CI electrode insertion produced a range of pressure transients in the cochlea that could occur alone or as part of a train of spikes with equivalent peak sound pressure levels in excess of 170 dB sound pressure level. Instances of pressure transients varied with electrode styles.

CONCLUSION

Results suggest electrode design, insertion mechanism, and surgical technique affect the magnitude and rate of intracochlear pressure transients during CI electrode insertion. Pressure transients showed intensities similar to those elicited by high-level sounds and thus could cause damage to the basilar membrane and/or hair cells.