Quantitative evaluation of new bone and fibrous tissue in the cochlea following cochlear implantation in the human

Human Histology after Structure Preservation Cochlear Implantation via Round Window Insertion

OBJECTIVES

Current surgical techniques aim to preserve intracochlear structures during cochlear implant (CI) insertion to maintain residual cochlear function. The optimal technique to minimize damage, however, is still under debate. The aim of this study is to histologically compare insertional trauma and intracochlear tissue formation in humans with a CI implanted via different insertion techniques.

METHODS

One recent temporal bone from a donor who underwent implantation of a full-length CI (576°) via round window (RW) insertion was compared with nine cases implanted via cochleostomy (CO) or extended round window (ERW) approach. Insertional trauma was assessed on H&E-stained histological sections. 3D reconstructions were generated and virtually re-sectioned to measure intracochlear volumes of fibrosis and neo-ossification.

RESULTS

The RW insertion case showed electrode translocation via the spiral ligament. 2/9 CO/ERW cases showed no insertional trauma. The total volume of the cochlea occupied by fibro-osseous tissue was 10.8% in the RW case compared with a mean of 30.6% (range 8.7%-44.8%, N = 9) in the CO/ERW cases. The difference in tissue formation in the basal 5 mm of scala tympani, however, was even more pronounced when the RW case (12.3%) was compared with the cases with a CO/ERW approach (mean of 93.8%, range 81% to 100%, N = 9).

CONCLUSIONS

Full-length CI insertions via the RW can be minimally traumatic at the cochlear base without inducing extensive fibro-osseous tissue formation locally. The current study further supports the hypothesis that drilling of the cochleostomy with damage to the endosteum incites a local tissue reaction.

LEVEL OF EVIDENCE

4: Case-control study Laryngoscope, 134:945-953, 2024.

The cochlear matrisome: Importance in hearing and deafness

The extracellular matrix (ECM) consists in a complex meshwork of collagens, glycoproteins, and proteoglycans, which serves a scaffolding function and provides viscoelastic properties to the tissues. ECM acts as a biomechanical support, and actively participates in cell signaling to induce tissular changes in response to environmental forces and soluble cues. Given the remarkable complexity of the inner ear architecture, its exquisite structure-function relationship, and the importance of vibration-induced stimulation of its sensory cells, ECM is instrumental to hearing. Many factors of the matrisome are involved in cochlea development, function and maintenance, as evidenced by the variety of ECM proteins associated with hereditary deafness. This review describes the structural and functional ECM components in the auditory organ and how they are modulated over time and following injury.

Osteoneogenesis at the Round Window: A Possible Cause of Cochlear Implant Failure?

Surgery for cochlear implant is a traumatic procedure, with inflammatory responses leading to immediate and delayed intracochlear changes, resulting in newly formed fibrous and bony tissue. This newly formed tissue is thought to affect speech perception with cochlear implants and can also play a role in causing device malfunctioning and soft failures. We present a case of left cochlear implant explantation and reimplantation in a 15-year-old girl, who experienced deterioration of speech perception and device failure associated with osteoneogenesis of the round window, which could represent a cause of cochlear implant failure. To avoid surgical trauma of the cochlear lateral wall, enlarged round window insertion rather than a cochleostomy, soft surgical techniques, and the application of steroids are all important issues to prevent new tissue formation, although special attention should also be given to the trauma of round window borders.

Impedance development after implantation of hybrid-L24 cochlear implant electrodes

OBJECTIVE

Shorter and thinner electrodes were developed for preserving residual hearing after cochlear implantation by minimising trauma. As trauma is regarded as one of the causes of fibrous tissue formation after implantation, and increase in impedance is considered to be connected to fibrous tissue formation, the aim of the current study was to evaluate impedance development after implantation of Hybrid-L electrodes.

DESIGN

Impedance values were retrospectively collected from our clinical database and evaluated for all active contacts and basal, middle and apical contacts separately for up to 10 years.

STUDY SAMPLES

All 137 adult patients received a Hybrid-L electrode and had to be implanted for at least 1 year.

RESULTS

On average impedances increased to 13 kOhm before first fitting and dropped to 5-7 kOhm under electrical stimulation with lower values measured on apical contacts. Mean values remained stable over years, but variability increased. Values before first fitting were independent of age at implantation whereas lower values were found later in patients of higher age at implantation.

CONCLUSION

Despite smaller contacts, impedance values after start of electrical stimulation were comparable to published values of Contour electrodes. This might suggest less tissue growth with the Hybrid-L electrode array.

A Multicenter Comparison of 1-yr Functional Outcomes and Programming Differences Between the Advanced Bionics Mid-Scala and SlimJ Electrode Arrays

OBJECTIVE

To determine if there is a difference in hearing outcomes or stimulation levels between Advanced Bionics straight and precurved arrays.

STUDY DESIGN

Retrospective chart review across three implant centers.

SETTING

Tertiary centers for cochlear and auditory brainstem implantation.

PATIENTS

One hundred fifteen pediatric and 205 adult cochlear implants (CIs) were reviewed. All patients were implanted under the National Institute for Health and Care Excellence 2009 guidelines with a HiRes Ultra SlimJ or Mid-Scala electrode array.

MAIN OUTCOME MEASURES

Hearing preservation after implantation, as well as CI-only listening scores for Bamford-Kowal-Bench sentences were compared 1 year after implantation. Stimulation levels for threshold and comfort levels were also compared 1 year after implantation.

RESULTS

Hearing preservation was significantly better with the SlimJ compared with the Mid-Scala electrode array. Bamford-Kowal-Bench outcomes were not significantly different between the two arrays in any listening condition. Stimulation levels were not different between arrays but did vary across electrode contacts. At least one electrode was deactivated in 33% of implants but was more common for the SlimJ device.

CONCLUSION

Modern straight and precurved arrays from Advanced Bionics did not differ in hearing performance or current requirements. Although hearing preservation was possible with both devices, the SlimJ array would still be the preferred electrode in cases where hearing preservation was a priority. Unfortunately, the SlimJ device was also prone to poor sound perception on basal electrodes. Further investigation is needed to determine if deactivated electrodes are associated with electrode position/migration, and if programming changes are needed to optimize the use of these high-frequency channels.

Objective Assessment of Perilymphatic Fistula in Cases of Postoperative Vertigo after Cochlear Implantation by Cochlin Tomoprotein (CTP)

OBJECTIVE

Vertigo is a quite frequent complication after cochlear implantation. Perilymphatic fistula (PLF) is assumed to be one cause of this problem. Cochlin tomoprotein (CTP) is a newly introduced marker for PLF. The present aim was to evaluate the rate of positive CTP testing in cases of newly occurring vertigo after cochlear implantation.

MATERIALS AND METHODS

Twelve patients with vertigo after cochlear implantation and a revisional electrode-sealing procedure underwent intraoperative rinsing of their middle ear. The sample was evaluated for CTP with monoclonal antibody testing. Sixteen controls from six CI patients were taken.

RESULTS

4 out of 12 (33%) cases showed positive CTP testing, indicating that a PLF could be evaluated. In all of the positive CTP cases, surgery decreased the vertigo symptoms. A relation between the subjective visual assessment of a fistula and a positive CTP value was not observed. Controls confirmed the value of the testing.

DISCUSSION

CTP detection objectively shows that PLF can occur in patients with vertigo after CI.

Tissue-Engineered Cochlear Fibrosis Model Links Complex Impedance to Fibrosis Formation for Cochlear Implant Patients

Cochlear implants are a life-changing technology for those with severe sensorineural hearing loss, partially restoring hearing through direct electrical stimulation of the auditory nerve. However, they are known to elicit an immune response resulting in fibrotic tissue formation in the cochlea that is linked to residual hearing loss and suboptimal outcomes. Intracochlear fibrosis is difficult to track without postmortem histology, and no specific electrical marker for fibrosis exists. In this study, a tissue-engineered model of cochlear fibrosis is developed following implant placement to examine the electrical characteristics associated with fibrotic tissue formation around electrodes. The model is characterized using electrochemical impedance spectroscopy and an increase in the resistance and a decrease in capacitance of the tissue using a representative circuit are found. This result informs a new marker of fibrosis progression over time that is extractable from voltage waveform responses, which can be directly measured in cochlear implant patients. This marker is tested in a small sample size of recently implanted cochlear implant patients, showing a significant increase over two postoperative timepoints. Using this system, complex impedance is demonstrated as a marker of fibrosis progression that is directly measurable from cochlear implants to enable real-time tracking of fibrosis formation in patients, creating opportunities for earlier treatment intervention to improve cochlear implant efficacy.

Using x-ray micro computed tomography to quantify intracochlear fibrosis after cochlear implantation in a Guinea pig model

Cochlear implants (CIs) allow individuals with profound hearing loss to understand speech and perceive sounds. However, not all patients obtain the full benefits that CIs can provide and the cause of this disparity is not fully understood. One possible factor for the variability in outcomes after cochlear implantation, is the development of fibrotic scar tissue around the implanted electrode. It has been hypothesised that limiting the extent of fibrosis after implantation may improve overall CI function, and longevity of the device. Currently, histology is often used to quantify the extent of intracochlear tissue growth after implantation however this method is labour intensive, time-consuming, often involves significant user bias, and causes physical distortion of the fibrosis. Therefore, this study aimed to evaluate x-ray micro computed tomography (μCT) as a method to measure the amount and distribution of fibrosis in a guinea pig model of cochlear implantation. Adult guinea pigs were implanted with an inactive electrode, and cochleae harvested eight weeks later (n = 7) and analysed using μCT, to quantify the extent of tissue reaction, followed by histological analysis to confirm that the tissue was indeed fibrotic. Cochleae harvested from an additional six animals following implantation were analysed by μCT, before and after contrast staining with osmium tetroxide (OsO4), to enhance the visualisation of soft tissues within the cochlea, including the tissue reaction. Independent analysis by two observers showed that the quantification method was robust and provided additional information on the distribution of the response within the cochlea. Histological analysis revealed that μCT visualised dense collagenous material and new bone formation but did not capture loose, areolar fibrotic tissue. Treatment with OsO4 significantly enhanced the visible tissue reaction detected using μCT. Overall, μCT is an alternative and reliable method that can be used to quantify the extent of the CI-induced intracochlear tissue response and will be a useful tool for the in vivo assessment of novel anti-fibrotic treatments.

Cochlear implantation impairs intracochlear microcirculation and counteracts iNOS induction in guinea pigs

Introduction

Preservation of residual hearing remains a great challenge during cochlear implantation. Cochlear implant (CI) electrode array insertion induces changes in the microvasculature as well as nitric oxide (NO)-dependent vessel dysfunction which have been identified as possible mediators of residual hearing loss after cochlear implantation.

Methods

A total of 24 guinea pigs were randomized to receive either a CI (n = 12) or a sham procedure (sham) by performing a cochleostomy without electrode array insertion (n = 12). The hearing threshold was determined using frequency-specific compound action potentials. To gain visual access to the stria vascularis, a microscopic window was created in the osseous cochlear lateral wall. Cochlear blood flow (CBF) and cochlear microvascular permeability (CMP) were evaluated immediately after treatment, as well as after 1 and 2 h, respectively. Finally, cochleae were resected for subsequent immunohistochemical analysis of the iNOS expression.

Results

The sham control group showed no change in mean CBF after 1 h (104.2 ± 0.7%) and 2 h (100.8 ± 3.6%) compared to baseline. In contrast, cochlear implantation resulted in a significant continuous decrease in CBF after 1 h (78.8 ± 8.1%, p < 0.001) and 2 h (60.6 ± 11.3%, p < 0.001). Additionally, the CI group exhibited a significantly increased CMP (+44.9% compared to baseline, p < 0.0001) and a significant increase in median hearing threshold (20.4 vs. 2.5 dB SPL, p = 0.0009) compared to sham after 2 h. Intriguingly, the CI group showed significantly lower iNOS-expression levels in the organ of Corti (329.5 vs. 54.33 AU, p = 0.0003), stria vascularis (596.7 vs. 48.51 AU, p < 0.0001), interdental cells (564.0 vs. 109.1 AU, p = 0.0003) and limbus fibrocytes (119.4 vs. 18.69 AU, p = 0.0286).

Conclusion

Mechanical and NO-dependent microvascular dysfunction seem to play a pivotal role in residual hearing loss after CI electrode array insertion. This may be facilitated by the implantation associated decrease in iNOS expression. Therefore, stabilization of cochlear microcirculation could be a therapeutic strategy to preserve residual hearing.

A new paradigm of hearing loss and preservation with cochlear implants: Learnings from fundamental studies and clinical research

In 2010 Cochlear initiated a coordinated preclinical research program to identify the factors and underlying mechanisms of acoustic hearing loss following cochlear implantation and device use. At its inception the program was structured around several major hypotheses implicated in the loss of acoustic hearing. The understanding of causes evolved over the course of the program, leading to an increased appreciation of the role of the biological response in post-implant hearing loss. A systematic approach was developed which mapped the cochlear implant journey along a timeline that considers all events in an individual's hearing history. By evaluating the available data in this context, rather than by discrete hypothesis testing, causative and associated factors may be more readily detected. This approach presents opportunities for more effective research management and may aid in identifying new prospects for intervention. Many of the outcomes of the research program apply beyond preservation of acoustic hearing to factors important to overall cochlear health and considerations for future therapies.

Dual Drug Delivery in Cochlear Implants: In Vivo Study of Dexamethasone Combined with Diclofenac or Immunophilin Inhibitor MM284 in Guinea Pigs

Cochlear implants are well established to treat severe hearing impairments. Despite many different approaches to reduce the formation of connective tissue after electrode insertion and to keep electrical impedances low, results are not yet satisfying. Therefore, the aim of the current study was to combine the incorporation of 5% dexamethasone in the silicone body of the electrode array with an additional polymeric coating releasing diclofenac or the immunophilin inhibitor MM284, some anti-inflammatory substances not yet tested in the inner ear. Guinea pigs were implanted for four weeks and hearing thresholds were determined before implantation and after the observation time. Impedances were monitored over time and, finally, connective tissue and the survival of spiral ganglion neurons (SGNs) were quantified. Impedances increased in all groups to a similar extent but this increase was delayed in the groups with an additional release of diclofenac or MM284. Using Poly-L-lactide (PLLA)-coated electrodes, the damage caused during insertion was much higher than without the coating. Only in these groups, connective tissue could extend to the apex of the cochlea. Despite this, numbers of SGNs were only reduced in PLLA and PLLA plus diclofenac groups. Even though the polymeric coating was not flexible enough, MM284 seems to especially have potential for further evaluation in connection with cochlear implantation.

Toward neural health measurements for cochlear implantation: The relationship among electrode positioning, the electrically evoked action potential, impedances and behavioral stimulation levels

Introduction

Estimating differences in neural health across different sites within the individual cochlea potentially enables clinical applications for subjects with a cochlear implant. The electrically evoked compound action potential (ECAP) is a measure of neural excitability that possibly provides an indication of a neural condition. There are many factors, however, that affect this measure and increase the uncertainty of its interpretation. To better characterize the ECAP response, its relationship with electrode positioning, impedances, and behavioral stimulation levels was explored.

Methods

A total of 14 adult subjects implanted with an Advanced Bionics cochlear electrode array were prospectively followed up from surgery to 6 months postoperative. Insertion depth, distance to the modiolus, and distance to the medial wall were assessed for each electrode by postoperative CT analysis. ECAPs were measured intraoperatively and at three visits postoperatively on all 16 electrodes using the NRI feature of clinical programming software and characterized using multiple parameters. Impedances and behavioral stimulation levels were measured at every fitting session.

Results

Patterns in ECAPs and impedances were consistent over time, but high variability existed among subjects and between different positions in the cochlea. Electrodes located closer to the apex of the cochlea and closer to the modiolus generally showed higher neural excitation and higher impedances. Maximum loudness comfort levels were correlated strongly with the level of current needed to elicit a response of 100 μV ECAP.

Conclusion

Multiple factors contribute to the ECAP response in subjects with a cochlear implant. Further research might address whether the ECAP parameters used in this study will benefit clinical electrode fitting or the assessment of auditory neuron integrity.

A Steadier Hand: The First Human Clinical Trial of a Single-Use Robotic-Assisted Surgical Device for Cochlear Implant Electrode Array Insertion

OBJECTIVE

To evaluate the safety and utility of an investigational robotic-assisted cochlear implant insertion system.

STUDY DESIGN

Prospective, single-arm, open-label study under abbreviated Investigational Device Exemption requirements.

SETTING

All procedures were performed, and all data were collected, at a single tertiary referral center.

PATIENTS

Twenty-one postlingually deafened adult subjects that met Food and Drug Administration indication criteria for cochlear implantation.

INTERVENTION

All patients underwent standard-of-care surgery for unilateral cochlear implantation with the addition of a single-use robotic-assisted insertion device during cochlear electrode insertion.

MAIN OUTCOME MEASURES

Successful insertion of cochlear implant electrode array, electrode array insertion time, postoperative implant function.

RESULTS

Successful robotic-assisted insertion of lateral wall cochlear implant electrode arrays was achieved in 20 (95.2%) of 21 patients. One insertion was unable to be achieved by either robotic-assisted or manual insertion methods, and the patient was retrospectively found to have a preexisting cochlear fracture. Mean intracochlear electrode array insertion time was 3 minutes 15 seconds. All implants with successful robotic-assisted electrode array insertion (n = 20) had normal impedance and neural response telemetry measures for up to 6 months after surgery.

CONCLUSIONS

Here we report the first human trial of a single-use robotic-assisted surgical device for cochlear implant electrode array insertion. This device successfully and safely inserted lateral wall cochlear implant electrode arrays from the three device manufacturers with devices approved but he Food and Drug Administration.

In vitro impact of platinum nanoparticles on inner ear related cell culture models

So far, it was supposed that the increase of electrical impedance following cochlear implant (CI) insertion was due to technical defects of the electrode, inflammatory and/or formation of scar tissue along the electrode. However, it was recently reported that corrosion of the platinum electrode contacts may be the reason for high impedances. It could be shown that platinum particles were stripped from the electrode surfaces. Its potential cytotoxic effects within the inner ear remains to be examined. In this study in vitro cell culture models of the mouse organ of Corti cell line (HEI-OC1) and the spiral ganglion (SG) cells derived from the cochleae neonatal rats were used to investigate the effects of the polyvinylpyrrolidone coated platinum nanoparticles (Pt-NPPVP, 3 nm) on cell metabolism, neuronal survival and neurite outgrowth. Our data revealed no decrease of the metabolic activity of the HEI-OC1 cells at Pt-NPPVP concentrations between 50-150 μg/ml. Also, staining with Calcein AM/EthD demonstrated prevalent presence of vital cells. As shown by transmission electron microscopy no Pt-NPPVP could be found at the cell surface or in the cytosol of the HEI-OC1 cells. Similarly, the SG cells exposed to 20-100 μg/ml Pt-NPPVP did not show any reduced survival rate and neurite outgrowth following staining of the neurofilament antigen even at the highest Pt-NPPVP concentration. Although the SG cells were exposed to Pt-NPPVP for further 72 h and 96 h immunocytochemical staining of the glial cells and fibroblasts presented normal cell morphology and growth independently of the cultivation period. Our data indicates that the used Pt-NPPVP do not trigger the cellular uptake and, thus, presumable do not initiate apoptotic pathways in cells of the organ of Corti cell line or the auditory nerve. The protection mechanisms to the Pt-NPPVP interactions remain to be clarified.

Extracellular Vesicles in Inner Ear Therapies-Pathophysiological, Manufacturing, and Clinical Considerations

(1) Background: Sensorineural hearing loss is a common and debilitating condition. To date, comprehensive pharmacologic interventions are not available. The complex and diverse molecular pathology that underlies hearing loss may limit our ability to intervene with small molecules. The current review foccusses on the potential for the use of extracellular vesicles in neurotology. (2) Methods: Narrative literature review. (3) Results: Extracellular vesicles provide an opportunity to modulate a wide range of pathologic and physiologic pathways and can be manufactured under GMP conditions allowing for their application in the human inner ear. The role of inflammation in hearing loss with a focus on cochlear implantation is shown. How extracellular vesicles may provide a therapeutic option for complex inflammatory disorders of the inner ear is discussed. Additionally, manufacturing and regulatory issues that need to be addressed to develop EVs as advanced therapy medicinal product for use in the inner ear are outlined. (4) Conclusion: Given the complexities of inner ear injury, novel therapeutics such as extracellular vesicles could provide a means to modulate inflammation, stress pathways and apoptosis in the inner ear.

A PLLA Coating Does Not Affect the Insertion Pressure or Frictional Behavior of a CI Electrode Array at Higher Insertion Speeds

To prevent endocochlear insertion trauma, the development of drug delivery coatings in the field of CI electrodes has become an increasing focus of research. However, so far, the effect of a polymer coating of PLLA on the mechanical properties, such as the insertion pressure and friction of an electrode array, has not been investigated. In this study, the insertion pressure of a PLLA-coated, 31.5-mm long standard electrode array was examined during placement in a linear cochlear model. Additionally, the friction coefficients between a PLLA-coated electrode array and a tissue simulating the endocochlear lining were acquired. All data were obtained at different insertion speeds (0.1, 0.5, 1.0, 1.5, and 2.0 mm/s) and compared with those of an uncoated electrode array. It was shown that both the maximum insertion pressure generated in the linear model and the friction coefficient of the PLLA-coated electrode did not depend on the insertion speed. At higher insertion speeds above 1.0 mm/s, the insertion pressure (1.268 ± 0.032 mmHg) and the friction coefficient (0.40 ± 0.15) of the coated electrode array were similar to those of an uncoated array (1.252 ± 0.034 mmHg and 0.36 ± 0.15). The present study reveals that a PLLA coating on cochlear electrode arrays has a negligible effect on the electrode array insertion pressure and the friction when higher insertion speeds are used compared with an uncoated electrode array. Therefore, PLLA is a suitable material to be used as a coating for CI electrode arrays and can be considered for a potential drug delivery system.

Cochlear implant explantation: An in vitro model to evaluate electrode explant force and trauma

OBJECTIVES

Removal of a cochlear implant and its intracochlear electrode array is sometimes necessary, potentially causing cochlear explant trauma. Explantation typically occurs years post-implantation by which time reactive tissue has formed around the electrode. We aimed to create an in-vitro electrode explant model to examine explant forces and intracochlear trauma across multiple electrode types and insertion depths.

STUDY DESIGN

An in-vitro model using gel to represent tissue surrounding the electrode was developed. Pre-curved electrodes and straight electrodes at different insertion depths (20mm, 25mm, 28mm) were explanted from the model. During explantation, explant force was measured, and high-definition videos were recorded to capture electrode exit path and gel disruption.

RESULTS

Explant force patterns varied based on electrode position in the scala tympani. Explant forces did not correlate with gel disruption, which represented explant trauma. The least gel disruption occurred with pre-curved electrodes and the under-inserted straight electrode. The greatest disruption occurred with the overly inserted straight electrode.

CONCLUSION

An in-vitro model using gel to mimic tissue surrounding the electrode may provide insights into potential electrode explant trauma. Explant force did not correlate with explant trauma in our model. Pre-curved electrodes and shallower insertion depth of a straight electrode resulted in the least amount of explant trauma.

PLLA Coating of Active Implants for Dual Drug Release

Cochlear implants, like other active implants, rely on precise and effective electrical stimulation of the target tissue but become encapsulated by different amounts of fibrous tissue. The current study aimed at the development of a dual drug release from a PLLA coating and from the bulk material to address short-term and long-lasting release of anti-inflammatory drugs. Inner-ear cytocompatibility of drugs was studied in vitro. A PLLA coating (containing diclofenac) of medical-grade silicone (containing 5% dexamethasone) was developed and release profiles were determined. The influence of different coating thicknesses (2.5, 5 and 10 µm) and loadings (10% and 20% diclofenac) on impedances of electrical contacts were measured with and without pulsatile electrical stimulation. Diclofenac can be applied to the inner ear at concentrations of or below 4 × 10⁻⁵ mol/L. Release of dexamethasone from the silicone is diminished by surface coating but not blocked. Addition of 20% diclofenac enhances the dexamethasone release again. All PLLA coatings serve as insulator. This can be overcome by using removable masking on the contacts during the coating process. Dual drug release with different kinetics can be realized by adding drug-loaded coatings to drug-loaded silicone arrays without compromising electrical stimulation.

Ultra-High-Resolution CT to Detect Intracochlear New Bone Formation after Cochlear Implantation

Background Histopathologic studies reported that cochlear implantation, a well-established means to treat severe-to-profound sensorineural hearing loss, may induce inflammation, fibrosis, and new bone formation (NBF) with possible impact on loss of residual hearing and hearing outcome. Purpose To assess NBF in vivo after cochlear implantation with ultra-high-spatial-resolution (UHSR) CT and its implication on long-term residual hearing outcome. Materials and Methods In a secondary analysis of a prospective single-center cross-sectional study, conducted between December 2016 and January 2018, patients with at least 1 year of cochlear implantation experience underwent temporal bone UHSR CT and residual hearing assessment. Two observers evaluated the presence and location of NBF independently, and tetrachoric correlations were used to assess interobserver reliability. In addition, the scalar location of each electrode was assessed. After consensus agreement, participants were classified into two groups: those with NBF (n = 83) and those without NBF (n = 40). The association between NBF and clinical parameters, including electrode design, surgical approach, and long-term residual hearing loss, was tested using the χ² and Student t tests. Results A total of 123 participants (mean age ± standard deviation, 63 years ± 13; 63 women) were enrolled. NBF was found in 83 of the 123 participants (68%) at 466 of 2706 electrode contacts (17%). Most NBFs (428 of 466, 92%) were found around the 10 most basal contacts, with an interobserver agreement of 86% (2297 of 2683 contacts). Associations between electrode types and surgical approaches were significant (58 of 79 participants with NBF and a precurved electrode vs 24 of 43 with NBF and a straight electrode, P = .04; 64 of 88 participants with NBF and a cochleostomy approach vs 18 of 34 with NBF and a round window approach, P = .03). NBF was least often seen in full scala tympani insertions, but there was no significant association between scalar position and NBF (P = .15). Long-term residual hearing loss was significantly larger in the group with NBF compared with the group without NBF (mean, 22.9 dB ± 14 vs 8.6 dB ± 18, respectively; P = .04). Conclusion In vivo detection of new bone formation (NBF) after cochlear implantation is possible by using ultra-high-spatial-resolution CT. Most cochlear implant recipients develop NBF, predominately located at the base of the cochlea. NBF adversely affects long-term residual hearing preservation. © RSNA, 2021.

Predictors of Fibrotic and Bone Tissue Formation With 3-D Reconstructions of Post-implantation Human Temporal Bones

HYPOTHESIS

Years of implantation, surgical insertion approach, and electrode length will impact the volume of new tissue formation secondary to cochlear implantation.

BACKGROUND

New tissue formation, fibrosis, and osteoneogenesis after cochlear implantation have been implicated in increasing impedance and affecting performance of the cochlear implant.

METHODS

3-D reconstructions of 15 archival human temporal bones from patients with a history of cochlear implantation (CI) were generated from H&E histopathologic slides to study factors which affect volume of tissue formation.

RESULTS

Years of implantation was a predictor of osteoneogenesis (r = 0.638, p-value = 0.011) and total new tissue formation (r = 0.588, p-value = 0.021), however not of fibrosis (r = 0.235, p-value = 0.399). Median total tissue formation differed between cochleostomy and round window insertions, 25.98 and 10.34%, respectively (Mann-Whitney U = 7, p = 0.018). No correlations were found between electrode length or angular insertion depth and total new tissue (p = 0.192, p = 0.35), osteoneogenesis (p = 0.193, p = 0.27), and fibrosis (p = 0.498, p = 0.83), respectively. However, the type II error for electrode length and angular insertion depth ranged from 0.73 to 0.90, largely due to small numbers of the shorter electrodes.

CONCLUSIONS

With numbers of cochlear implant recipients increasing worldwide, an understanding of how to minimize intracochlear changes from implantation is important. The present study demonstrates that increasing years of implantation and inserting electrodes via a cochleostomy compared with a round window approach are associated with significantly greater degree of new tissue volume formation. While previous studies have demonstrated increased intracochlear damage in the setting of translocation with longer electrodes, length, and angular insertion depth of CI electrodes were not associated with increased tissue formation.

Effect of Cochlear Implantation on Vestibular Evoked Myogenic Potentials and Wideband Acoustic Immittance

OBJECTIVES

The objective of this study was to determine if absent air conduction stimuli vestibular evoked myogenic potential (VEMP) responses found in ears after cochlear implantation can be the result of alterations in peripheral auditory mechanics rather than vestibular loss. Peripheral mechanical changes were investigated by comparing the response rates of air and bone conduction VEMPs as well as by measuring and evaluating wideband acoustic immittance (WAI) responses in ears with cochlear implants and normal-hearing control ears. The hypothesis was that the presence of a cochlear implant can lead to an air-bone gap, causing absent air conduction stimuli VEMP responses, but present bone conduction vibration VEMP responses (indicating normal vestibular function), with changes in WAI as compared with ears with normal hearing. Further hypotheses were that subsets of ears with cochlear implants would (a) have present VEMP responses to both stimuli, indicating normal vestibular function and either normal or near-normal WAI, or (b) have absent VEMP responses to both stimuli, regardless of WAI, due to true vestibular loss.

DESIGN

Twenty-seven ears with cochlear implants (age range 7 to 31) and 10 ears with normal hearing (age range 7 to 31) were included in the study. All ears completed otoscopy, audiometric testing, 226 Hz tympanometry, WAI measures (absorbance), air conduction stimuli cervical and ocular VEMP testing through insert earphones, and bone conduction vibration cervical and ocular VEMP testing with a mini-shaker. Comparisons of VEMP responses to air and bone conduction stimuli, as well as absorbance responses between ears with normal hearing and ears with cochlear implants, were completed.

RESULTS

All ears with normal hearing demonstrated 100% present VEMP response rates for both stimuli. Ears with cochlear implants had higher response rates to bone conduction vibration compared with air conduction stimuli for both cervical and ocular VEMPs; however, this was only significant for ocular VEMPs. Ears with cochlear implants demonstrated reduced low-frequency absorbance (500 to 1200 Hz) as compared with ears with normal hearing. To further analyze absorbance, ears with cochlear implants were placed into subgroups based on their cervical and ocular VEMP response patterns. These groups were (1) present air conduction stimuli response, present bone conduction vibration response, (2) absent air conduction stimuli response, present bone conduction vibration response, and (3) absent air conduction stimuli response, absent bone conduction vibration response. For both cervical and ocular VEMPs, the group with absent air conduction stimuli responses and present bone conduction vibration responses demonstrated the largest decrease in low-frequency absorbance as compared with the ears with normal hearing.

CONCLUSIONS

Bone conduction VEMP response rates were increased compared with air-conduction VEMP response rates in ears with cochlear implants. Ears with cochlear implants also demonstrate changes in low-frequency absorbance consistent with a stiffer system. This effect was largest for ears that had absent air conduction but present bone conduction VEMPs. These findings suggest that this group, in particular, has a mechanical change that could lead to an air-bone gap, thus, abolishing the air conduction VEMP response due to an alteration in mechanics and not a true vestibular loss. Clinical considerations include using bone conduction vibration VEMPs and WAI for preoperative and postoperative testing in patients undergoing cochlear implantation.

Do Impedance Changes Correlate With a Delayed Hearing Loss After Hybrid L24 Implantation?

OBJECTIVES

Preservation of residual hearing is one of the main goals in present cochlear implantation surgery. Especially for this purpose, smaller and softer electrode carriers were developed that are to be inserted through the round window membrane to minimize trauma. By using these electrodes and insertion technique, residual hearing can be preserved in a large number of patients. Unfortunately, some of these patients with initially preserved residual hearing after cochlear implantation lose it later on. The reason for this is unknown but it is speculated about a correlation with an increase in impedance, since increased impedance values are linked to intracochlear inflammation and tissue reaction. Our hypothesis for this study design was that an increase in impedance predicts changes in residual hearing under clinical conditions.

DESIGN

Data of all adult patients (N = 122) receiving a Hybrid-L24 cochlear implant at our center between 2005 and early 2015 were retrospectively evaluated. Impedance values in Common Ground mode as measured during clinical routine and referring audiological test data (audiometric thresholds under headphones) were collected. Changes between consecutive measurements were calculated for impedance values and hearing thresholds for each patient. Correlations between changes in impedances and acoustic hearing thresholds were calculated. Average values were compared as well as patients with largest impedance changes within the observation period were evaluated separately.

RESULTS

Group mean values of impedances were between 5 and 7 kΩ and stable over time with higher values on basal electrode contacts compared with apical contacts. Average hearing thresholds at the time of initial fitting were between 40 to 50 dB (250 Hz) and 90 dB (1 kHz) with a loss of about 10 dB compared with preoperative values. Correlation between impedance changes and threshold changes was found, but too inconsistently to imply a true relationship. When evaluating the 20 patients with the largest impedance changes during the observation period (all >1 kΩ from one appointment to the next one), some patients were found where hearing loss is timely connected and highly correlated with an unusual impedance change. But large impedance changes were also observed without affecting hearing thresholds and hearing loss was found without impedance change.

CONCLUSIONS

Changes in impedance as measured during clinical routine cannot be taken as an indicator for a late acoustic hearing loss.

Magnetically Steered Robotic Insertion of Cochlear-Implant Electrode Arrays: System Integration and First-In-Cadaver Results

Cochlear-implant electrode arrays (EAs) must be inserted accurately and precisely to avoid damaging the delicate anatomical structures of the inner ear. It has previously been shown on the benchtop that using magnetic fields to steer magnet-tipped EAs during insertion reduces insertion forces, which correlate with insertion errors and damage to internal cochlear structures. This paper presents several advancements toward the goal of deploying magnetic steering of cochlear-implant EAs in the operating room. In particular, we integrate image guidance with patient-specific insertion vectors, we incorporate a new nonmagnetic insertion tool, and we use an electromagnetic source, which provides programmable control over the generated field. The electromagnet is safer than prior permanent-magnet approaches in two ways: it eliminates motion of the field source relative to the patient's head and creates a field-free source in the power-off state. Using this system, we demonstrate system feasibility by magnetically steering EAs into a cadaver cochlea for the first time. We show that magnetic steering decreases average insertion forces, in comparison to manual insertions and to image-guided robotic insertions alone.

Intracochlear fibrosis and the foreign body response to cochlear implant biomaterials

OBJECTIVE

To report current knowledge on the topic of intracochlear fibrosis and the foreign body response following cochlear implantation (CI).

METHODS

A literature search was performed in PubMed to identify peer-reviewed articles. Search components included "cochlear implant," "Foreign body response (FBR)," and "fibrosis." Original studies and review articles relevant to the topic were included.

RESULTS

Ninety peer-reviewed articles describing the foreign body response or intracochlear fibrosis following CI were included.

CONCLUSIONS

Intracochlear fibrosis following CI represents a significant limiting factor for the success of CI users. Several strategies have been employed to mitigate the foreign body response within the cochlea including drug delivery systems and modifications in surgical technique and electrode design. A better understanding of the FBR has the potential to improve CI outcomes and the next generation of cochlear prostheses.

Human Otopathologic Findings in Cases of Folded Cochlear Implant Electrodes

HYPOTHESIS

We hypothesize that human cases of cochlear implantation (CI) with folding of the electrode array will demonstrate greater degrees of intracochlear ossification, lower spiral ganglion neuron (SGN) counts, and poorer audiometric outcomes.

BACKGROUND

CI electrode array folding, such folding of the proximal array, is a relatively common surgical complication that can occur with forceful electrode insertion and may be an important and avoidable factor affecting implant outcomes. However, otopathologic findings and audiologic outcomes of human cases where folding of the implant electrode array is observed remain undefined.

METHODS

Specimens from a human temporal bone repository having undergone CI during life were evaluated. Specimens with folding of the electrode array on histological analysis constituted study cases. Electrode-matched specimens without array folding constituted controls. All specimens were examined by light microscopy and histopathologically described. Intracochlear fibrosis and osseous tissue, and SGN counts were measured. Pre- and postoperative word recognition scores were also compared.

RESULTS

Cases with folded electrodes showed greater volumes of intracochlear osseous tissue than controls, which was most prominent in areas adjacent to array folding. Both cases and controls demonstrated similar amounts of fibrous tissue. Folded cases showed decreased SGNs when compared with the contralateral ear, whereas controls showed stable SGN populations between ears. In this small cohort, postoperative hearing outcomes were similar between groups.

CONCLUSION

Atypical fibro-osseous changes and lower SGN counts are observed in cases of CI electrode folding. Future studies are necessary to determine if recognition and correction of folding can prevent long-term intracochlear changes.

Preservation of Cells of the Organ of Corti and Innervating Dendritic Processes Following Cochlear Implantation in the Human: An Immunohistochemical Study

HYPOTHESIS

This study evaluates the degree of preservation of hair cells, supporting cells, and innervating dendritic processes after cochlear implantation in the human using immunohistochemical methods.

BACKGROUND

Surgical insertion of a cochlear implant electrode induces various pathologic changes within the cochlea including insertional trauma, foreign body response, inflammation, fibrosis, and neo-osteogenesis. These changes may result in loss of residual acoustic hearing, adversely affecting the use of hybrid implants, and may result in loss of putative precursor cells, limiting the success of future regenerative protocols.

METHODS

Twenty-eight celloidin-embedded temporal bones from 14 patients with bilateral severe to profound sensorineural hearing loss and unilateral cochlear implants were studied. Two sections including the modiolus or basal turn from each temporal bone were stained using antineurofilament, antimyosin-VIIa, and antitubulin antibodies in both the implanted and unimplanted ears.

RESULTS

Inner and outer hair cells: Immunoreactivity was reduced throughout the implanted cochlea and in the unimplanted cochlea with the exception of the apical turn.Dendritic processes in the osseous spiral lamina: Immunoreactivity was significantly less along the electrode of the implanted cochlea than in the other segments.Inner and outer pillars, inner and outer spiral bundles, and Deiters' cells: Immunoreactivity was similar in the implanted and unimplanted cochleae.

CONCLUSION

Insertion of a cochlear implant electrode may significantly affect the inner and outer hair cells both along and apical to the electrode, and dendritic processes in the osseous spiral lamina along the electrode. There was less effect on pillar cells, Deiters' cells, and spiral bundles.

Design and Testing of a Bending-Resistant Transparent Nanocoating for Optoacoustic Cochlear Implants

A nanosized coating was designed to reduce fouling on the surface of a new type of cochlear implant relying on optoacoustic stimulation. This kind of device imposes novel design principles for antifouling coatings, such as optical transparency and resistance to significant constant bending. To reach this goal we deposited on poly(dimethylsiloxane) a PEO-based layer with negligible thickness compared to the curvature radius of the cochlea. Its antifouling performance was monitored upon storage by quartz crystal microbalance, and its resistance upon bending was tested by fluorescence microscopy under geometrical constraints similar to those of implantation. The coating displayed excellent antifouling features and good stability, and proved suitable for further testing in real-environment conditions.

Defining the Inflammatory Microenvironment in the Human Cochlea by Perilymph Analysis: Toward Liquid Biopsy of the Cochlea

The molecular pathomechanisms in the majority of patients suffering from acute or progressive sensorineural hearing loss cannot be determined yet. The size and the complex architecture of the cochlea make biopsy and in-depth histological analyses impossible without severe damage of the organ. Thus, histopathology correlated to inner disease is only possible after death. The establishment of a technique for perilymph sampling during cochlear implantation may enable a liquid biopsy and characterization of the cochlear microenvironment. Inflammatory processes may not only participate in disease onset and progression in the inner ear, but may also control performance of the implant. However, little is known about cytokines and chemokines in the human inner ear as predictive markers for cochlear implant performance. First attempts to use multiplex protein arrays for inflammatory markers were successful for the identification of cytokines, chemokines, and endothelial markers present in the human perilymph. Moreover, unsupervised cluster and principal component analyses were used to group patients by lead cytokines and to correlate certain proteins to clinical data. Endothelial and epithelial factors were detected at higher concentrations than typical pro-inflammatory cytokines such as TNF-a or IL-6. Significant differences in VEGF family members have been observed comparing patients with deafness to patients with residual hearing with significantly reduced VEGF-D levels in patients with deafness. In addition, there is a trend toward higher IGFBP-1 levels in these patients. Hence, endothelial and epithelial factors in combination with cytokines may present robust biomarker candidates and will be investigated in future studies in more detail. Thus, multiplex protein arrays are feasible in very small perilymph samples allowing a qualitative and quantitative analysis of inflammatory markers. More results are required to advance this method for elucidating the development and course of specific inner ear diseases or for perioperative characterization of cochlear implant patients.

Human Otopathology of Cochlear Implant Drill-out Procedures

OBJECTIVE

Human otopathology following drill-out procedures for cochlear implantation (CI) in cases with labyrinthitis ossificans (LO) has not been previously described. This study uses the high sensitivity of histopathology to (1) evaluate surgical drill-out technique with associated intracochlear findings and (2) quantify spiral ganglion neuron populations in a series of patients with LO who underwent CI.

STUDY DESIGN

Retrospective otopathology study.

SETTING

Otopathology laboratory.

SUBJECTS AND METHODS

Temporal bone (TB) specimens from cases with evidence of preoperative intracochlear fibroossification that required a drill-out procedure for CI electrode array insertion were included. All cases were histopathologically evaluated and 3-dimensional reconstructions of the cochleae were performed to interpret drilling paths and electrode trajectories.

RESULTS

Five TB specimens were identified, of which 4 underwent drill-out of the basal turn of the cochlea and 1 underwent a radical cochlear drill-out. In multiple TBs, drilling was imprecise with resultant damage to essential structures. Two TBs showed injury to the modiolus, which was associated with substantially decreased or even absent neuronal populations within these areas. In addition, 2 cases with inadequate drill-out or extensive LO of the basal turn resulted in extracochlear placement of electrode arrays into the vestibule due to persistent obstruction within the basal turn.

CONCLUSION

Otopathology highlights the challenges of drill-out procedures in cases of LO. Imprecise drilling paths, due to distortion of normal cochlear anatomy, risk injury to the modiolus and adjacent neurons as well as extracochlear placement of electrode arrays, both of which may contribute to poorer hearing outcomes.

Intracochlear tPA infusion may reduce fibrosis caused by cochlear implantation surgery

BACKGROUND

Experiments show that the extent of ongoing fibrotic change within the cochlea can be determined by the volume and pattern of bleeding within the first 24 h following cochlear implantation. Tissue-type plasminogen activator (tPA) is effective at reducing thrombus volume when administered both within and external to the systemic circulation.

AIMS/OBJECTIVES

To determine if tPA delivered into the scala tympani immediately following implantation will reduce thrombus volume within the lower basal turn of the cochlea.

MATERIALS AND METHODS

Guinea pigs were implanted with either 'soft' or 'hard' arrays and administered tPA or saline via an intra-cochlear infusion immediately after implantation. Hearing was checked prior to, and 2 weeks after implantation. Cochleae were then harvested and imaged.

RESULTS

Animals implanted with 'soft' arrays had 4.2% less tissue response compared with animals implanted with 'hard' arrays. In animals receiving 'soft' arrays, tPA reduced the volume of tissue response (measured by the percentage of the lower basal turn of the scala tympani occupied by tissue response) compared with saline.

CONCLUSIONS AND SIGNIFICANCE

tPA may be effective in reducing the overall volume of tissue response in routine 'soft' cochlear implantation and may have a greater effect in the event of significant surgical trauma.

Lower initial electrode impedances in minimally invasive cochlear implantation

BACKGROUND

The round window approach and the cochleostomy approach are two widely practiced methods to insert cochlear implant electrode arrays. Yet, there is no consensus on which is more minimally invasive.

OBJECTIVE

To compare the initial electrode impedance (EI) values and the incidence of abnormal electrodes of the round window approach and the cochleostomy approach, and to evaluate the effects of surgical techniques on the intracochlear microenvironment.

MATERIAL AND METHODS

One hundred and seventy-one patients received a unilateral Nucleus cochlear implant. Eighty-two patients were implanted using the round window approach, and 89 patients were implanted using the cochleostomy approach. EI was measured immediately after closure of the incision.

RESULTS

The round window group had lower average initial EI values than the cochleostomy group. For the EI values at each position, statistically significant differences were found in the basal-middle region (Electrode 1-14), but not in the middle-apical region (Electrode 15-22) of the electrode arrays. A lower incidence of high-impedance electrodes was found in the round window group.

CONCLUSIONS

The round window approach leads to lower initial EI and less disturbance to the intracochlear microenvironment.

Exploiting Routine Clinical Measures to Inform Strategies for Better Hearing Performance in Cochlear Implant Users

Neuroprostheses designed to interface with the nervous system to replace injured or missing senses can significantly improve a patient's quality of life. The challenge remains to provide implants that operate optimally over several decades. Changes in the implant-tissue interface may precede performance problems. Tools to identify and characterize such changes using existing clinical measures would be highly valuable. Modern cochlear implant (CI) systems allow easy and regular measurements of electrode impedance (EI). This measure is routinely performed as a hardware integrity test, but it also allows a level of insight into the immune-mediated response to the implant, which is associated with performance outcomes. This study is a 5-year retrospective investigation of MED-EL CI users at the University of Southampton Auditory Implant Service including 176 adult ears (18-91) and 74 pediatric ears (1-17). The trend in EI in adults showed a decrease at apical electrodes. An increase was seen at the basal electrodes which are closest to the surgery site. The trend in the pediatric cohort was increasing EI over time for nearly all electrode positions, although this group showed greater variability and had a smaller sample size. We applied an outlier-labeling rule to statistically identify individuals that exhibit raised impedance. This highlighted 14 adult ears (8%) and 3 pediatric ears (5%) with impedance levels that deviated from the group distribution. The slow development of EI suggests intra-cochlear fibrosis and/or osteogenesis as the underlying mechanism. The usual clinical intervention for extreme impedance readings is to deactivate the relevant electrode. Our findings highlight some interesting clinical contradictions: some cases with raised (but not extreme) impedance had not prompted an electrode deactivation; and many cases of electrode deactivation had been informed by subjective patient reports. This emphasizes the need for improved objective evidence to inform electrode deactivations in borderline cases, for which our outlier-labeling approach is a promising candidate. A data extraction and analysis protocol that allows ongoing and automated statistical analysis of routinely collected data could benefit both the CI and wider neuroprosthetics communities. Our approach provides new tools to inform practice and to improve the function and longevity of neuroprosthetic devices.

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

BACKGROUND

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

AIM

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

PATIENTS AND METHODS

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

RESULTS

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

CONCLUSIONS AND SIGNIFICANCE

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

Intracochlear administration of steroids with a catheter during human cochlear implantation: a safety and feasibility study

Suppression of foreign body reaction, improvement of electrode-nerve interaction, and preservation of residual hearing are essential research topics in cochlear implantation. Intracochlear pharmaco- or cell-based therapies can open new horizons in this field. Local drug delivery strategies are desirable as higher local concentrations of agents can be realized and side effects can be minimized compared to systemic administrations. When administered locally at accessible, basal parts of the cochlea, drugs reach apical regions later and in much lower concentrations due to poor diffusion patterns in cochlear fluids. Therefore, new devices are needed to warrant rapid distribution of agents into all parts of the cochlea. Five patients received a deep intracochlear injection of triamcinolone with a specifically designed cochlear catheter during cochlear implantation right before inserting a cochlear implant electrode. As a measure for formation of fibrous tissue around the electrode, electrical impedances were measured in the operation room and over 4 months thereafter. No adverse events were observed peri- and postoperatively. The handling of the device was easy. Severe damage to the microstructure of the cochlea was excluded as far as possible by cone beam computed tomography and vestibular testing. A delayed rise of the impedances was seen in the catheter group compared to controls over all regions of the cochlea. A statistical significance, however, was only obtained at the midregion of the cochlea. Consequently, the cochlear catheter is a safe and feasible device for local drug delivery of pharmaceutical agents into deeper regions of the cochlea.

ECAP growth function to increasing pulse amplitude or pulse duration demonstrates large inter-animal variability that is reflected in auditory cortex of the guinea pig

Despite remarkable advances made to ameliorate how cochlear implants process the acoustic environment, many improvements can still be made. One of most fundamental questions concerns a strategy to simulate an increase in sound intensity. Psychoacoustic studies indicated that acting on either the current, or the duration of the stimulating pulses leads to perception of changes in how loud the sound is. The present study compared the growth function of electrically evoked Compound Action Potentials (eCAP) of the 8^th nerve using these two strategies to increase electrical charges (and potentially to increase the sound intensity). Both with chronically (experiment 1) or acutely (experiment 2) implanted guinea pigs, only a few differences were observed between the mean eCAP amplitude growth functions obtained with the two strategies. However, both in chronic and acute experiments, many animals showed larger increases of eCAP amplitude with current increase, whereas some animals showed larger of eCAP amplitude with duration increase, and other animals show no difference between either approaches. This indicates that the parameters allowing the largest increase in eCAP amplitude considerably differ between subjects. In addition, there was a significant correlation between the strength of neuronal firing rate in auditory cortex and the effect of these two strategies on the eCAP amplitude. This suggests that pre-selecting only one strategy for recruiting auditory nerve fibers in a given subject might not be appropriate for all human subjects.

Platinum corrosion products from electrode contacts of human cochlear implants induce cell death in cell culture models

Despite the technological progress made with cochlear implants (CI), impedances and their diagnosis remain a focus of interest. Increases in impedance have been related to technical defects of the electrode as well as inflammatory and/or fibrosis along the electrode. Recent studies have demonstrated highly increased impedances as the result of corroded platinum (Pt) electrode contacts. This in vitro study examined the effects of Pt ions and compounds generated by corrosion of the electrode contacts of a human CI on cell metabolism. Since traces of solid Pt in surrounding cochlear tissues have been reported, the impact of commercially available Pt nanoparticles (Pt-NP, size 3 nm) on the cell culture model was also determined. For this purpose, the electrode contacts were electrically stimulated in a 0.5% aqueous NaCl solution for four weeks and the mass fraction of the platinum dissolute (Pt-Diss) was determined by mass spectrometry (ICP-MS). Metabolic activity of the murine fibroblasts (NIH 3T3) and the human neuroblastoma (SH-SY5Y) cells was determined using the WST-1 assay following exposure to Pt-Diss and Pt-NP. It was found that 5–50 μg/ml of the Pt-NP did not affect the viability of both cell types. In contrast, 100 μg/ml of the nanoparticles caused significant loss in metabolic activity. Furthermore, transmission electron microscopy (TEM) revealed mitochondrial swelling in both cell types indicating cytotoxicity. Additionally, TEM demonstrated internalized Pt-NP in NIH 3T3 cells in a concentration dependent manner, whereas endocytosis in SH-SY5Y cells was virtually absent. In comparison with the Pt-NP, the corrosion products (Pt-Diss) with concentrations between 1.64 μg/ml and 8.2 μg/ml induced cell death in both cell lines in a concentration dependent manner. TEM imaging revealed both mitochondrial disintegration and swelling of the endoplasmic reticulum, suggesting that Pt ions trigger cytotoxicity in both NIH 3T3 and SH-SY5Y cell lines by interacting with the respiratory chain.

Variations in electrode impedance during and after cochlear implantation: Round window versus extended round window insertions

OBJECTIVES

To assess differences in intra- and postoperative electrode impedances following cochlear implantation between round window insertions (RWI) and extended round window insertions (ERWI).

METHODS

Fifty patients with congenital hearing loss received unilateral hearing implants (Sonata Ti100, Med-El GmbH, Innsbruck, Austria) with standard electrode arrays. The patients were divided into two groups according to the surgical technique used. Thirty-five procedures were performed with RWI (group A) and 15 with ERWI (group B). Electrode impedance was measured and analysed during the operation, and one week and one month postoperatively.

RESULTS

There were no statistically significant differences (i.e., P > 0.05) in electrode impedance between groups A and B intraoperatively, or at one week or one month postoperatively. Electrode impedance at one month postoperatively was higher than the intraoperative and postoperative one week values in group A (P < 0.05), with similar results in group B.

CONCLUSION

There was no significant difference between RWI and ERWI in operative duration or complications of cochlear implantation. Moreover, no significant differences in postoperative electrode impedance values were found between the two surgical routes.

Surgical treatment of vertigo in cochlear implantees by electrode resealing

CONCLUSION

Our present findings demonstrate that resealing to cover the electrode is an effective method to treat vertigo after CI. An insufficient cochleostomy sealing can be regarded as a cause of postoperatively newly occuring vertigo after CI. A transtympanic revision is a promising treatment option in cases of post-operative dizziness. Intoduction: A well-known and frequently reported complication after cochlear implantation is the appearance of postoperative vertigo symptoms. The aim of the present study was to observe if the postoperatively new occurrence of vertigo can be treated by resealing of the round window patch after cochlear implantation.

MATERIAL AND METHODS

A retrospective analysis revealed that 10 patients underwent revision surgery transtympanally. Vertigo was assessed preoperatively and directly postoperatively and after 6 month after revision surgery by using the Dizziness Handycap Inventory (DHI).

RESULTS

The most common symptom was rotating vertigo. A spontanous nystagmus was seen in four cases. No nystagmus was found after the revision surgery. In three cases, the onset of dizziness was associated with an event (sneezing, otitis media, climbing a mountain). A preoperative CT showed insuspectible results in seven patients but revealed pathologies two patients. Vertigo was improved significantly in six patients, and three of them were symptom-free.

A Preliminary Investigation of the Air-Bone Gap: Changes in Intracochlear Sound Pressure With Air- and Bone-conducted Stimuli After Cochlear Implantation

HYPOTHESIS

A cochlear implant electrode within the cochlea contributes to the air-bone gap (ABG) component of postoperative changes in residual hearing after electrode insertion.

BACKGROUND

Preservation of residual hearing after cochlear implantation has gained importance as simultaneous electric-acoustic stimulation allows for improved speech outcomes. Postoperative loss of residual hearing has previously been attributed to sensorineural changes; however, presence of increased postoperative ABG remains unexplained and could result in part from altered cochlear mechanics. Here, we sought to investigate changes to these mechanics via intracochlear pressure measurements before and after electrode implantation to quantify the contribution to postoperative ABG.

METHODS

Human cadaveric heads were implanted with titanium fixtures for bone conduction transducers. Velocities of stapes capitulum and cochlear promontory between the two windows were measured using single-axis laser Doppler vibrometry and fiber-optic sensors measured intracochlear pressures in scala vestibuli and tympani for air- and bone-conducted stimuli before and after cochlear implant electrode insertion through the round window.

RESULTS

Intracochlear pressures revealed only slightly reduced responses to air-conducted stimuli consistent with previous literature. No significant changes were noted to bone-conducted stimuli after implantation. Velocities of the stapes capitulum and the cochlear promontory to both stimuli were stable after electrode placement.

CONCLUSION

Presence of a cochlear implant electrode causes alterations in intracochlear sound pressure levels to air, but not bone, conducted stimuli and helps to explain changes in residual hearing noted clinically. These results suggest the possibility of a cochlear conductive component to postoperative changes in hearing sensitivity.

Histopathology of the Human Inner Ear in the Cogan Syndrome with Cochlear Implantation

The Cogan syndrome is a rare disorder characterized by nonsyphilitic interstitial keratitis and audiovestibular symptoms. Profound sensorineural hearing loss has been reported in approximately half of the patients with the Cogan syndrome resulting in candidacy for cochlear implantation in some patients. The current study is the first histopathologic report on the temporal bones of a patient with the Cogan syndrome who during life underwent bilateral cochlear implantation. Preoperative MRI revealed tissue with high density in the basal turns of both cochleae and both vestibular systems consistent with fibrous tissue due to labyrinthitis. Histopathology demonstrated fibrous tissue and new bone formation within the cochlea and vestibular apparatus, worse on the right. Severe degeneration of the vestibular end organs and new bone formation in the labyrinth were seen more on the right than on the left. Although severe bilateral degeneration of the spiral ganglion neurons was seen, especially on the right, the postoperative word discrimination score was between 50 and 60% bilaterally. Impedance measures were generally higher in the right ear, possibly related to more fibrous tissue and new bone found in the scala tympani on the right side.

Cochlear Histopathology as Observed in Two Patients With a Cochlear Implant Electrode With Positioner

HYPOTHESIS

This study reports the cochlear histopathology of two patients who during life underwent cochlear implantation with a positioner.

BACKGROUND

A silastic positioner introduced by the Advanced Bionics Corporation in 1999 was designed to position the electrode of the cochlear implant close to the modiolus. The positioner was recalled in the United States in July 2002 because of an apparent higher incidence of bacterial meningitis in patients in whom the positioner had been placed.

METHODS

Four celloidin-embedded temporal bones from two patients with cochlear implants with a positioner from the temporal bone collection of the Massachusetts Eye and Ear Infirmary were included in the study. In a previous study, we reported histopathologic findings in Patient 1, and in this report, we present the findings in a second case in a 94-year-old woman (Patient 2), and the similarities and differences between the two patients. All four specimens were prepared for histologic study by conventional techniques and 2-D reconstruction.

RESULTS

Evidence of insertion trauma was observed in all three implanted specimens. More significant trauma was found in Patient 2 than in Patient 1 including disruption of the osseous spiral lamina and the basilar membrane. In addition, there was more new fibrous tissue and bone in Patient 2 than in Patient 1. There was a large fluid space in all three implanted temporal bones around the electrode and positioner.

CONCLUSION

The findings observed in the two patients may help to explain the increased risk of meningitis in patients implanted with a positioner.

Advances in translational inner ear stem cell research

Stem cell research is expanding our understanding of developmental biology as well as promising the development of new therapies for a range of different diseases. Within hearing research, the use of stem cells has focused mainly on cell replacement. Stem cells however have a broad range of other potential applications that are just beginning to be explored in the ear. Mesenchymal stem cells are an adult derived stem cell population that have been shown to produce growth factors, modulate the immune system and can differentiate into a wide variety of tissue types. Potential advantages of mesenchymal/adult stem cells are that they have no ethical constraints on their use. However, appropriate regulatory oversight seems necessary in order to protect patients from side effects. Disadvantages may be the lack of efficacy in many preclinical studies. But if proven safe and efficacious, they are easily translatable to clinical trials. The current review will focus on the potential application on mesenchymal stem cells for the treatment of inner ear disorders.

Cochlear implant electrode sealing techniques and related intracochlear pressure changes

Background

The inserted cochlear implanted electrode is covered at the site of the round window or cochleostomy to prevent infections and leakage. In a surgically hearing preservational concept, low intracochlear pressure changes are of high importance. The aim of this study was to observe intracochlear pressure changes due to different sealing techniques in a cochlear model.

Methods

Cochlear implant electrode insertions were performed in an artifical cochlear model and the intracochlear pressure changes were recorded in parallel with a micro-pressure sensor positioned in the apical region of the cochlea model to follow the maximum amplitude of intracochlear pressure. Four different sealing conditions were compared: 1) overlay, 2) overlay with fascia pushed in, 3) donut-like fascia ring, 4) donut-like fascia ring pushed in.

Results

We found statistically significant differences in the occurrence of maximum amplitude of intracochlear pressure peak changes related to sealing procedure comparing the different techniques. While the lowest amplitude changes could be observed for the overlay technique (0.14 mmHg ± 0.06) the highest values could be observed for the donut-like pushed in technique (1.79 mmHg ± 0.69).

Conclusion

Sealing the electrode inserted cochlea can lead to significant intracochlear pressure changes. Pushing in of the sealing tissue cannot be recommended.

Evolution of impedance field telemetry after one day of activation in cochlear implant recipients

OBJECTIVES

Changes in impedance between 24 hours and one month after cochlear implantation have never been explored due to the inability to switch on within one day. This study examined the effect of early activation (within 24 hours) on the evolution of electrode impedance with the aim of providing information on the tissue-to-electrode interface when electrical stimulation was commenced one day post implantation.

METHODS

We performed a retrospective review at a single institution. Patients who received a Nucleus 24RECA implant system (Cochlear, Sydney, Australia) and underwent initial switch-on within 24 hours postoperatively were included. Impedance measurements were obtained intraoperatively and postoperatively at 1 day, 1 week, 4 weeks, and 8 weeks.

RESULTS

A significant drop in impedance was noted 1 day after an initial activation within 24 hours followed by a significant rise in impedance in all channels until 1 week, after which the impedance behaved differently in different segments. Basal and mid-portion electrodes revealed a slight increase while apical electrodes showed a slight decrease in impedance from 1 week to 8 weeks postoperatively. Impedance was relatively stable 4 weeks after surgery.

CONCLUSIONS

This is the first study to report the evolution of impedance in all channels between initial mapping 1 day and 1 month after cochlear implantation. The underlying mechanism for the differences in behavior between different segments of the electrode may be associated with the combined effect of dynamics among the interplay of cell cover formation, electrical stimulation, and fibrotic reaction.

The pattern and degree of capsular fibrous sheaths surrounding cochlear electrode arrays

An inflammatory tissue reaction around the electrode array of a cochlear implant (CI) is common, in particular at the electrode insertion region (cochleostomy) where mechanical trauma often occurs. However, the factors determining the amount and causes of fibrous reaction surrounding the stimulating electrode, especially medially near the perimodiolar location, are unclear. Temporal bone (TB) specimens from patients who had undergone cochlear implantation during life with either Advanced Bionics (AB) Clarion ™ or HiRes90K™ (Sylmar, CA, USA) devices that have a half-band and a pre-curved electrode, or Cochlear ™ Nucleus (Sydney, Australia) device that have a full-band and a straight electrode were evaluated. The thickness of the fibrous tissue surrounding the electrode array of both types of CI devices at both the lower (LB) and upper (UB) basal turns of the cochlea was quantified at three locations: the medial, inferior, and superior aspects of the sheath. Fracture of the osseous spiral lamina and/or marked displacement of the basilar membrane were interpreted as evidence of intracochlear trauma. In addition, post-operative word recognition scores, duration of implantation, and post-operative programming data were evaluated. Seven TBs from six patients implanted with AB devices and five TBs from five patients implanted with Nucleus devices were included. A fibrous capsule around the stimulating electrode array was present in all twelve specimens. TBs implanted with AB device had a significantly thicker fibrous capsule at the medial aspect than at the inferior or superior aspects at both locations (LB and UB) of the cochlea (Wilcoxon signed-ranks test, p < 0.01). TBs implanted with a Nucleus device had no difference in the thickness of the fibrous capsule surrounding the track of the electrode array (Wilcoxon signed-ranks test, p > 0.05). Nine of fourteen (64%) basal turns of the cochlea (LB and UB of seven TBs) implanted with AB devices demonstrated intracochlear trauma compared to two of ten (20%) basal turns of the cochlea (LB and UB of five TBs) with Nucleus devices, (Fisher exact test, p < 0.05). There was no significant correlation between the thickness of the fibrous tissue and the duration of implantation or the word recognition scores (Spearman rho, p = 0.06, p = 0.4 respectively). Our outcomes demonstrated the development of a robust fibrous tissue sheath medially closest to the site of electric stimulation in cases implanted with the AB device electrode, but not in cases implanted with the Nucleus device. The cause of the asymmetric fibrous sheath may be multifactorial including insertional trauma, a foreign body response, and/or asymmetric current flow.

A silicone fiber coating as approach for the reduction of fibroblast growth on implant electrodes

In cochlear implant (CI) patients, an increase in electrode impedance due to fibrotic encapsulation is frequently observed. Several attempts have been proposed to reduce fibroblast growth at the electrode contacts, but none proved to be satisfactory so far. Here, a silicone fiber coating of the electrode contacts is presented that provides a complex micro-scale surface topography and increases hydrophobicity to inhibit fibroblast growth and adhesion. A silicone fiber electrospinning process was developed to create a thin and porous fiber mesh. Fiber coatings were applied on graphite specimen holders, glass cover slips and CI electrode contacts. For characterization of the coating's pore distribution, water contact angle and electrical impedance were analyzed. Cytotoxicity and in vitro fibroblast growth were evaluated to assess biological efficacy of the coatings. It could be shown that the silicone fiber mesh itself had only minor influence on electrode impedance. A uniform, hydrophobic fiber coating could be achieved that decreased fibroblast growth without showing toxic effects. Finally, CI electrode contacts were successfully coated in order to present this promising approach for a long-term improvement of CI electrodes. We are one of the first groups that could successfully adapt the electrospinning technique on the utilization of silicone. Silicone was chosen because of its high hydrophobicity, chemical stability and excellent biocompatibility and as it is one of the biomaterials already used in CIs. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2574-2580, 2017.