Cochlear implant electrode insertion: in defence of cochleostomy and factors against the round window membrane approach

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.

An In-Vitro Insertion-Force Study of Magnetically Guided Lateral-Wall Cochlear-Implant Electrode Arrays

Hypothesis:

Insertion forces can be reduced by magnetically guiding the tip of lateral-wall cochlear-implant electrode arrays during insertion via both cochleostomy and the round window.

Background:

Steerable electrode arrays have the potential to minimize intracochlear trauma by reducing the severity of contact between the electrode-array tip and the cochlear wall. However, steerable electrode arrays typically have increased stiffness associated with the steering mechanism. In addition, steerable electrode arrays are typically designed to curve in the direction of the basal turn, which is not ideal for round-window insertions, as the cochlear hook's curvature is in the opposite direction. Lateral-wall electrode arrays can be modified to include magnets at their tips, augmenting their superior flexibility with a steering mechanism. By applying magnetic torque to the tip, an electrode array can be navigated through the cochlear hook and the basal turn.

Methods:

Automated insertions of candidate electrode arrays are conducted into a scala-tympani phantom with either a cochleostomy or round-window opening. The phantom is mounted on a multi-degree-of-freedom force sensor. An external magnet applies the necessary magnetic bending torque to the magnetic tip of a modified clinical electrode array, coordinated with the insertion, with the goal of directing the tip down the lumen. Steering of the electrode array is verified through a camera.

Results:

Statistical t-test results indicate that magnetic guidance does reduce insertion forces by as much as 50% with certain electrode-array models. Direct tip contact with the medial wall through the cochlear hook and the lateral wall of the basal turn is completely eliminated. The magnetic field required to accomplish these insertions varied from 77 to 225 mT based on the volume of the magnet at the tip of the electrode array. Alteration of the tip to accommodate a tiny magnet is minimal and does not change the insertion characteristic of the electrode array unless the tip shape is altered.

Conclusion:

Magnetic guidance can eliminate direct tip contact with the medial walls through the cochlear hook and the lateral walls of the basal turn. Insertion-force reduction will vary based on the electrode-array model, but is statistically significant for all models tested. Successful steering of lateral-wall electrode arrays is accomplished while maintaining its superior flexibility.

Effects of Various Trajectories on Tissue Preservation in Cochlear Implant Surgery: A Micro-Computed Tomography and Synchrotron Radiation Phase-Contrast Imaging Study

OBJECTIVES

The purpose of this study was to evaluate the three-dimensional (3D) anatomy and potential damage to the hook region of the human cochlea following various trajectories at cochlear implantation (CI). The goal was to determine which of the approaches can avoid lesions to the soft tissues, including the basilar membrane and its suspension to the lateral wall. Currently, there is increased emphasis on conservation of inner ear structures, even in nonhearing preservation CI surgery.

DESIGN

Micro-computed tomography and various CI approaches were made in an archival collection of macerated and freshly fixed human temporal bones. Furthermore, synchrotron radiation phase-contrast imaging was used to reproduce the soft tissues. The 3D anatomy was investigated using bony and soft tissue algorithms, and influences on inner ear structures were examined.

RESULTS

Micro-computed tomography with 3D rendering demonstrated the topography of the round window (RW) and osseous spiral laminae, while synchrotron imaging allowed reproduction of soft tissues such as the basilar membrane and its suspension around the RW membrane. Anterior cochleostomies and anteroinferior cochleostomies invariably damaged the intracochlear soft tissues while inferior cochleostomies sporadically left inner ear structures unaffected.

CONCLUSIONS

Results suggest that cochleostomy approaches often traumatize the soft tissues at the hook region at CI surgery. For optimal structural preservation, the RW approach is, therefore, recommended.

Anatomical Study of the Facial Recess with Implications in Round Window Visibility for Cochlear Implantation: Personal Observations and Review of the Literature

Introduction  Posterior tympanotomy through facial recess (FR) is the conventional and most preferred approach to facilitate cochlear implantation, especially when the electrode is inserted through the round window. The complications of the FR approach can be minimized by proper understanding of the anatomy of the FR.

Objective  The present study was undertaken to assess the various parameters of FR and round window visibility, which may be of relevance for cochlear implant surgery.

Methods  Thirty-five normal wet human cadaveric temporal bones were studied by dissection for anatomy of FR and posterior tympanum. Photographs were taken with an 18 megapixels digital camera, which were then imported to a computer to determine various parameters.

Results  The mean distance from the take-off point/crotch of the chorda tympani nerve (CTN) to the stylomastoid foramen was 4.08 ± 0.8 mm (range of 2.06 - 5.5 mm). The variations in the course of the CTN included origin at the level of the lateral semicircular canal. The mean chorda-facial angle in our study was 26.91° ± 1.19°, with a range of 25° to 28.69°. The mean FR length ranged between 9.4 mm and 18.56 mm (mean of 12.41 ± 2.91mm) and varied with the origin of the CTN and pneumatization of temporal bone. The average maximum width of the FR was 2.93 ± 0.4 mm (range 2.24–3.45 mm) and the mean width of the FR at the level of the round window was 2.65 ± 0.41 mm.

Conclusion  The FR approach provides good access to the round window membrane in all cases. In some cases, table adjustment is required.

Comparison of electrode position between round window and cochleostomy inserting approaches among young children: a cone-beam computed tomography study

BACKGROUND

As the two most commonly used approaches for cochlear implants (CIs), the round-window insertion (RWI) and cochleostomy are still controversial about which approach is optimal. The lack of visual observation methods makes it difficult to compare the electrode position between them.

OBJECTIVES

To evaluate and compare the electrode position between RWI and cochleostomy approaches for CI among young children.

MATERIALS AND METHODS

Twenty-four patients (16 male, 8 female) accepting CI and temporal cone-beam computed tomography (CBCT) scan post-operation in our hospital from January 2016 to July 2017 were analyzed retrospectively. Operative notes and images were used to identify the surgical technique. Mainly depending on the round-window exposure, 15 cochleae were performed with RWI and 11 performed with cochleostomy.

RESULTS

Mean age, 2.4 (range 0.8-7) years. The CBCT images showed that all the electrode arrays were located in scala tympani. There were no significantly statistical differences in the distance between electrode contacts and modiolus (EMI), intracochlear insertion length and the angle of electrode arrays at the insertion site of the cochlea.

CONCLUSIONS AND SIGNIFICANCE

Both approaches could insert electrodes into scala tympani satisfactorily. As electrodes and cochlear structures could be clearly visualized, CBCT can be applied to assess the electrode position reliably.

Mimic Cochlear Implant Surgery-Induced Cochlear Infection Fails to Further Damage Auditory Pathway in Deafened Guinea Pigs

Background

Kanamycin and subsequent furosemide administration was applied to the healthy guinea pigs to induce deafness.

Material/Methods

Of the deafened guinea pigs, 10 were further infused with anti-infection procedures (Group B) and the other 10 animals did not undergo anti-infection procedures (Group C). In Group B, the deafened animals were able to restore cochlear and middle ear functions following the anti-infection procedure. In Group C, all animals developed cochlear and middle ear infections.

Results

Compared to the healthy guinea pigs, hair cells and spiral ganglion neurons (SGN) of deafened animals (in Group B and Group C) were severely damaged. SGN density of deafened animals was significantly lower than that of healthy control animals in all ear turns except the basal turn. There was no significant difference between Group B and Group C in SGN density. The average optical density value of neurofilaments of deafened animals was also significantly decreased after the ototoxic drug administration. Notably, the density of the neurons in the cochlear nucleus region (CNR) of the brainstem were not significantly different between the healthy control guinea pigs and deafened animals.

Conclusions

Mimic cochlear implant surgery-induced cochlear infection caused no significant damage to the auditory pathway in ototoxic drug-induced deafened guinea pigs.

Meta-analysis of subjective complaints of vertigo and vestibular tests after cochlear implantation

OBJECTIVE

Postoperative vertigo is a common complaint after cochlear implantation, but published incidence rates differ vastly. The aim of the present study was to investigate both subjective complaints of vertigo before and after cochlear implantation and related vestibular diagnostic tests on cochlear implant candidates.

DATA SOURCES

We performed a systematic literature search according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement in PubMed, Cochrane Register, and EMBASE.

REVIEW METHODS

We presented 116 eligible studies investigating subjective complaints of vertigo after cochlear implantation and/or related vestibular diagnostic tests. We conducted three meta-analyses of 46 eligible studies with matched pre- and postoperative data to calculate the odds ratio of new vertigo onset, as well as the impairment of vestibular receptors measured by nystagmography and cervical vestibular evoked myogenic potentials (cVEMP). Postoperative vertigo was calculated from 95 studies and further subdivided by mean age with pooled data.

RESULTS

We observed a significant increase in postoperative vertigo and significant impairment of nystagmography and cVEMP detection. Vertigo after cochlear implantation was reported in 9.3% of the patients with a continuous increase in patient age at surgery. In a subgroup of studies, new onset of vertigo was found in 17.4% of the patients. In addition, 7.2% of the patients had persisting vertigo complaints, whereas 11.6% described an altered vertigo quality and 7.7% had their preoperative complaints resolved. A comparison of round window approach and cochleostomy revealed significantly increased vertigo after cochleostomy. Both insertion methods showed similar effects in nystagmography and cVEMP testing.

CONCLUSION

Cochlear implantation has a significant impact on subjective vertigo and vestibular receptor function. This is affected by the patient's age at the time of surgery. The surgical technique (round window or cochleostomy) may influence the outcome, but this requires further investigation. Younger patients may compensate better following vestibular dysfunction. Perioperative testing is required to correlate vestibular impairment and subjective complaints. Laryngoscope, 2018 Laryngoscope, 128:2110-2123, 2018.

Impact of the surgical experience on cochleostomy location: a comparative temporal bone study between endaural and posterior tympanotomy approaches for cochlear implantation

The goal of this study was to evaluate, in the hands of an inexperienced surgeon, the cochleostomy location of an endaural approach (MINV) compared to the conventional posterior tympanotomy (MPT) approach. Since 2010, we use in the ENT department of Nice a new surgical endaural approach to perform cochlear implantation. In the hands of an inexperienced surgeon, the position of the cochleostomy has not yet been studied in detail for this technique. This is a prospective study of 24 human heads. Straight electrode arrays were implanted by an inexperienced surgeon: on one side using MPT and on the other side using MINV. The cochleostomies were all antero-inferior, but they were performed through an endaural approach with the MINV or a posterior tympanotomy approach with the MPT. The positioning of the cochleostomies into the scala tympani was evaluated by microdissection. Cochleostomies performed through the endaural approach were well placed into the scala tympani more frequently than those performed through the posterior tympanotomy approach (87.5 and 16.7 %, respectively, p ≤ 0.001). This study highlights the biggest challenge for an inexperienced surgeon to achieve a reliable cochleostomy through a posterior tympanotomy, which requires years of experience. In case of an uncomfortable view through a posterior tympanotomy, an inexperienced surgeon might be able to successfully perform a cochleostomy through an endaural (combined approach) or an extended round window approach in order to avoid opening the scala vestibuli.

On the anatomy of the 'hook' region of the human cochlea and how it relates to cochlear implantation

BACKGROUND

The optimal insertion route for an electrode array in hearing preservation cochlear implantation (CI) surgery is still tentative. Both cochleostomy (CO) and round window (RW) techniques are used today. In the present study we analyzed size variations and topographic anatomy of the 'hook' region of the human cochlea to better comprehend the Testo effects of various electric array insertion modes.

MATERIAL AND METHODS

Size variations of the cochlear 'hook' region were assessed in 23 human, microdissected temporal bones by measuring the distances between the oval and round windows, also outlining the spiral ligament/spiral lamina. Influence of size variations on spiral ligament position and fundamentals for different surgical approaches were evaluated in a subset of 'small' and 'large' cochleae performing different types of CO. In addition, the relationship between the microdissected accessory canal housing the inferior cochlear vein and the RW was analyzed.

RESULTS

The lateral vestibular wall and the cochlear 'hook' displayed large anatomic variations that greatly influenced the size of the potential surgical area. RESULTS showed that only very inferiorly located CO entered the scala tympani without causing trauma to the spiral ligament and spiral lamina. An inferior approach may challenge the inferior cochlear vein.

CONCLUSION

Preoperative assessment of the distance between the round and oval windows may direct the surgeon before CI hearing-preservation surgery. CO techniques, especially in 'small' ears, may lead to frequent damage to the inner ear structures. In those cases with substantial residual hearing, CI surgery may be better performed through a RW approach.

The role of intracochlear drug delivery devices in the management of inner ear disease

INTRODUCTION

Diseases of the inner ear include those of the auditory and vestibular systems, and frequently result in disabling hearing loss or vertigo. Despite a rapidly expanding pipeline of potential cochlear therapeutics, the inner ear remains a challenging organ for targeted drug delivery, and new technologies are required to deliver these therapies in a safe and efficacious manner. In addition to traditional approaches for direct inner ear drug delivery, novel microfluidics-based systems are under development, promising improved control over pharmacokinetics over longer periods of delivery, ultimately with application towards hair cell regeneration in humans.

AREAS COVERED

Advances in the development of intracochlear drug delivery systems are reviewed, including passive systems, active microfluidic technologies and cochlear prosthesis-mediated delivery. This article provides a description of novel delivery systems and their potential future clinical applications in treating inner ear disease.

EXPERT OPINION

Recent progresses in microfluidics and miniaturization technologies are enabling the development of wearable and ultimately implantable drug delivery microsystems. Progress in this field is being spurred by the convergence of advances in molecular biology, microfluidic flow control systems and models for drug transport in the inner ear. These advances will herald a new generation of devices, with near-term applications in preclinical models, and ultimately with human clinical use for a range of diseases of the inner ear.

Cochlear implantation in the mouse via the round window: effects of array insertion

Animal models are the only means of assessing the effects of cochlear implantation (CI) at a cellular and molecular level. The range of naturally occurring and genetically-modified mouse strains which mimic human deafness provide excellent opportunities for auditory research. To date, there are very few studies of CI in mice. The main aims of this study were to develop a reproducible and viable technique to enable long term CI in the mouse and to assess the response of the mouse cochlea to implantation as a means of evaluating the success of the procedure. Electrode array implantation via the round window was performed in C57Bl/6 mice aged 3 and 6 months. The contralateral cochlea acted as a control. Auditory brainstem responses (ABR) were recorded prior to and following CI. Analysis showed greater threshold shifts in the implanted ear compared to the control ear post-implantation, but substantial preservation of hearing. There were no cases in which implantation caused a profound hearing loss across all frequencies. Cone beam computerised tomography and light microscopy confirmed correct placement of the electrode array within the scala tympani. Cochleae were prepared for histological examination. Initial analysis revealed encapsulation of the implant in tissue with morphological characteristics suggestive of fibrosis. Our results show that mouse CI via the round window offers a model for exploring tissue responses to implantation.

Molecular and cellular mechanisms of loss of residual hearing after cochlear implantation

OBJECTIVES

We describe the various molecular and cellular pathways that lead to early and delayed loss of residual hearing after cochlear implantation.

METHODS

We performed a systematic review using the Medline database with the key words cochlear implant, residual hearing, inflammation, apoptosis, and necrosis.

RESULTS

The mechanisms underlying the loss of residual hearing after cochlear implantation are multiple. Early hearing loss may be provoked by the surgical access to the inner ear spaces and by trauma caused by insertion of the electrode array. After the initial trauma, an acute inflammatory response promotes elevated levels of cytokines and reactive oxygen species, which in turn promote sensory cell loss by apoptosis, necrosis, and necrosis-like programmed cell death. Treatments that counteract such an inflammatory reaction, production of reactive oxygen species, and apoptosis are effective at preventing hair cell degeneration. However, delayed hearing loss appears to be a consequence of chronic inflammation with development of fibrotic tissue. The mechanisms that lead to fibrosis are poorly understood, and standard antiinflammatory drugs are insufficient for preventing its development.

CONCLUSIONS

Cochlear implantation is followed by an inflammatory response involving several pathways that lead to either short-term or long-term sensory hair cell degeneration. Future studies should focus on revealing the precise molecular mechanisms induced by cochlear implantation to allow the discovery of new targets for the effective prevention and treatment of loss of residual hearing.

Pre-, per- and postoperative factors affecting performance of postlinguistically deaf adults using cochlear implants: a new conceptual model over time

OBJECTIVE

To test the influence of multiple factors on cochlear implant (CI) speech performance in quiet and in noise for postlinguistically deaf adults, and to design a model of predicted auditory performance with a CI as a function of the significant factors.

STUDY DESIGN

Retrospective multi-centre study.

METHODS

Data from 2251 patients implanted since 2003 in 15 international centres were collected. Speech scores in quiet and in noise were converted into percentile ranks to remove differences between centres. The influence of 15 pre-, per- and postoperative factors, such as the duration of moderate hearing loss (mHL), the surgical approach (cochleostomy or round window approach), the angle of insertion, the percentage of active electrodes, and the brand of device were tested. The usual factors, duration of profound HL (pHL), age, etiology, duration of CI experience, that are already known to have an influence, were included in the statistical analyses.

RESULTS

The significant factors were: the pure tone average threshold of the better ear, the brand of device, the percentage of active electrodes, the use of hearing aids (HAs) during the period of pHL, and the duration of mHL.

CONCLUSIONS

A new model was designed showing a decrease of performance that started during the period of mHL, and became faster during the period of pHL. The use of bilateral HAs slowed down the related central reorganization that is the likely cause of the decreased performance.