Evaluation of round window accessibility to cochlear implant insertion

Hampshire Sheep as a Large-Animal Model for Cochlear Implantation

BACKGROUND

Sheep have been proposed as a large-animal model for studying cochlear implantation. However, prior sheep studies report that the facial nerve (FN) obscures the round window membrane (RWM), requiring FN sacrifice or a retrofacial opening to access the middle-ear cavity posterior to the FN for cochlear implantation. We investigated surgical access to the RWM in Hampshire sheep compared to Suffolk-Dorset sheep and the feasibility of Hampshire sheep for cochlear implantation via a facial recess approach.

METHODS

Sixteen temporal bones from cadaveric sheep heads (ten Hampshire and six Suffolk-Dorset) were dissected to gain surgical access to the RWM via an extended facial recess approach. RWM visibility was graded using St. Thomas' Hospital (STH) classification. Cochlear implant (CI) electrode array insertion was performed in two Hampshire specimens. Micro-CT scans were obtained for each temporal bone, with confirmation of appropriate electrode array placement and segmentation of the inner ear structures.

RESULTS

Visibility of the RWM on average was 83% in Hampshire specimens and 59% in Suffolk-Dorset specimens (p = 0.0262). Hampshire RWM visibility was Type I (100% visibility) for three specimens and Type IIa (> 50% visibility) for seven specimens. Suffolk-Dorset RWM visibility was Type IIa for four specimens and Type IIb (< 50% visibility) for two specimens. FN appeared to course more anterolaterally in Suffolk-Dorset specimens. Micro-CT confirmed appropriate CI electrode array placement in the scala tympani without apparent basilar membrane rupture.

CONCLUSIONS

Hampshire sheep appear to be a suitable large-animal model for CI electrode insertion via an extended facial recess approach without sacrificing the FN. In this small sample, Hampshire specimens had improved RWM visibility compared to Suffolk-Dorset. Thus, Hampshire sheep may be superior to other breeds for ease of cochlear implantation, with FN and facial recess anatomy more similar to humans.

Functional Hearing Preservation in Cochlear Implantation: The Miami Cocktail Effect

OBJECTIVE

To investigate if pharmacological treatment with prednisone and L-N-acetylcysteine (STE + NAC) influence functional hearing preservation in cochlear implant (CI) surgery.

STUDY DESIGNS

Preimplantation and postimplantation longitudinal case-control study.

SETTING

Tertiary referral center.

PATIENTS

Pediatric and adult recipients of CI with preimplantation functional hearing defined as an average of air-conducted thresholds at 125, 250, and 500 Hz (low-frequency pure-tone average [LFPTA]) <80 dB.

INTERVENTIONS

Preimplantation and postimplantation audiometry. Weight-adjusted oral prednisone and L-N-acetylcysteine starting 2 days before surgery (Miami cocktail). Prednisone was continued for 3 days and L-N-acetylcysteine for 12 days after surgery, respectively. Cochlear implantation with conventional length electrodes.

MAIN OUTCOME MEASURES

Proportion of patients with LFPTA <80 dB, and LFPTA change at 1-year postimplantation.

RESULTS

All 61 patients received intratympanic and intravenous dexamethasone intraoperatively, with 41 patients receiving STE + NAC and 20 patients not receiving STE + NAC. At 1-year postimplantation, the proportion of functional hearing preservation was 83% in the STE + NAC group compared with 55% of subjects who did not receive STE + NAC ( p = 0.0302). The median LFPTA change for STE + NAC-treated and not treated subjects was 8.33 dB (mean, 13.82 ± 17.4 dB) and 18.34 dB (mean, 26.5 ± 23.4 dB), respectively ( p = 0.0401, Wilcoxon rank test). Perioperative STE + NAC treatment resulted in 10 dB of LFPTA better hearing than when not receiving this treatment. Better low-frequency preimplantation hearing thresholds were predictive of postimplantation functional hearing. No serious side effects were reported.

CONCLUSION

Perioperative STE + NAC, "The Miami Cocktail," was safe and superior to intraoperative steroids alone in functional hearing preservation 1-year after cochlear implantation.

Round Window Visibility in Cochlear Implantation : Pre-operative Prediction Using Various Radiological Parameters

Purpose

The round window approach has become the most preferred route for electrode insertion in cochlear implant surgery; however, it is not possible at times due to difficult round window membrane (RWM) visibility. Our study aims to investigate the relationship between preoperative radiological parameters and the surgical visibility of the RWM in Cochlear implant patients.

Methodology

A prospective cross-sectional study of 31 patients, age < 6 years, with bilateral severe to profound sensorineural hearing loss was conducted at a tertiary care hospital. The preoperative HRCT temporal bone scan was studied, and the parameters evaluated were facial nerve location, facial recess width, and RWM visibility prediction. All patients were operated on via the posterior tympanotomy. The surgical RWM visibility was done after optimal drilling of the posterior tympanotomy recess. The relationship between the radiological parameters and surgical visibility of RWM was evaluated.

Results

The difference in the facial nerve location as per the type of RWM was found to be significant (p value < 0.05). However, the facial recess width was not significantly associated with RWM visibility. The radiological prediction of RWM visibility by tracing the prediction line over RWM was significantly associated with intraoperative RWM visibility.

Conclusion

The goal to look for preoperative scans is to predict the ease or difficulty of RWM visibility during surgery. The difficult visualization of the RWM, can result in dire intraoperative consequences. A comprehensive understanding of preoperative radiological parameters, coupled with meticulous surgical planning, is crucial to address these challenges effectively by focusing on enhancing RWM visualization.

Surgical anatomy of posterior tympanotomy: influence of the retrotympanum on round window exposure

OBJECTIVES

To describe how the retrotympanic structures could influence the visibility of the round window niche and the round window membrane during cochlear implant surgery, and to investigate if a round window approach is possible even in cases with unfavourable anatomy.

METHODS

Video recordings from 37 patients who underwent cochlear implantation were reviewed. The visibility of the round window niche and round window membrane at different timepoints was assessed according to a modified version of the Saint Thomas Hospital classification. The structures that concealed the round window niche and round window membrane were evaluated.

RESULTS

After posterior tympanotomy, 54 per cent of cases had limited exposure (classes IIa, IIb and III) of the round window niche. After remodelling the retrotympanum, round window niche visibility significantly increased, with 100 per cent class I and IIa cases. Following remodelling of the round window niche, visibility of more than 50 per cent of the round window membrane surface was achieved in 100 per cent of cases.

CONCLUSION

Remodelling the retrotympanum and the round window niche significantly increased exposure of the round window niche and round window membrane respectively, allowing round window insertion in all cases.

Endoscope-Assisted Cochlear Implantation in Atretic Round Window

Different techniques have been proposed for cochlear implant (CI) from its conventional transmastoid posterior tympanotomy approach. Endoscopy role in the otologic field is still relatively new, but it provides a better surgical view with improved image clarity, especially in the challenging anatomical visualization of the critical structures in CI surgery. A 3-year-old girl with bilateral progressive profound hearing loss was scheduled for left cochlear implant surgery. The pre-operative high-resolution computed tomography (HRCT) of the temporal bone and magnetic resonance (MR) of internal acoustic meatus reported no significant abnormality of the middle and inner ears structures bilaterally. The standard left postauricular cortical mastoidectomy and posterior tympanotomy were performed. However, the microscopic view could not visualize the round window (RW) niche despite a widened extended posterior tympanotomy and surgical field manipulation. Transfacial recess endoscopic examination was done and was able to identify the possibly atretic RW. With endoscopic guidance, CI electrodes were inserted via cochleostomy, and intraoperative impedance measurement and neural response telemetry were obtained both during surgery and the postoperative phase. No intra- and postoperative complications were observed in this case. Following activation, the CI was functioning well. In conclusion, atretic RW is a rare anomaly found intraoperatively during CI surgery. Endoscope-assisted electrode insertion offers excellent visualization of targeted middle ear structures, especially in limited or abnormal anatomy of RW, which could minimize the risk of surgical complications.

Various approaches to the round window for cochlear implantation: a systematic review

OBJECTIVE

Round window approaches are used to insert a cochlear implant electrode array into the scala tympani. This study aimed to review the literature to find the reported round window approaches.

METHOD

This review was performed according to the Preferred Reporting Items for Systematic Review and Meta-Analyses ('PRISMA') guidelines. Articles that described their surgical approach to the round window were included. The PubMed, Scopus, Web of Science and Cochrane Library electronic databases were searched through to June 2021. The study protocol was registered on Prospero (reference number: CRD42021226940).

RESULTS

A total of 42 reports were included. The following approaches were documented: the standard facial recess, keyhole, retrofacial, modified suprameatal, transaditus, combined posterior tympanotomy and endomeatal, modified Veria, canal wall down approaches, and endoscopically assisted technique.

CONCLUSION

This review suggested that there are numerous distinct round window approaches, providing alternatives when the round window is inaccessible through the standard facial recess.

Excursus in Chorda-Facial Angle Variation in Cochlear Implant Surgery: Cadaveric Temporal Bone Study

Facial recess approach through posterior tympanotomy is the most common & best appraoch for facilitating Cochlear Implant surgery through the round window. Sacrificing Chorda tympani nerve can be avoided by proper understanding of the anatomy of the Facial Recess & Chorda-Facial angles. Hence it is important to know the Chorda-Facial angle to prevent injury in Facial recess approach during Cochlear Implant surgery. Objective This study is done to know the Chorda-Facial angle variation with Round Window visibility during the Facial recess approach which is of relevance in Cochlear Implant surgery. Methods Thirty adult normal wet human cadaveric temporal bones were studied by performing by Posterior Tympanotomy & Facial Recess approach by using ZEISS microscope. Photographs were taken by digital camera of 26 megapixel, imported into computer, then Chorda-Facial angle were measured by Digimizer software & mean angle was calculated. Results The mean angle between the facial nerve & chorda tympani nerve was 20.232°. Bifurcation of chorda tympani nerve at the level of origin itself from the vertical segment of facial nerve was found in 6 Temporal bones out of 30. Round window visibility was noted in all 30 temporal bone specimens (100%). Conclusion The wide Chorda-Facial angle variations, especially the narrowest angle should be known to the otologist in particular to the Cochlear Implant surgeon, which may help avoid inadvertent damage to the CTN in facial recess approach during Cochlear Implant surgery & use diamond burr size of 0.6 mm or 0.8 mm.

A Study of Round Window and its Adjacent Anatomy to Guide the Cochlear Implant Electrode Insertion

Introduction

Residual hearing preservation has gained attention now which has brought round window membrane into the light, as a port for cochlear implantation. Atraumatic insertion of electrodes can be achieved by study of anatomical variations of round window and its forms which can guide the surgeon.

Objective

This study was undertaken to examine the anatomical variations of round window and its adjacent structures and their impact on surgical approach during cochlear implantation.

Methods

A series of 40 adult human temporal bones underwent high-resolution CT scanning and were further dissected for microscopic study of the round window.

Results

The antero posterior dimensions of RW ranged from 1.22 to 2.51 mm on radiology and on dissection 1.76 mm +/- 0.3 mm. Shape of round window in 72.5% of bones was oval, and in 27.5% bones it was round shaped. As per Saint Thomas hospital classification for Round window visualization we found 82.5% bones had type I RW visualization and 17.5% had type IIa RW visualization. Area of crista fenestra on dissection was ranging from 0.41 to 0.69 mm2.

Conclusion

Residual hearing preservation has become a new motto for surgeons. Therefore thorough anatomic knowledge of round window is must for careful insertion, as round window is closely related to the sensitive inner ear structures.

Cochlear Implantation: The use of OTOPLAN Reconstructed Images in Trajectory Identification

OBJECTIVES

This study aimed to define the best electrode trajectory line in cochlear implant (CI) surgery using the OTOPLAN (otology planning software) reconstructed 3D model and to investigate the surgical distance of the retro-facial approach as a direct access to the round window.

METHODS

Computed tomography (CT) scans of the normal temporal bone were included for analysis in this study. OTOPLAN reconstruction was used to build 3D models with specific ear structures for study analysis.

RESULTS

Twenty-five scans were included; the average age at the time of CT scan was 6.8±12 years. Twelve scans (48%) were right-sided and thirteen (52%) were left-sided. The best trajectory line to the round window was identified in all scans. The retro-facial approach was the optimal approach for 52% of cases (13/25). In all scans, the safe distance from the facial nerve were in favor of the retro-facial approach (P = 0.0011).

CONCLUSION

The OTOPLAN reconstructed imaging provided a good analysis of the retro-facial approach and helped in planning the surgical trajectory line towards the round window. Additionally, calculation of the surgical distance can help the surgeon compare the retro-facial approach to the standard facial recess for preoperative planning. These findings may help in robotic surgery.

Dimensions of the Posterior Tympanotomy and Round Window Visibility Through the Facial Recess: Cadaveric Temporal Bone Study Using a Novel Digital Microscope

To measure the width of the posterior tympanotomy in cadaveric temporal bones using the digital microscope and classify the round window visibility through it. In 17 cadaveric wet adult temporal bones, cortical mastoidectomy followed by posterior tympanotomy was performed, delineating the facial and chorda tympani nerves. Antero-posterior width of the facial recess was measured at the levels of oval window and round window with the help of a digital microscope and its software. Visibility of the round window through the facial recess was assessed and classified according to the St. Thomas Hospital classification. The mean antero-posterior width of the facial recess measured was 4.7 ± 0.6 mm at the level of oval window and 4.3 ± 0.7 mm at the level of round window. Round window visibility grading in bones studied were as follows-Type 1 (53%), Type 2a (24%), Type 2b (18%) and Type 3 (5%). Interobserver variability of the posterior tympanotomy measurements using the digital microscope was found to be 91.1% with a 95% confidence interval of 79 to 97% at the level of oval window and 94.1% with a 95% confidence interval (CI) of 87 to 98% at the level of round window. The visibility of the round window is not entirely dependent on the facial recess width at the round window level, suggesting that other factors like cochlear rotation may also contribute to its actual location. Measurements of micro distances with the help of digital microscope seems to be convenient, cost effective and accurate with good inter observer reliability.

Anatomical Variations, Surgical Difficulties, and Complications Associated with Cochlear Implantation in Different Age Groups of the Pediatric Population of Nepal: A Tertiary Level Hospital-Based Study

Pediatric cases account for the major proportion of the population for whom cochlear implantation is indicated. This study aims to review the anatomical variations, surgical difficulties, and complications associated with cochlear implantation surgery in different age groups of the pediatric population of Nepal.This study was conducted at Tribhuvan University Teaching Hospital, Nepal. A prospectively set data of cases who underwent cochlear implantation between January 2015 and March 2020 were analyzed for details of surgical procedure, surgical difficulties, and intraoperative and postoperative complications. The anatomical variations encountered during surgery were classified as: developmental anomalies, round window niche variations and acquired abnormalities resulting from inflammation. Intraoperative surgical difficulties were defined based on the operating surgeon's perspective. Complications following cochlear implantation were classified as surgical and nonsurgical or device-related. We used SPSS version 25 for the analysis of our data. Chi-square test and Fisher's exact test were used to analyze the statistical association.The most commonly encountered difficulty was the requirement of an extended posterior tympanotomy approach due to poor visualization of round window niche. There was a statistically significant association of difficult insertion of electrodes with round window niche visibility. The common complications encountered were intraoperative facial nerve exposure, bleeding, electrode-related problems, cerebrospinal fluid gusher, and device failure.Cochlear implantation with an experienced surgeon in pediatric population is a relatively safe procedure. There is no association of the difficulties and complications related to surgery with the different age groups.

The Impact of the Location of Chorda Tymapni Nerve Origin on the Round Window Accessibility During Pediatric Cochlear Implantation: A Radioclinical Assessment

OBJECTIVES

This study assessed the impact of the location of the chorda tympani nerve (CTN) origin on the round window (RW) accessibility during pediatric cochlear implantation (CI). We also tried to validate the radiologic method to measure the length between the origin of the CTN from the facial nerve to the stylomastoid foramen (CF-SM).

STUDY DESIGN

It was a prospective observational case-series study.

SETTINGS

The included CI surgeries were performed at tertiary referral institutions from November 2018 to August 2021.

SUBJECTS

We included 146 pediatric patients who were candidates for CI.

INTERVENTION

We measured the CF-SM length in the parasagittal cut of the preoperative high-resolution computed tomography. We also classified the intraoperative RW according to the accessibility through the ordinary posterior tympanotomy approach into accessible or inaccessible.

MAIN OUTCOME MEASURE

We correlated the preoperative radiologic CF-SM length with the intraoperative RW accessibility.

RESULTS

The radiologic CF-SM length ranged from 2.9 to 7.4 mm with a mean of 4.9 ± 1.03 mm. The RW was accessible in 107 patients and inaccessible in 39 patients. Spearman's correlation coefficient revealed a significant relationship between the location of CTN origin and the RW accessibility as the p value was less than 0.0001.

CONCLUSIONS

We found a precise method to measure the CF-SM length in the parasagittal cut of the high-resolution computed tomography. We also found a significant impact of the location of the CTN origin on intraoperative RW accessibility. The radiologic CF-SM length of more than 5.4 mm had a powerful prediction capability of the RW inaccessibility.

The role of the endoscope in cochlear implantation. A systematic review

OBJECTIVE

To review the role of the endoscope in cochlear implantation (CI).

METHODS

MEDLINE, ScienceDirect, Google Scholar and the Cochrane Library databases as well as other sources were searched by two independent reviewers. Studies including patients undergoing either exclusively endoscopic or endoscopic ally assisted CI were eligible for inclusion. Endoscopic CI approaches and postoperative complications were the primary outcomes. Secondary endpoints included the degree of round window (RW) microscopic visualization according to St Thomas' Hospital classification as well as type of cochleostomy for electrode insertion in the scala tympani (ST).

RESULTS

Fourteen studies met the inclusion criteria comprising 191 endoscopic or endoscopically assisted CI cases. The endoscope was used for better visualization of the RW across all included studies, facilitated the insertion of the electrode in the ST and spared a mastoidectomy in a number of cases. No facial nerve palsy was reported in any of the studies. The most common complication was external auditory canal/ tympanic membrane tear followed by chorda tympani injury.

CONCLUSION

The microscopic CI approach is still the gold standard. The endoscope facilitates the recognition of the RW area and leads to successful and safe implantation particularly in difficult anatomical scenarios, ear malformations and advanced otosclerosis. Endoscopically assisted CI procedures offer the opportunity to avoid a posterior tympanotomy and reduce the risk of facial nerve injury. To date, the lack of long term data does not permit the widespread adoption of completely endoscopic CI procedures without a mastoidectomy.

Combined Endoscopic/Microscopic Cochlear Implantation Through the Oval Window

Standard round window (RW) cochlear implantation is a well-described technique. Implantation might be difficult in patients with inner and middle ear anomalies, in some cases because of not achieving adequate exposure to the RW, with a related higher risk of complications such as facial nerve injury. It is proposed a combined microscopic/endoscopic oval window approach in a 63 year old man affected by bilateral Menière disease, with bilateral severe sensorineural hearing loss, speech discrimination score for bysillabic words under 40% and a hidden RW by anomalous facial nerve course. All electrodes entered the cochlear with good freefield thresholds and auditory ability results. A partial marginalis nerve palsy occurred at the second postoperative day and completely reversed at 2 months from surgery. Endoscopicassisted oval window cochlear implantation may be a safe alternative surgical technique in cases where surgeons are not able to access RW.

Radiological classification of the mastoid portion of the facial nerve: impact on the surgical accessibility of the round window in cochlear implantation

BACKGROUND

Mastoid portion of the facial nerve plays an important role in the round window approach of cochlear implantation.

OBJECTIVES

This study aimed to predict the anterior displacement of the mastoid portion of the facial nerve in the preoperative HRCT coronal cuts. We also aimed to detect the implication of anterior displacement of MPFN on the R.W. accessibility through the posterior tympanotomy during cochlear implantation.

MATERIALS AND METHODS

It was a retrospective observational cohort study in tertiary referral hospitals. We included 246 pediatric patients who underwent cochlear implantation due to bilateral severe to profound SNHL through a posterior tympanotomy approach.

RESULTS

Type I MPFN was present in 84 cases, type II MPFN was present in 149 patients, and type III MPFN was present in 13 cases. R.W. was inaccessible in 3 cases with MPFN type II and in 11 subjects with MPFN type III. There was a statistically significant difference regarding the R.W. accessibility between the three types of MPFN (p-value <.05). There was a strong statistically significant correlation between R.W. accessibility and the radiological type of the MPFN.

CONCLUSION

Mandour radiological classification of the mastoid portion of the facial nerve in the preoperative HRCT coronal offers an easily applicable method to detect the anterior displacement of the facial nerve by using easy and well-known landmarks. This classification can also predict R.W. accessibility through posterior tympanotomy during cochlear implantation with 97.97% accuracy.

Determination of the Round Window Niche Anatomy Using Cone Beam Computed Tomography Imaging as Preparatory Work for Individualized Drug-Releasing Implants

Modern therapy of inner ear disorders is increasingly shifting to local drug delivery using a growing number of pharmaceuticals. Access to the inner ear is usually made via the round window membrane (RWM), located in the bony round window niche (RWN). We hypothesize that the individual shape and size of the RWN have to be taken into account for safe reliable and controlled drug delivery. Therefore, we investigated the anatomy and its variations. Cone beam computed tomography (CBCT) images of 50 patients were analyzed. Based on the reconstructed 3D volumes, individual anatomies of the RWN, RWM, and bony overhang were determined by segmentation using 3D Slicer^TM with a custom build plug-in. A large individual anatomical variability of the RWN with a mean volume of 4.54 mm³ (min 2.28 mm³, max 6.64 mm³) was measured. The area of the RWM ranged from 1.30 to 4.39 mm² (mean: 2.93 mm²). The bony overhang had a mean length of 0.56 mm (min 0.04 mm, max 1.24 mm) and the shape was individually very different. Our data suggest that there is a potential for individually designed and additively manufactured RWN implants due to large differences in the volume and shape of the RWN.

Surgical approach to the facial recess influences the acceptable trajectory of cochlear implantation electrodes

PURPOSE

To provide practical guidance to the operative surgeon by mapping the location, where acceptable straight-line virtual cochlear implant electrode trajectories intersect the facial recess. In addition, to investigate the influence of facial recess preparation, virtual electrode width and surgical approach to the cochlea on these available trajectories.

METHODS

The study was performed on imaging data from eight cadaveric temporal bones within the University of Melbourne Virtual Reality (VR) Temporal Bone Surgery Simulator. The facial recess was opened to varying degrees, and acceptable trajectory vectors with varying diameters were calculated for electrode insertions via cochleostomy or round window membrane (RWM). The percentage of acceptable insertion vectors through each location of the facial recess was visually represented using heatmaps.

RESULTS

Seven of the eight bones allowed for acceptable vector trajectories via both cochleostomy and RWM approaches. These acceptable trajectories were more likely to lie superiorly within the facial recess for insertion via the round window, and inferiorly for insertion via cochleostomy. Cochleostomy insertions required a greater degree of preparation and skeletonisation of the junction of the facial nerve and chorda tympani within the facial recess. The width of the virtual electrode had only marginal impact on the availability of acceptable trajectories. Heatmaps emphasised the intimate relationship the acceptable trajectories have with the facial nerve and chorda tympani.

CONCLUSION

These findings highlight the differences in the acceptable straight-line trajectories for electrodes when implanted via the round window or cochleostomy. There were notable exceptions to both surgical approaches, likely explained by the variation of hook region anatomy. The methodology used in this study holds promise for translation to patient specific surgical planning.

Radiological and surgical aspects of round window visibility during cochlear implantation: a retrospective analysis

Purpose

The round window approach has become the most preferred option for cochlear implant (CI) insertion, however, sometimes it may not be possible due to the (in)visibility of the round window membrane (RWM). We addressed the prevalence, consequences and indicators of difficult detection of the RWM in cochlear implant surgery.

Methods

This study retrospectively analysed the operative reports and preoperative high resolution axial-computed tomography (CT) scans of a consecutive cohort of patients who underwent a CI insertion. The main outcomes were surgical outcomes of the RW approach, and assessment of radiological markers.

Results

The operative reports showed that RWM insertion was feasible in 151 out of 153 patients. In 18% of the patients the RWM was difficult to visualize. All these patients had at least one intraoperative event. The chorda tympani nerve (CTN) or posterior canal wall was affected in 8% of the 153 patients and the fallopian canal in 6%. These patients had a facial-chorda tympani nerve distance on the CT scan that was considerably smaller than normal patients (1.5 mm vs 2.3 mm). In addition, a prediction line towards the anterolateral side of the RWM was found to be more prevalent in these patients’ CT scans (sensitivity 81%, specificity 63%).

Conclusion

The RW approach is feasible in almost all patients undergoing CI surgery. Difficult visualisation of the RWM seems to lead to at least one intraoperative event. Radiological measures showed that these patients had a smaller facial recess and a more anteriorly placed facial nerve, which can be used to better plan a safe insertion approach.

The role of high-resolution Computer Tomography in prediction of the round window membrane visibility and the feasibility of the round window electrode insertion

OBJECTIVE

The aim of this work is to assess the role of pre-operative high-resolution computerized tomography (HRCT) in prediction of the round window membrane (RWM) visibility and the feasibility of round window electrode insertion.

MATERIALS AND METHODS

Retrospective study on a series of 97 cases of cochlear implant (CI) who were implanted in tertiary referral centers. We reviewed HRCT of all cases, and we implicated two radiological measurements on HRCT which are membrano-facial angle (MFA) and length of the bony overhang of the round window niche (RWN). We reviewed the intra-operative surgical video recordings of all cases for detection of the type of RWM visibility, according to The St Thomas' Hospital classification.

RESULTS

The MFA was 21.9 ± 14.5. The length of the bony overhang of the RWN was 2.4 ± 0.33 mm. About 37% of the studied patients needed cochleostomy. The best cut-off of MFA in the prediction of the RW (type 2B and 3) was ≥ 15.1o with sensitivity 100%, and specificity 82%.

CONCLUSION

HRCT offers highly reliable and reproducible measurements for the prediction of RWM visibility and, therefore, prediction of the utility of the RW approach for electrode insertion. Membrano-facial angle (MFA) is a new measurement that can be used for this purpose.

Radiologic anatomy of the round window relevant to cochlear implantation and inner ear drug delivery

Objective

To determine anatomic relationships and variation of the round window membrane to bony surgical landmarks on computed tomography.

Study design

Retrospective imaging review.

Methods

100 temporal bone images were evaluated. Direct measurements were obtained for membrane position. Vector distances and angulation from umbo and bony annulus were calculated from image viewer software coordinates.

Results

The angle of round window membrane at junction with cochlear basal turn was (42.1 ± 8.6)°. The membrane's position relative to plane of the facial nerve through facial recess was (14.7 ± 5.2)° posterior from a reference line drawn through facial recess to carotid canal. Regarding transtympanic drug delivery, the round window membrane was directed 4.1 mm superiorly from the inferior annulus and 5.4 mm anteriorly from the posterior annulus. The round window membrane on average was angled superiorly from the inferior annulus (77.1 ± 27.9)° and slightly anteriorly from the posterior annulus (19.1 ± 11.1°). The mean distance of round window membrane from umbo was 4 mm and posteriorly rotated 30° clockwise from a perpendicular drawn from umbo to inferior annulus towards posterior annulus. Together, these measurements approximate the round window membrane in the tympanic membrane's posteroinferior quadrant.

Conclusions

These radiologic measurements demonstrate normal variations seen in round window anatomy relative to facial recess approach and bony tympanic annulus, providing a baseline to assess round window insertion for cochlear implantation and outlines anatomic factors affecting transtympanic drug delivery.

Anatomical Correlates and Surgical Considerations for Localized Therapeutic Hypothermia Application in Cochlear Implantation Surgery

Application of localized, mild therapeutic hypothermia during cochlear implantation (CI) surgery is feasible for residual hearing preservation.

Predicting round window visibility by HRCT during cochlear implantation in children

Objective: The present study aimed to radiologically evaluate the visibility of round window during cochlear implantation by high-resolution computed tomography (HRCT) imaging of temporal bone. Study design: This was a cross-sectional descriptive analytic study. Methods: Two new radiologic measurements were evaluated on the presurgical HRCT of temporal bone, including (1) the angle between the line parallel to coronal axis that passes through the middle of the round window niche (RWN) and the line that connects the anterior portion of facial nerve (FN) to the middle of the RWN (RWN angle) and (2) the vertical distance between this coronal plane and the anterior portion of the FN, modified facial recess distance (MFRD). The measurements were then compared with the visibility of the round window (RW) during operation, as reported by the surgeon. Result: The present study compared the abovementioned CT scan findings of cochlear implanted children in visible (n = 21) and nearly invisible (n = 21) RW during surgery, as reported by the surgeon. The analysis revealed that both MFRD (P < 0.01) and RWN angle (P < 0.04) were significantly different between the two groups. Conclusion: the RWN angle and MFRD are fairly reliable predictors of round window visibility during cochlear implantation.

Round window accessibility during cochlear implantation

OBJECTIVE

To assess data regarding round window (RW) visibility and surgical approaches in cochlear implant cases, and to describe and analyze surgical steps relevant for the RW approach in cochlear implantation.

STUDY DESIGN

Prospective clinical study.

METHODS

A questionnaire was completed by surgeons after each of altogether 110 cochlear implantations. Round window membrane (RWM) visibility was graded according to the St Thomas Hospital (STH) classification.

RESULTS

Performing different surgical steps during the preparation of the RW niche, the RWM could be fully exposed (STH Type I) in 87%. A RW approach could be used for electrode insertion in 89% of the adult and 78% of the pediatric cases. The distribution of RW types differed significantly between adults and children. Drilling of the superior bony lip was the surgical step most frequently needed in adult as well as pediatric cases to obtain optimal RW exposure.

CONCLUSION

In children, optimized surgical exposure of the RW niche resulted in only 52% full RWM visibility; whereas in adults, this could be achieved in 87%. The facial nerve (FN) had to be exposed at the level of the posterior tympanotomy in more than 70% of pediatric cases with full RWM visibility; while in adult cases with 100% visibility, such specific exposure was necessary in only 33%. Thus, surgical preparation of the RW niche seems to be more demanding in children than in adults.

Location of the stapedius muscle with reference to the facial nerve in patients with unilateral congenital aural atresia: implication for active middle ear implants surgery

Background: Detailed investigations of the stapedial muscle (SM) in congenital aural atresia (CAA) patients have yet to be adequately conducted.Objectives: To assess image variations in the mastoid segment of the facial nerve (FN) and SM in CAA.Materials and methods: A total of nine patients comprising of 9 ears with unilateral CAA were studied. The courses of the FN and SM were evaluated from the basic point to 1 mm intervals between the mastoid portion of FN, and measured from the mean X and Y values in each group.Results: The atresia side of FN among the Y values showed significant differences compared to the contralateral side. In terms of the SM, there were no significant differences in both the X and Y values. The stapedial muscle of the CAA patients was located medially to the FN. Conversely, the distance from the PSC to the FN revealed no significant differences with regard to the X and Y values for each group.Conclusion: The current observations revealed that the SM is located more posterior to the FN in CAA patients, and this is mainly attributed to the laterally and anteriorly displaced FN.

Anatomy of the Round Window Region With Relation to Selection of Entry Site Into the Scala Tympani

OBJECTIVES/HYPOTHESIS

The aim of cochlear implantation is to safely insert an electrode array into the scala tympani (ST) while avoiding damage to surrounding structures. There is disagreement on the optimal way of entering the ST-the round window (RW) approach versus cochleostomy. Regardless of the chosen approach, it is vital to understand the regional anatomy, which is complex, difficult to conceptualize, and rarely dissected in temporal bone courses. The goal of this study was to examine the anatomy of the RW to gain more in-depth knowledge on the local relationships of the anatomical structures and propose an approach for entering the ST in cochlear implant surgery tailored to the encountered anatomy.

STUDY DESIGN

Cadaveric prevalence study and expert opinion with literature review.

METHODS

Cadaveric temporal bone dissection (n = 13) by the first author assessing the RW anatomy.

RESULTS

The round window membrane (RWM) and the osseous spiral lamina (OSL) are curved structures, each with a horizontal and a vertical part. The two horizontal portions are very closely apposed. The relationship between the OSL and the RWM determines the best site for a cochleostomy, which if required is best placed anteroinferiorly to the RWM. The distance between the oval window inferior margin and the RW membrane is less than 2 to 3 mm. The ST initially extends inferiorly and medially to the RW.

CONCLUSIONS

The findings of our dissection have implications for cochlear implant surgery in aiming to avoid trauma to the OSL and basilar membrane and aid decision making in choosing the safest surgical approach.

LEVEL OF EVIDENCE

5. Laryngoscope, 131:E598-E604, 2021.

Endoscopic visualisation of the round window during cochlear implantation

Background

Endoscopes provide a magnified view of the middle ear and visualisation of hidden areas. Otoendoscopes facilitate excellent visualisation of the round window niche during cochlear implantation.

Objective

To compare microscopic and endoscopic visualisation of the round window membrane during cochlear implantation in 20 patients.

Methods

Twenty patients who underwent cochlear implantation were included in the study. After maximum exposure of the round window, the accessibility of the round window membrane was graded according to the St Thomas Hospital classification, first by microscope and then by endoscope.

Results

With the use of the endoscope, visualisation of the round window membrane improved in all the patients as compared to the microscope. The electrode array was inserted via a round window or extended round window approach in all but two cases; the latter cases required bony cochleostomy because of unfavourable anatomy.

Conclusion

The main benefit of endoscope-assisted cochlear implantation is improved visibility of the round window region.

Endoscopic approach to the round window through posterior tympanotomy for cochlear implantation in children: A study on feasibility

OBJECTIVE

To demonstrate the feasibility of rigid endoscopy through posterior tympanotomy, which provides both a view of the round window and direction of the scala tympani in children.

METHODS

After a standard mini-invasive surgical approach with postauricular access and transmastoid posterior tympanotomy of 2 mm, a 0°, 1.9 mm diameter and 11 cm long endoscope is positioned in proximity of the upper part of the posterior tympanotomy to obtain a panoramic view of the inferior part of the medial wall of the tympanic cavity. Surgical complications and changes in hearing threshold were analyzed.

RESULTS

Eight children were submitted to cochlear implantation with endoscopic assistance through posterior tympanotomy. Complete visualization of the round window niche was possible in every ear. No complications related to the procedure were observed. Preoperative threshold was preserved in 9 of 10 ears.

CONCLUSIONS

Direct endoscopic view through the posterior tympanotomy allows visualization of the entire round window niche as well as the angle of introduction of the multi-electrode array along the direction of the scala tympani.

Round window membrane visibility related to success of hearing preservation in cochlear implantation

Objectives: This study was designed to evaluate the relationship between the degree of round window membrane (RWM) exposure and hearing outcome. Materials and methods: Forty-six ears with cochlear implantation (CI) were enrolled. The degree of RWM exposure was divided into Grade I (<25%), Grade II (25-50%), and Grade III (>50%). The hearing outcomes were evaluated at 1.5 and 12 months postoperatively. Results: Twenty-seven ears were Grade I, 13 were Grade II, and 6 were Grade III. RW approach was used in all ears of Grades II and III and 20 ears of Grade I and cochleostomy was used in 7 ears of Grade I. The pattern of bony overhang was multidirectional in 41 ears. Threshold shift significantly decreased proportional to the increase of RWM exposure after CI. The mean RWM exposure was 32.1 ± 24.4% in ears with more than partial preservation (n = 17), and 13.3 ± 11.7% in the other ears (n = 6) at 12 months post-CI (p = .061). Age at CI differed significantly between ears that had more than partial preservation and the other ears at 1.5 months post-CI. Conclusions and significance: Degree of RWM exposure and age at CI might be factors predicting hearing outcome after CI using the RW approach.

Comparative evaluation of round window niche accessibility pre-operatively on high-resolution computed tomography of the temporal bone with intra-operative findings

Objective

To compare round window niche visibility as seen endoscopically during cochlear implant surgery with pre-operative high-resolution computed tomography of the temporal bone.

Methods

Nineteen patients scheduled for cochlear implantation, aged 2–20 years, were referred for computed tomography from October 2016 to March 2018. Angles were measured between the lines passing through the mid-sagittal plane and cochlear basal turn on the scans. Endoscopic round window niche visibility during posterior tympanotomy was categorised as: type I = 100 per cent, type IIa = more than 50 per cent, type IIb = less than 50 per cent or type III = 0 per cent. Pre-operative computed tomography measurements were used to predict round window niche visibility before surgery and correlated with intra-operative findings.

Results

The mean (range) of pre-operative angles on computed tomography for endoscopic visibility types I, IIa and IIb, were 64.06° (61.16–69.37°), 63.81° (58.61–71.35°) and 56.48° (50.37–59.05°), respectively, a statistically significant finding (one-way analysis of variance test, p = 0.016).

Conclusion

Pre-operative high-resolution temporal bone computed tomography measurements are useful in predicting round window niche visualisation as viewed endoscopically during posterior tympanotomy. The angle was more acute in type IIb compared to type I.

Endoscopic-Assisted Cochlear Implantation in Children with Malformed Ears

OBJECTIVE

Complex middle and inner ear malformations are considered an important limitation for cochlear implant (CI) with traditional microscopic techniques. The aim of the present study is to describe the results of the endoscopic-assisted CI procedure in children with malformed ears.

STUDY DESIGN

Case series with chart review of consecutive patients.

SETTING

Two tertiary referral centers: University Hospital of Verona and University Hospital of Modena, Italy.

SUBJECTS AND METHODS

In total, 25 children underwent endoscopic-assisted cochlear implantation between January 2013 and January 2018. The audiologic and neuroradiologic assessment showed profound hearing loss and malformation of the middle and inner ear in all children. A complete review of anatomic features, surgical results, and audiologic outcomes was performed. The surgical technique is described step-by-step, and the outcomes are detailed.

RESULTS

All patients (mean age, 3.6 years; range, 2.8-9 years) underwent a transattical/endoscopic-assisted CI procedure. All children showed varying degrees of auditory benefit, as measured by routine audiometry, speech perception tests, and Categories of Auditory Performance scores (mean, 6). No immediate or late postoperative complications were noted.

CONCLUSION

The endoscopic-assisted approach proved to be successful in cochlear implantation. The direct visualization and magnification allow (1) exploration of the tympanic cavity; (2) confirmation of all anatomic features, with strict control of the course of the facial nerve, round window area, and inner ear; and (3) performance of the cochleostomy with adequate insertion of the array.

Predictors of round window membrane visibility in pediatric cochlear implant surgery using temporal bone HRCT: A retrospective study

OBJECTIVE

To predict round window membrane (RWM) visibility and electrode insertion sites using high-resolution computed tomography (HRCT) in pediatric cochlear implant surgery.

MATERIALS AND METHODS

Sixty-two ears of 36 infants less than 1 year old were included in our study. Intraoperative RWM visibility was classified into three types corresponding to three different surgical approaches. Radiologic parameters were measured on preoperative axial temporal HRCT images and correlated with RWM visibility and surgical approaches.

RESULTS

A significant correlation was found between the degree of RWM visibility and the following two parameters: 1) a line (l_w) was drawn from the posterior margin of the RWM to the intersection point of the posterior wall of the external auditory canal (EAC) and mastoid cortex. Another line (l_f) was drawn between the posterior margin of the RWM and the lateral margin of the FN. The angle between l_w and l_f was measured as angle A, P < 0.01, R² = -0.809; 2) a line (l_m) was drawn from the anterior to posterior margin of the RWM, and the angle between l_m and l_f was measured as angle B, P < 0.01, R² = -0.850. A nonsignificant correlation was found between the degree of RWM visibility and the facial recess width, p > 0.05, R² = -0.00015.

CONCLUSION

RWM visibility showed a high correlation with the two angular measurements (angle A and angle B) and was associated with electrode insertion sites. In children less than one year old, surgeons can depend on those two parameters in predicting the RWM visibility.

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.

Access to Round Window Niche via Posterior Tympanotomy and Impact of Drilling Its Overhangs: A Cadaveric Descriptive Study

We intended to study the morphological parameters of round window region and assess the gain in exposure achieved by drilling the round window niche overhang. The Exposure of the round window membrane (RWM) is of prime importance to carry out atraumatic electrode insertion for cochlear implantation. The anatomy of round window has been a subject of considerable debate in literature. Fifty-one Formalin preserved adult cadaveric temporal bones were micro-dissected to carry out an 'optimal' posterior tympanotomy to expose the round window region. The bony overhangs of round window niche (RWN) were next drilled to achieve maximal possible exposure the RWM without violating the annulus of the same. The exposure was classified as per St Thomas' Hospital classification. The round window could not be visualized in 3 bones (5.9%). The commonest morphology of RWN was dome shaped, found in 18 (37.5%) and that of the RWM was oval shaped, found in 14 (29.2%) bones. Pre drilling 41 bones had a > 50% exposure of RWM while post drilling > 50% exposure could be achieved in all the bones except the 3 bones in which RWN could not be visualized to begin with. The drilling of the RWN overhangs exposed RWM in entirety in 91.7% of bones with a visible morphology of RWN pre drilling. RWN and RWM exhibit varied morphology. Drilling of the round window niche overhangs can considerably enhance the exposure of RWM.

Endoscope-Assisted Cochlear Implantation

OBJECTIVES

Our aim was to present our endoscope-assisted cochlear implantation (CI) technique, in which the middle ear landmarks were identified through the facial recess exposure by using an endoscopic view without elevating the tympanic annulus. The secondary goal was to assess whether the situation of difficult surgical exposure could be predicted by evaluating preoperative axial computed tomography (CT) examinations.

METHODS

CT examinations and surgical outcomes of endoscope-assisted CI surgeries were analyzed.

RESULTS

A total of 179 CI operations performed in 27 adults (15.1%) and 152 children (84.9%) were retrospectively evaluated. It was found that in 14 cases (7.8%), endoscopic examination contributed substantially in identifying the round window (RW) membrane correctly. Endoscopic identification of the RW through the posterior tympanotomy enabled us to perform a straightforward surgery in all these cases, without the need for switching to a bony cochleostomy or alternative surgical techniques. The difficulty in the surgical exposure was predicted preoperatively by examining the axial CT scans in six of the 14 cases (42.8%) for which endoscopic assistance was necessary in order to identify the RW correctly.

CONCLUSION

The main benefit of endoscope-assisted CI is the improved visibility leading to a panoramic view of the RW region. The implementation of transfacial recess endoscopic examination into the conventional CI technique is helpful to avoid problems during surgical orientation. However, the difficulty in the surgical exposure of the RW cannot be reliably predicted by the subjective evaluation of preoperative CT scans and more studies are needed to obtain reliable criteria.

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 Anatomy of the Human Round Window Region: Implication for Cochlear Endoscopy Through the External Auditory Canal

OBJECTIVE

To enable development of an endoscope for cellular-level optical imaging of the inner ear.

STUDY DESIGN

A prospective study of 50 cadaveric human temporal bones to define detailed surgical anatomy of the round window (RW) region and the range of angles necessary to reach the RW membrane perpendicularly via the external ear canal.

MAIN OUTCOME MEASURE

The transcanal angle to the RW membrane was surgically measured in 3D intact specimens, and correlated with the angle calculated from temporal bone computed tomography (CT) scans of the same specimens obtained before and after measurements in situ.

RESULTS

Surgically measured transcanal angles to the RW membrane correlated well with the radiographically measured angles. The angles ranged from 110 to 127 degrees, with the median of 115 degrees and the middle 50% ranging from 109 to 119 degrees. Four temporal bones were excluded because of pathology. The opening of the RW niche was located posteriorly in six bones (13%), inferiorly in 18 bones (39%), and postero-inferiorly in 22 bones (48%). The angles were not statistically different among the three orientations of the RW niche.

CONCLUSIONS

By correlating measurement from cadaveric human temporal bones and their CT scans, we defined key parameters necessary for designing an endoscope for intracochlear imaging using a minimally invasive approach through the external auditory canal. The excellent correlation between the measurement on the CT scan and the actual shape of the probe that was able to reach the RW through the ear canal enables selection of the probe using the CT data.

The Crista Fenestra and Its Impact on the Surgical Approach to the Scala Tympani during Cochlear Implantation

Objective: The aim of this work was to describe the dimensions of the crista fenestra and determine its presence by means of high-resolution computed tomography (CT) for the purpose of cochlear implantation via the round window approach. Methods: A series of 10 adult human temporal bones underwent high-resolution CT scanning and were further dissected for microscopic study of the round window niche. Results: In all of the specimens, the round window membrane was fully visualized after the complete removal of bony overhangs. The crista fenestra was identified as a sharp bony crest located in the anterior and inferior borders of the niche; its area ranged from 0.28 to 0.80 mm2 (mean 0.51 ± 0.18). The proportion of the area occupied by the crista fenestra in the whole circumference of the round window ranged from 23 to 50% (mean 36%). We found a moderate positive correlation between the area of the niche and the dimensions of the crista fenestra (Spearman rho: 0.491). In every case, high-resolution CT scanning was unable to determine the presence of the crista fenestra. Conclusion: The crista fenestra occupies a variable but expressive area within the bony round window niche. Narrower round window niches tended to house smaller crests. The presence of the crista fenestra is an important obstacle to adequate access to the scala tympani. Nevertheless, a high-resolution CT scan provides no additional preoperative information with regard to its presence for the purpose of surgical access to the scala tympani via the round window niche.

Revisiting the Anatomy of the Facial Recess: The Boundaries of the Round Window Exposure

BACKGROUND

The exposure of the round window (RW) through the facial recess (FR) is sometimes partial. The anatomic variations that alter RW exposure during cochleostomy have not been clearly defined to date.

AIMS

The aim of this study was to assess the best FR position in which to achieve the widest exposure of the RW niche and to define the topographic relationship between two other important anatomical structures, the facial nerve (FN) and the chorda tympani (CT).

STUDY DESIGN

Cadaver study.

METHODS

Twenty-four temporal bones were included in the study. Anterior and posterior epitympanectomy and posterior tympanotomy were performed after mastoidectomy. Bone was removed until the FN and CT were skeletonized and the CT branching point was visible. Two pictures were taken. The first was taken when the facial recess was at its widest exposure, while the second was taken when the RW niche was maximally exposed through the facial recess. Various measurements were taken.

RESULTS

The RW niche was totally visible in 19 temporal bones (79.2%). The RW was partially visible in the remaining five bones (20.8%). The unexposed part of the RW lay posteromedial to the FN in these five bones. While the branching point of the CT could be visualized in all cases at the widest exposure of RW, the part of the FN distal to the branching point was hidden in eight subjects (33.3%) under the posterior wall of the external ear canal.

CONCLUSIONS

The RW niche was totally visible in most of the temporal bones. The RW lay posteromedial to the FN in some cases and total exposure was impossible.

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.