Topographical relationships among the facial nerve, chorda tympani nerve and round window with special reference to the approach route for cochlear implant surgery

Cochlear Apex Triangulation Utilizing Ct Measures And Middle Ear Landmarks

Objective

To better characterize the cochlear apex in relation to surgically relevant landmarks to guide surgeons and improve procedural success of apical electrode placement.

Study Design

Retrospective image analysis.

Setting

Tertiary referral center.

Patients

Cochlear implant recipients with available preoperative computed tomography (CT) imaging.

Intervention

None.

Main Outcome Measure

Cochlear dimensions and cochlear apex distance measures to surgically relevant middle ear landmarks and critical structures.

Results

Eighty-two temporal bone CT scans were analyzed utilizing multiplanar reformats. The average lateral width of promontory bone over the cochlear apex was 1.2 mm (standard deviation [SD], 0.3). The anteroposterior distance from the round window (avg, 4.2 mm; SD, 0.5), oval window (avg, 3.3 mm; SD, 0.3), cochleariform process (avg, 2.3; SD, 0.5), and superior-inferior distance from the cochleariform process (avg, -0.9; SD, 0.8) to the cochlear apex were measured. The relationship of the cochlear apex to critical structures was highly variable.A newly developed stapes vector was created and found to mark the posterior/superior boundary of the apex in 94% of patients. When a vector parallel to the stapes vector was drawn through the round window, it marked the anterior/inferior boundary of the cochlear apex in 89% of patients.

Conclusions

This study assists in characterizing cochlear apex anatomy and its relation to surrounding structures as a means of improving procedural accuracy and reducing trauma during apical cochleostomy. Understanding both distance relationships and expected boundaries of the apex could help to inform future surgical approaches.

Critical Steps and Common Mistakes during Temporal Bone Dissection: A Survey among Residents and a Step-by-Step Guide Analysis

BACKGROUND

Given that the temporal bone is one of the most complex regions of the human body, cadaveric dissection of this anatomical area represents the first necessary step for the learning and training of the young oto-surgeon in order to perform middle ear surgery, which includes the management of inflammatory pathology, hearing rehabilitation, and also cognitive decline prevention surgery. The primary objective of this study was to identify common mistakes and critical passages during the initial steps of temporal bone dissection, specifically cortical mastoidectomy and posterior tympanotomy.

METHODS

A survey among 100 ENT residents was conducted, gathering insights into the most prevalent errors encountered during their training to uncover the most challenging aspects faced by novice surgeons during these procedures.

RESULTS

The most common mistakes included opening the dura of the middle cranial fossa (MCF), injury of the sigmoid sinus (SS), chorda tympani (CT), and facial nerve (FN) injury while performing the posterior tympanotomy. The most important critical steps to prevent mistakes are related to the absence of wide exposure during cortical mastoidectomy and the consequent impossibility of identifying the landmarks of the facial recess before performing posterior tympanotomy. Injury of these structures was more common in younger surgeons and in the ones who performed less than five temporal bone dissection courses.

CONCLUSIONS

Numerous temporal bone dissections on cadavers are mandatory for ENT residents looking forward to performing middle ear surgery.

Subjective and Objective Taste Change After Cochlear Implantation Systematic Review and Meta-Analysis

INTRODUCTION

There is a paucity of data reporting the rate of chorda tympani nerve injury during cochlear implantation (CI) surgery. To better provide clarity to patients and surgeons regarding the risk of taste change, we performed a systematic review and meta-analysis of prospective studies examining taste change after CI.

DATA SOURCES

PubMed, Embase, and Cochrane Library databases were queried.

METHODS

Databases were queried according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Search terms included "(chorda tympani OR gustatory OR taste OR chemosensory OR dysgeusia OR nervus intermedius) AND (cochlea OR cochlear implant OR cochlear implantation)." Prospective studies were included and further divided into "objective" and "subjective" assessments of taste dysfunction. A systematic review was performed for all studies. A random-effects model was used to compare studies with similar methods and patient demographics.

RESULTS

The initial database query yielded 2,437 articles, which were screened according to inclusion and exclusion criteria. Nine appropriate studies were identified, including 442 total patients-254 with subjective assessment and 271 with objective assessment of gustation. Seventeen of 144 patients (11.8%) reported short-term taste change (incidence = 0.09 [0.02-0.16], 95% confidence interval with pooled data). Twenty-six of 265 patients (9.8%) reported long-term taste change (incidence = 0.07 [0.01-0.13]). Objective results were heterogenous and therefore not amenable to pooled meta-analysis.

CONCLUSIONS

Taste change from chorda tympani nerve injury is a likely underrecognized complication of CI and may be the most common adverse consequence of CI surgery. Surgeons should counsel prospective patients on this potential complication and that the risk of taste change may persist longer than the immediate postoperative period.

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.

Enhancement in the Round Window Niche: A Potential Pitfall in High-Resolution MR Imaging of the Internal Auditory Canal

BACKGROUND AND PURPOSE

There is limited discussion in current literature about the normal imaging appearance of the round window. The purpose of this study was to assess the prevalence and imaging characteristics of gadolinium enhancement in the round window niche on MR imaging to the internal auditory canal.

MATERIALS AND METHODS

The presence or absence and laterality of enhancement in the round window niche on MR imaging was retrospectively reviewed in 95 patients from 1 institution. All studies included high-resolution (≤0.5-mm section thickness) pre- and postgadolinium 3D FSE T1 with fat-saturation and postgadolinium 3D FLAIR image sequences. T1 and T2 acquisitions were viewed as coregistered overlays to confirm that enhancement was lateral to the round window membrane within the round window niche. CT was reviewed when available to assess the presence and laterality of soft tissue in the round window niche.

RESULTS

Ninety-five patients with internal auditory canal MRIs were included. Enhancement was present in the round window of 15 of 95 patients (15.8%). Of the 27 patients who underwent CT, 4 (14.8%) had concordant soft tissue on CT and MR imaging enhancement in the round window niche. One patient had MR imaging enhancement within the round window niche without a corresponding abnormality on CT. The absence of soft tissue on CT and the corresponding lack of MR imaging enhancement were present in 22 (81.5%) patients.

CONCLUSIONS

Enhancement can be visualized within the round window niche on MR imaging as an incidental finding. This enhancement probably represents postinflammatory granulation tissue and does not require further intervention. However, the potential for this enhancement to be misdiagnosed as a pathologic process can be a pitfall in MR imaging.

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.

Validation of the radiological detection of the chorda-facial angle: impact on the round window accessibility during pediatric cochlear implantation

OBJECTIVES

The facial recess, an essential landmark for the posterior tympanotomy approach, is limited by the facial nerve and the chorda tympani, with a complicated relationship. This study tried to find the most appropriate radiological method to evaluate the chorda-facial angle (CFA). We also checked the effect of this angle on the round window accessibility during cochlear implantation.

METHODS

It was a retrospective study that included cochlear implant surgeries of 237 pediatric patients, from September 2016 to April 2021. Two physicians evaluated the CFA in the para-sagittal cut of the preoperative HRCT. The round window accessibility was assessed in the unedited surgery videos.

RESULTS

The CFA ranged from 21° to 35° with a mean of 27.14 ± 3.5°. It was detected in all cases with a high agreement between the two CT reviewers' measurements. The CFA differed significantly between the accessible group and the group with difficult accessibility (p value < 0.001). Spearman's correlation coefficient revealed a strong correlation between the CFA and the intraoperative round accessibility. 25.5° was the best cutoff point; below this angle, difficult accessibility into the RW was expected, with high sensitivity, specificity, and accuracy CONCLUSIONS: Our study on a relatively large number of cases provided a precise, valid, reliable, and applicable method to evaluate the CFA in the HRCT scan. We found a significant-close relation between the CFA and the round window accessibility; the difficulty increased with a need for posterior tympanotomy modification when the angle decreased.

KEY POINTS

• Radiological detection of the chorda-facial angle was always problematic, without a previous straightforward method in the literature. • We used the para-sagittal cut of the high-resolution CT scans to evaluate the CFA. This cut was beneficial to seeing the chorda tympani nerve in every examined case. There was a high agreement between the two CT reviewers' measurements. • Preoperative evaluation of the CFA in the HRCT accurately predicted the round window accessibility. Patients with CFA less than 25.5^° were expected to have difficult accessibility into the round window during cochlear implantation.

Surgical considerations during cochlear implantation: the utility of temporal bone computed tomography

OBJECTIVE

This paper describes the construction of portals for electrode placement during cochlear implantation and emphasises the utility of pre-operative temporal bone three-dimensional computed tomography.

METHODS

Temporal bone three-dimensional computed tomography was used to plan portal creation for electrode insertion.

RESULTS

Pre-operative temporal bone three-dimensional computed tomography can be used to determine the orientation of temporal bone structures, which is important for mastoidectomy, posterior tympanotomy and cochleostomy, and when using the round window approach.

CONCLUSION

It is essential to create appropriate portals (from the mastoid cortex to the cochlea) in a step-by-step manner, to ensure the safe insertion of electrodes into the scala tympani. Pre-operative three-dimensional temporal bone computed tomography is invaluable in this respect.

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.

The Anatomy and Anatomical Variations of the Round Window Prechamber and Their Implications on Cochlear Implantation: An Anatomical, Imaging, and Surgical Study

Introduction  Over the last decades, there has been a tremendous increase in the number of cochlear implant recipients and, consequently, there is a recent increase of interest in the proper understanding of the anatomy of the round window (RW), which is the most important anatomical land mark during cochlear implant surgery.

Objectives  The present study was undertaken to assess the detailed surgical and radiological anatomy of the RW prechamber; its shape, directions, measurements, common anatomic variations, and its relationships with different surrounding structures as related to cochlear implantation.

Methods  A total of 20 cadaveric specimens of human temporal bone were microscopically dissected for the anatomical assessment of the measurements of the RW and its relation to surrounding structures in the tympanum. A total of 20 patients were subjected to cochlear implantation, and a radiological and surgical assessment of the anatomy of their RW prechambers was performed.

Results  The distances between the RW and the facial canal (FC), the jugular fossa (JF), the carotid canal (CC), and the oval window (OW) were measured. Among the cases subjected to cochlear implantation, the infracochlear tunnel was studied radiologically; the lengths of the anterior and posterior pillars were assessed, and the relation with the direction at which the RW faces was statistically analyzed.

Conclusions  Proper understanding of the topographic anatomy of the RW, including its direction of opening and the distances from different adjacent structures in the tympanum, is essential for a successful cochlear implantation surgery, since it can help decision-making before the surgery and is useful to avoid many complications, such as misplaced electrode and iatrogenic injury to the surrounding structures.

Bhopal Technique of Cochlear Implantation: A Surgical Review of 50 Cases

Cochlear Implant is the new age treatment for profound deafness especially in children who are unable to hear since birth. This is a life changing technology where in a surgically implanted device can stimulate the auditory nerve through electrical currents enabling the generation of auditory potential. Various surgical techniques have been described in literature but debate exists over Posterior Tympanotomy and Trans-canal "Veria" technique. We are presenting our experience of 50 cases with modified trans-canal technique "The Bhopal Technique" which combines the best of both. 50 patients with bilateral profound deafness in age group 1-5 years were included in this observational study. These children underwent cochlear implantation by Bhopal Technique. The data was categorised into age, gender, certain surgical parameters like time taken; exposure and complications. In present study. The average time taken for surgery was 77.6 min, with electrode insertion in first attempt in about 43 cases. Round Window exposure was adequate in 37 cases while scala tympani was entered in 49 cases. Average time taken for cochleostomy was 44.6 s. Most common complication was wound hyperemia followed by Perilymph Gusher. Explantation was seen in 1 case. Minor complications included Vertigo and Tinnitus. There was one tympanic membrane perforation at 3 months follow up and response to AVT was excellent in 12 children at 6 month follow up. Bhopal technique is emerging as a promising technique for upcoming cochlear implant surgeons due to its low complication rate, better exposure of surgical landmarks and comparable outcomes to Veria and Posterior tympanotomy techniques.

Cochlear Implant Surgery: Endomeatal Approach versus Posterior Tympanotomy

The aim of the present study was to compare the posterior tympanotomy (PT) technique to the endomeatal approach. The endomeatal approach (EMA) for Cochlear Implant (CI) surgery was performed on 98 patients with procident lateral sinus or a small mastoid cavity, on 103 ears (Group A). Conventional mastoidectomy and PT was performed on the other 104 patients, on 107 ears (Group B). Data on all patients were then collected for the following: intra- and post-operative complications, Tinnitus Handicap Inventory (THI), Vertigo Symptom Scale (VSS), duration of surgery, and postoperative discomfort. The difference in the total number of major and minor complications between the case group and the control group was not statistically significant. There was a statistically significant difference in discomfort between the two groups using the Visual Analogue Scale (VAS), both immediately postsurgery (p = 0.02) and after one month (p = 0.04). The mean duration of surgery was 102 ± 29 min for EMA and 118 ± 15 min for the PT technique (p = 0.008). EMA is a faster technique resulting in reduced postoperative patient discomfort in comparison to the PT method. The experience of the surgeon as well as the correct choice of surgical technique are fundamental to successful outcomes for cochlear implant surgery.

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.

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.

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.

Population Statistics Approach for Safety Assessment in Robotic Cochlear Implantation

HYPOTHESIS

Descriptive statistics with respect to patient anatomy and image guidance accuracy can be used to assess the effectiveness of any system for minimally invasive cochlear implantation, on both an individual patient and wider population level.

BACKGROUND

Minimally invasive cochlear implantation involves the drilling of a tunnel from the surface of the mastoid to cochlea, with the trajectory passing through the facial recess. The facial recess anatomy constrains the drilling path and places prohibitive accuracy requirements on the used system. Existing single thresholds are insufficient for assessing the effectiveness of these systems.

METHODS

A statistical model of the anatomical situation encountered during minimally invasive drilling of the mastoid for cochlear implantation was developed. A literature review was performed to determine the statistical distribution of facial recess width; these values were confirmed through facial recess measurements on computed tomography (CT) data. Based on the accuracy of a robotic system developed by the authors, the effect of variation of system accuracy, precision, and tunnel diameter examined with respect to the potential treatable portion of the population.

RESULTS

A facial recess diameter of 2.54 ± 0.51 mm (n = 74) was determined from a review of existing literature; subsequent measurements on CT data revealed a facial recess diameter of 2.54 ± 0.5 mm (n = 23). The developed model demonstrated the effects of varying accuracy on the treatable portion of the population.

CONCLUSIONS

The presented model allows the assessment of the applicability of a system on a wider population scale beyond examining only the system's ability to reach an arbitrary threshold accuracy.

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.

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.

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.

The feasibility of endoscopic transcanal approach for insertion of various cochlear electrodes: a pilot study

To determine the feasibility of inserting various types of electrode arrays using an endoscopic transcanal approach into the cochlea via the round window membrane (RWM). All the procedures were performed by the first author and started with a cortical mastoidectomy. A six o'clock vertical incision was made in the meatal skin, and a posterior tympano-meatal flap was elevated transmeatally to expose the middle ear cavity using a rigid 0° endoscope (diameter 3 mm, length 14 cm). The chorda tympani nerve (CTN) and body of the incus were exposed. The RWM was incised, and the electrodes were passed through the tunnel from the mastoid to the epitympanum, medial to the CTN and lateral to the incus into the round window (RW) in seven procedures. In the other six cases, an open groove had been drilled, starting superiorly and laterally to the CTN and ending in the mastoid region. After electrodes insertion, the groove was filled with bone dust and covered with a large piece of fascia prior to repositioning of the tympano-meatal flap. Complete electrode insertion (7 Nucleus Contour Advance, 5 Concerto and 1 HiRes90K) via the RW was achieved in all 13 cases. Endoscopic CI was more feasible for insertion of concerto electrode followed by HiRes90K and Nucleus. An assistance of another surgeon was required for removal of stylet in the "off-the-stylet technique" utilized for implantation of nucleus electrode. Endoscopic transcanal implantation of different cochlear electrodes through the RW is feasible in both children and adults and can be used as first surgical option or as a complementary to the traditional posterior tympanotomy approach.

The round window: is it the "cochleostomy" of choice? Experience in 130 consecutive cochlear implants

OBJECTIVE

To demonstrate that the round window insertion (RWI) for cochlear implantation with multichannel electrodes is a reliable, safe, and effective technique.

STUDY DESIGN

Retrospective case review.

SETTING

Academic tertiary referral center.

PATIENTS

One hundred thirty consecutive cochlear implants (72 female and 58 male subjects) performed from August 2009 to August 2011. Devices included 83 Cochlear, 40 Med El, and 7 Advanced Bionics (AB) cochlear implants.

INTERVENTION

Subsequent to a full audiometric assessment, patients underwent a mastoidectomy with facial recess approach whereby the primary surgical objective was to perform a RWI. When the surgeon was unable to access the round window safely, a cochleostomy was performed anterior and inferior to the round window. Postoperative performance was measured with Hearing in Noise Test, the Consonant-Nucleus-Consonant test, and/or the Arizona Biomedical Sentences test.

MAIN OUTCOME MEASURES

Surgical feasibility of reliably performing a RWI, reason for cochleostomy, postoperative complications, and audiometric performance.

RESULTS

In 111 (85.4%) of 130 procedures, a RWI was performed; in 19 (14.6%), a cochleostomy was readily performed by the same approach. Reasons for creating a cochleostomy included facial nerve and jugular bulb location. There were no major postoperative complications in either group and 13 total minor complications. There was no statistically significant difference in postoperative complications or in audiometric performance between the 2 groups.

CONCLUSION

The RWI may offer several advantages over a cochleostomy, and it seems to be a reliable, safe, and effective technique for cochlear implantation with today's cochlear implant electrodes. Further studies would be necessary to verify these findings for broad application to the cochlear implant patient population.

Surgical and radiologic anatomy of a cochleostomy produced via posterior tympanotomy for cochlear implantation based on three-dimensional reconstructed temporal bone CT images

PURPOSE

In this study, we evaluated the surgical and radiologic anatomy of a cochleostomy produced via posterior tympanotomy for cochlear implantation (CI).

MATERIALS AND METHODS

Twenty computed tomography (CT) images of the temporal bone from patients aged between 20 and 60 years were selected. The inclusion criterion was a radiologically normal temporal bone CT scan. Three-dimensional (3D) reconstructed images were obtained using high-resolution axial temporal bone CT scans. Eight points were used to evaluate the surgical anatomy of the posterior tympanotomy and cochleostomy. The length of lines between the points and the angles between the lines were measured.

RESULTS

The mean length of line AB (superior-inferior length of the posterior tympanotomy for CI) was 6.48 ± 0.26 mm, while line AC (width of the chorda tympani and facial nerves) was 3.60 ± 0.2 mm. The mean angle of ABC (angle at which the chorda tympani nerve branched from the facial nerve) was 18.40° ± 1.05°. The mean length of line AD (distance from the facial ridge to the point of cochleostomy) was 9.58 ± 0.47 mm.

CONCLUSIONS

3D imaging of the facial recess and round window can be used to identify the facial recess before surgery. This may help to avoid injury to the chorda tympani nerve during posterior tympanotomy, and make it easier to insert the electrode array during CI by creating a large enough posterior tympanotomy to avoid injury to the facial nerve, which can cause immediate or delayed facial palsy.

Human cochlea: anatomical characteristics and their relevance for cochlear implantation

This is a review of the anatomical characteristics of human cochlea and the importance of variations in this anatomy to the process of cochlear implantation (CI). Studies of the human cochlea are essential to better comprehend the physiology and pathology of man's hearing. The human cochlea is difficult to explore due to its vulnerability and bordering capsule. Inner ear tissue undergoes quick autolytic changes making investigations of autopsy material difficult, even though excellent results have been presented over time. Important issues today are novel inner ear therapies including CI and new approaches for inner ear pharmacological treatments. Inner ear surgery is now a reality, and technical advancements in the design of electrode arrays and surgical approaches allow preservation of remaining structure/function in most cases. Surgeons should aim to conserve cochlear structures for future potential stem cell and gene therapies. Renewal interest of round window approaches necessitates further acquaintance of this complex anatomy and its variations. Rough cochleostomy drilling at the intricate "hook" region can generate intracochlear bone-dust-inducing fibrosis and new bone formation, which could negatively influence auditory nerve responses at a later time point. Here, we present macro- and microanatomic investigations of the human cochlea viewing the extensive anatomic variations that influence electrode insertion. In addition, electron microscopic (TEM and SEM) and immunohistochemical results, based on specimens removed at surgeries for life-threatening petroclival meningioma and some well-preserved postmortal tissues, are displayed. These give us new information about structure as well as protein and molecular expression in man. Our aim was not to formulate a complete description of the complex human anatomy but to focus on aspects clinically relevant for electric stimulation, predominantly, the sensory targets, and how surgical atraumaticity best could be reached.

Surgical planning and evaluation of implanting a penetrating cochlear nerve implant in human temporal bones using microcomputed tomography

OBJECTIVE

To develop a transmastoid-posterior tympanotomy approach for the implantation of a penetrating auditory prosthesis in the most distal portion of the cochlear nerve.

BACKGROUND

Animal studies suggest that penetrating cochlear nerve implants may overcome limitations of current cochlear implant systems. One step toward human implantation is the development of a suitable surgical approach.

METHODS

In computer-rendered 3-dimensional (3-D) models (based on micro-CT scans of 10 human temporal bones), we simulated trajectories through the most basal part of the cochlea that gave access to the most distal portion of the cochlear nerve with minimal damage to intracochlear structures. We determined their vectors with respect to the mid-modiolar axis and posterior round window edge and assessed if they intersected the chorda tympani nerve.

RESULTS

The typical vector obtained with these 3-D models ran in an anterosuperior direction, through the inferior part of the facial recess and anterior round window edge. In 7 of 10 temporal bones, this trajectory intersected the chorda tympani nerve. Based on the vectors, dummy probes were implanted in 3 of 10 temporal bones, and the need for chorda tympani removal was confirmed in accordance with the 3-D models. Postoperative micro-CT scans revealed that all probes were successfully implanted in the cochlear nerve, whereas the osseous spiral lamina and basilar membrane were preserved.

CONCLUSION

The vector for drilling and implantation found in this study can be used as a guideline for real-life surgery and, therefore, is another step toward the clinical implementation of cochlear nerve implants.

Cochlear implant challenges encountered in tuberculous otitis media

Tuberculous otitis media (TOM) is rare in ENT department, and is frequently misdiagnosed as otitis media. Thus early systemic treatment is very important for TOM. We reported a case report with TOM to highlight development of the disease and difficulties in clinical treatment in late stage of TOM. Implantation of ossified and eroded cochlea poses many unique challenges to both the surgeon and programming team. With thorough preparation and complete knowledge about characters of specific issues, implantation would be performed successfully, and patients with ossified cochlear could benefit from cochlear implantation.

Preliminary results in cochlear implant surgery without antromastoidectomy and with atraumatic electrode insertion: the endomeatal approach

A surgical approach using the external auditory canal and the round window as a natural access pathway for cochlear implant positioning, the endomeatal approach, is described. This approach avoids performing an antromastoidectomy, the subsequent posterior tympanotomy and the promontorial cochleostomy. The endomeatal approach also allows an optimal insertion plane for electrode array atraumatic insertion through the round window.The technique was developed and practiced in 35 fresh temporal bones and then it was applied in ten patients. This surgery has an endomeatal first stage, which begins with a stapedectomy-like tympanomeatal flap. This flap allows an easy access to scala tympani via round window niche. The internal part of a groove is drilled on the posterior wall of the EAC. The groove is parallel to the EAC axis and starts in its inner border. Once the endomeatal stage is completed, a standard retroauricular approach is performed, in order to make the receptor-stimulator well and to complete the groove externally, until it connects the middle ear with the external mastoid surface. A flat second well is drilled in front of the first one to lodge the remaining electrode lead. In small children this well is deepened. The electrode array is introduced in the scala tympani through the RW and located into the groove. The electrode is covered and fixed inside the groove with bone paté. The extra length of the electrode lead is located in the second well and the receptor-stimulator is fixed in its well. The ground electrode is placed under the periosteum, the retroauricular incision is sutured, the tympanomeatal flap is restored and a dressing is placed into the EAC. Surgical time was significantly shorter than in standard approach. There were neither surgical nor healing complications. Electrode insertion was easy and complete and functional results were adequate. The goal of this approach is to avoid antromastoidectomy and posterior tympanotomy, which are replaced by the EAC groove. It is faster and safer, eliminating the risk of facial nerve injury. It also allows a better access to the round window, with a less traumatic electrode insertion, suitable for "soft surgery" performing. It may advantageously replace the classical transmastoideal approach.

Role of 3D CT in the Evaluation of the Temporal Bone

In recent years, three-dimensional (3D) multiplanar reformatted images from conventional cross-sectional computed tomographic (CT) data have been increasingly used to better demonstrate the anatomy and pathologic conditions of various organ systems. Three-dimensional volume-rendered (VR) CT images can aid in understanding the temporal bone, a region of complex anatomy containing multiple small structures within a relatively compact area, which makes evaluation of this region difficult. These images can be rotated in space and dissected in any plane, allowing assessment of the morphologic features of individual structures, including the small ossicles of the middle ear and the intricate components of the inner ear. The use of submillimeter two-dimensional reconstruction from CT data in addition to 3D reformation allows depiction of microanatomic structures such as the osseous spiral lamina and hamulus. Furthermore, 3D VR CT images can be used to evaluate various conditions of the temporal bone, including congenital malformations, vascular anomalies, inflammatory or neoplastic conditions, and trauma. The additional information provided by 3D reformatted images allows a better understanding of temporal bone anatomy and improves the ability to evaluate related disease, thereby helping to optimize surgical planning.

Development and surgical anatomy of the round window niche

The round window niche is a bony pouch of the tympanic cavity and clinically frequently explored, therefore its topography has fundamental impact on microsurgery. A total of 783 macerated and formalin-fixed temporal bones were used to study the normal anatomy of the round window and its development. The ossification of the niche starts in the 16th fetal week and is complete at birth. A process of the otic capsule, called the cartilage bar, forms the inferior wall of the round window niche. The anterior and superior walls of the niche form by intramembranous ossification, whereas the posterior and inferior walls predominantly form by enchondral ossification. The uneven growth of different walls of the round window niche can alter the shape of the entrance, which results in eight different types of niches: extremely narrow, descending tegmen, anterior septum, bony membrane, open fundus, exostosis, jugular dome and trabeculae.

Cochlear orientation and dimensions of the facial recess in cochlear implantation

OBJECTIVE

To study the dimensions of the facial recess and the spatial relationship between the facial recess and the cochlea, using CT scanning in cochlear implantees.

METHOD

In 29 cochlear implantees, preoperative CT scans of the temporal bone were compared with findings done at surgery. The dimensions of the facial recess and the relationship between the facial recess and the cochlea were both measured on a viewing station and classified on printed films by 3 blinded and independent reviewers.

RESULTS

No significant relations could be found between either intuitive classification of facial recess width or electrode array insertion feasibility and the measurements with the viewing station. The 3 reviewers had large interobserver variability. In 5 cases, neither intuitive review of the CT scans nor viewing station measurements could predict any of the problems encountered during surgery.

CONCLUSION

Our findings show that intuitive review was not reliable in classifying facial recess width. Viewing station measurements, in classifying the spatial relation between the facial recess and the cochlear basal turn, need a more detailed review in terms of the relationship with the operation direction and the orientation of the basal turn of the cochlea. Advanced imaging techniques, specifically multislice CT, might improve the diagnostic capabilities.