Cochlear Implantation With a Novel Long Straight Electrode: the Insertion Results Evaluated by Imaging and Histology in Human Temporal Bones

Predicting Matrix Test Effectiveness for Evaluating Auditory Performance in Noise Using Pure-Tone Audiometry and Speech Recognition in Quiet in Cochlear Implant Recipients

INTRODUCTION

Auditory performance in noise of cochlear implant recipients can be assessed with the adaptive Matrix test (MT); however, when the speech-to-noise ratio (SNR) exceeds 15 dB, the background noise has any negative impact on the speech recognition. Here, we aim to evaluate the predictive power of aided pure-tone audiometry and speech recognition in quiet and establish cut-off values for both tests that indicate whether auditory performance in noise can be assessed using the Matrix sentence test in a diffuse noise environment.

METHODS

Here, we assessed the power of pure-tone audiometry and speech recognition in quiet to predict the response to the MT. Ninety-eight cochlear implant recipients were assessed using different sound processors from Advanced Bionics (n = 56) and CochlearTM (n = 42). Auditory tests were performed at least 1 year after cochlear implantation or upgrading the sound processor to ensure the best benefit of the implant. Auditory assessment of the implanted ear in free-field conditions included: pure-tone average (PTA), speech discrimination score (SDS) in quiet at 65 dB, and speech recognition threshold (SRT) in noise that is the SNR at which the patient can correctly recognize 50% of the words using the MT in a diffuse sound field.

RESULTS

The SRT in noise was determined in 60 patients (61%) and undetermined in 38 (39%) using the MT. When cut-off values for PTA <36 dB and SDS >41% were used separately, they were able to predict a positive response to the MT in 83% of recipients; using both cut-off values together, the predictive value reached 92%.

DISCUSSION

As the pure-tone audiometry is standardized universally and the speech recognition in quiet could vary depending on the language used; we propose that the MT should be performed in recipients with PTA <36 dB, and in recipients with PTA >36 dB, a list of Matrix sentences at a fixed SNR should be presented to determine the percentage of words understood. This approach should enable clinicians to obtain information about auditory performance in noise whenever possible.

Automatic electrode scalar location assessment after cochlear implantation using a novel imaging software

As of today, image-based assessment of cochlear implant electrode array location is not part of the clinical routine. Low resolution and contrast of computer tomography (CT) imaging, as well as electrode array artefacts, prevent visibility of intracochlear structures and result in low accuracy in determining location of the electrode array. Further, trauma assessment based on clinical-CT images requires a uniform image-based trauma scaling. Goal of this study was to evaluate the accuracy of a novel imaging software to detect electrode scalar location. Six cadaveric temporal bones were implanted with Advanced Bionics SlimJ and Mid-Scala electrode arrays. Clinical-CT scans were taken pre- and postoperatively. In addition, micro-CTs were taken post-operatively for validation. The electrode scalar location rating done by the software was compared to the rating of two experienced otosurgeons and the micro-CT images. A 3-step electrode scalar location grading scale (0 = electrode in scala tympani, 1 = interaction of electrode with basilar membrane/osseous spiral lamina, 2 = translocation of electrode into scala vestibuli) was introduced for the assessment. The software showed a high sensitivity of 100% and a specificity of 98.7% for rating the electrode location. The correlation between rating methods was strong (kappa > 0.890). The software gives a fast and reliable method of evaluating electrode scalar location for cone beam CT scans. The introduced electrode location grading scale was adapted for assessing clinical CT images.

Trauma After Cochlear Implantation: The Accuracy of Micro-Computed Tomography and Cone-Beam Fusion Computed Tomography Compared With Histology in Human Temporal Bones

HYPOTHESIS

Micro-computed tomography (micro-CT) and cone-beam computed tomography (CBCT), in conjunction with the image fusion technique, may provide similar results for trauma assessment after cochlear implantation, with respect to the trauma evaluation in preclinical cochlear implant (CI) studies, as the histology.

BACKGROUND

Before clinical use, novel cochlear implant (CI) designs are tested in temporal bone (TB) studies for usability and risk evaluation. The criterion standard for evaluating intracochlear insertion trauma and electrode location has historically been with histological samples. Progress of modern imaging technology has created alternatives to classic histology. This study compares the micro-CT and CBCT fusion images between histological samples in a preclinical CI study.

METHODS

Fourteen freshly frozen TBs were inserted with a lateral wall research CI electrode. All TBs were scanned with CBCT preoperatively and postoperatively. After insertion, the TBs were prepared for micro-CT and histology. Twelve TBs underwent first a micro-CT and then the histological process. The CBCTs were used for image fusion, and all three different methods were used for intracochlear trauma evaluation. The results were compared between methods.

RESULTS

There were 4 of 14 translocations detected with the fusion image method and 3 of 12 with the micro-CT and histology. When compared, the trauma grades converged and were not statistically significant.

CONCLUSION

The trauma grading based on micro-CT is comparable to the histology. The image fusion technique based on CBCT is less accurate because it relies on an empirical assumption of the basal membrane localization, but it is clinically applicable.

The effect of the surgical approach and cochlear implant electrode on the structural integrity of the cochlea in human temporal bones

Cochlear implants (CI) restore hearing of severely hearing-impaired patients. Although this auditory prosthesis is widely considered to be very successful, structural cochlear trauma during cochlear implantation is an important problem, reductions of which could help to improve hearing outcomes and to broaden selection criteria. The surgical approach in cochlear implantation, i.e. round window (RW) or cochleostomy (CO), and type of electrode-array, perimodiolar (PM) or lateral wall (LW), are variables that might influence the probability of severe trauma. We investigated the effect of these two variables on scalar translocation (STL), a specific type of severe trauma. Thirty-two fresh frozen human cadaveric ears were evenly distributed over four groups receiving either RW or CO approach, and either LW or PM array. Conventional radiological multiplanar reconstruction (MPR) was compared with a reconstruction method that uncoils the spiral shape of the cochlea (UCR). Histological analysis showed that RW with PM array had STL rate of 87% (7/8), CO approach with LW array 75% (6/8), RW approach with LW array 50% (4/8) and CO approach with PM array 29% (2/7). STL assessment using UCR showed a higher inter-observer and histological agreement (91 and 94% respectively), than that using MPR (69 and 74% respectively). In particular, LW array positions were difficult to assess with MPR. In conclusion, the interaction between surgical approach and type of array should be preoperatively considered in cochlear implant surgery. UCR technique is advised for radiological assessment of CI positions, and in general it might be useful for pathologies involving the inner ear or other complex shaped bony tubular structures.

Intracochlear New Fibro-Ossification and Neuronal Degeneration Following Cochlear Implant Electrode Translocation: Long-Term Histopathological Findings in Humans

OBJECTIVE

We aim to assess the histopathology of human temporal bones (TBs) with evidence of cochlear implantation (CI) electrode scalar translocation.

STUDY DESIGN

Otopathology study.

SETTING

Otopathology laboratory.

PATIENTS

TBs from patients who had a history of CI and histopathological evidence of interscalar translocation. Specimens with electrode placed entirely within the ST served as controls.

INTERVENTION

Histopathological assessment of human TBs.

MAIN OUTCOME MEASURES

TBs from each patient were harvested postmortem and histologically analyzed for intracochlear changes in the context of CI electrode translocation and compared to controls. Intracochlear new fibro-ossification, and spiral ganglion neuron (SGN) counts were assessed. Postoperative word recognition scores (WRS) were also compared.

RESULTS

Nineteen human TBs with electrode translocation and eight controls were identified. The most common site of translocation was the ascending limb of the basal turn (n = 14 TBs). The average angle of insertion at the point of translocation was 159° ± 79°. Eighteen translocated cases presented moderate fibroosseous changes in the basal region of the cochlea, extending to the translocation point and/or throughout the electrode track in 42%. Lower SGN counts were more pronounced in translocated cases compared to controls, with a significant difference for segment II (p = 0.019). Although final postoperative hearing outcomes were similar between groups, translocated cases had slower rate of improvement in WRS (p = 0.021).

CONCLUSIONS

Cochlear implant electrode translocation was associated with greater fibroosseous formation and lower SGN population. Our findings suggest that scalar translocations may slow the rate of improvement in WRS overtime as compared to atraumatic electrode insertions.Level of evidence: IV.

Cochlear implantation: Exploring the effects of 3D stereovision in a digital microscope for virtual reality simulation training - A randomized controlled trial

In cochlear implantation (CI), excellent surgical technique is critical for hearing outcomes. Recent advances in temporal bone Virtual Reality (VR) training allow for specific training of CI and through introduction of new digital microscopes with ultra-high-fidelity (UHF) graphics. This study aims to investigate whether UHF increases performance in VR simulation training of CI electrode insertion compared with conventional, screen-based VR (cVR).

METHODS

Twenty-four medical students completed a randomized, controlled trial of an educational intervention. They performed a total of eight CI electrode insertions each in blocks of four using either UHF-VR or cVR, in randomized order. CI electrode insertion performances were rated by two blinded expert raters using a structured assessment tool supported by validity evidence.

RESULTS

Performance scores in cVR were higher than in the UHF-VR simulation although this was not significant (19.8 points, 95% CI [19.3-20.3] vs. 18.8 points, 95% CI [18.2-19.4]; P = 0.09). The decisive factor for performance was participants' ability to achieve stereovision (mean difference = 1.1 points, 95% CI [0.15-2.08], P = 0.02).

DISCUSSION

No additional benefit was found from UHF-VR over cVR training of CI electrode insertion for novices. Consequently, standard cVR simulation should be used for novices' basic skills acquisition in CI surgery. Future studies should instead explore the effects of other improvements in CI surgery training and if the lacking benefit of UHF-VR also applies for more experienced learners.

CONCLUSION

The increased graphical perception and the superior lifelikeness of UHF-VR does not improve early skills acquisition of CI insertion for novices.

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

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

Assessing competence in cochlear implant surgery using the newly developed Cochlear Implant Surgery Assessment Tool

PURPOSE

To develop and gather validity evidence for a novel tool for assessment of cochlear implant (CI) surgery, including virtual reality CI surgery training.

METHODS

Prospective study gathering validity evidence according to Messick's framework. Four experts developed the CI Surgery Assessment Tool (CISAT). A total of 35 true novices (medical students), trained novices (residents) and CI surgeons performed two CI-procedures each in the Visible Ear Simulator, which were rated by three blinded experts. Classical test theory and generalizability theory were used for reliability analysis.

RESULTS

The CISAT significantly discriminated between the three groups (p < 0.001). The generalizability coefficient was 0.76 and most of the score variance (53.3%) was attributable to the participant and only 6.8% to the raters. When exploring a standard setting for CI surgery, the contrasting groups method suggested a pass/fail score of 36.0 points (out of 55), but since the trained novices performed above this, we propose using the mean CI surgeon performance score (45.3 points).

CONCLUSION

Validity evidence for simulation-based assessment of CI performance supports the CISAT. Together with the standard setting, the CISAT might be used to monitor progress in competency-based training of CI surgery and to determine when the trainee can advance to further training.

Auditory performance of post-lingually deafened adult cochlear implant recipients using electrode deactivation based on postoperative cone beam CT images

PURPOSE

The use of image processing techniques to estimate the position of intra-cochlear electrodes has enabled the creation of personalized maps to meet the individual stimulation needs of cochlear implant (CI) recipients. The aim of this study was to evaluate a novel technique of electrode deactivation based on postoperative cone beam computed tomography (CBCT) images in post-lingually deafened adult CI recipients.

METHODS

Based on postoperative CBCT images, the positioning of the electrodes was estimated in relation to the modiolus in 14 ears of 13 post-lingually deafened adult CI recipients. The electrodes sub-optimally positioned or involved in kinking and tip fold-over were deactivated. Speech perception scores in silence and in noise were obtained from subjects using the standard map and were followed up 4 weeks after image-based electrode deactivation reprogramming technique (IBEDRT). The participants selected their preferred map after 4 weeks of IBEDRT use.

RESULTS

There were statistically significant improvements in the speech recognition tests in silence and noise when comparing IBEDRT performance to the standard map. All participants elected the IBEDRT as their new preferred map.

CONCLUSIONS

IBEDRT is a promising technique for fitting CI recipients and minimizing channel interaction increased by the positioning of the electrodes sub-optimally placed, thereby improving their auditory performance. We propose a novel electrode deactivation technique based on postoperative CBCT imaging, with a limited number of deactivated electrodes and a low-dosing scanning which could be applied for clinical routine.

A New Application of CBCT Image Fusion in Temporal Bone Studies

OBJECTIVES

Temporal bone (TB) studies are essential during the development of new arrays. Postoperative cochlear histology is still regarded as golden standard for the assessment of electrode localization and trauma though it is time consuming, expensive and technically very demanding. The aim of this study is to investigate whether pre-operative evacuation of perilymph improve the assessment of electrode localization and insertion trauma in TBs applying fusion imaging. The results were compared to a prior validated image fusion technique based on the quantification of the electrode placement.

MATERIALS AND METHODS

12 prototype electrodes were implanted in fresh frozen TBs. The perilymph was evacuated from the scale prior to pre-operative cone-beam computer tomography (CBCT). The TB were then immersed in Ringer solution to rehydrated both scalae. After electrode insertion post-operative CBCT were obtained. 3D fusions of the pre- and postoperative registration were reconstructed. The electrode localization with respect to the basilar membrane was visually assessed.

RESULTS

The visualization of the BM on the pre-operative scans was achieved beyond the second turn in all TBs. The visual assessment was found to be as accurate as the previously validated fusion technique. There was no statistically significant difference between the methods (p=0.564). The image reconstructions and evaluations, however, were faster to perform and the insertion results are immediately available.

CONCLUSION

CBCT in combination with pre- and postoperative image fusion is an accurate method for the post-operative assessment of insertion trauma in TBs. This new application facilitates the identification of the BM and allows for a visual assessment of insertion trauma.

The Image Fusion Technique for Cochlear Implant Imaging: A Study of its Application for Different Electrode Arrays

OBJECTIVES

To investigate the benefits of the image fusion technique for precise postoperative assessment of intracochlear placement with six different electrode arrays.

STUDY DESIGN

Consecutive retrospective case study.

SETTINGS

Tertiary referral center.

PATIENTS

Analyses of imaging data of 30 patients implanted with six different electrode arrays.

INTERVENTIONS

Electrode reconstructions obtained from postoperative cone-beam computed tomography (CBCT) were overlaid onto preoperative magnetic resonance imaging (MRI) and/or high-resolution computed tomography (HRCT) registrations to create artefact-free images.

MAIN OUTCOME MEASURES

Each electrode's intracochlear position was analyzed with the image fusion reconstructions and compared with the results obtained by CBCT alone. The electrode location was classified according to its position in relation to the basal membrane at four different insertion angles.

RESULTS

In 40 out of 151 measurements (26.5%), the location grading obtained by CBCT alone changed after the assessment with the image fusion reconstructions. A significant association was found between deep insertions (over 360 degrees) and the effectiveness of image fusion (p = 0.019). The difference between the impact of the fusion technique for the basal turn versus the apical part was highly significant (p = 0.001). There was no significant difference between the effectiveness of the image fusion and the different electrodes.

CONCLUSIONS

By utilizing an image fusion technique, a more accurate assessment of electrode placement could be achieved for all types of electrodes. Image fusion was especially beneficial for insertions beyond 360 degrees.

The Insertion Results of a Mid-scala Electrode Assessed by MRI and CBCT Image Fusion

OBJECTIVES

To investigate the results of clinical surgical insertions with a Mid-scala array (HIFocus Mid-Scala Electrode, HFms).

STUDY DESIGN

Consecutive retrospective case study.

SETTINGS

Tertiary referral center.

PATIENTS

Analyses of imaging data of 26 consecutive patients (31 insertions) implanted with the HFms.

INTERVENTION (S)

The evaluation of insertion trauma evoked by a previously validated image fusion technique. Electrode reconstructions from postoperative cone-beam computed tomography (CBCT) were overlaid onto preoperative magnetic resonance imaging (MRI) scans to create artifact-free images.

MAIN OUTCOME MEASURES

The electrode position was quantified in relation to the basilar membrane. Trauma scaling adopted from Eshraghi was used for evaluating insertion trauma. The results of the visual assessment of the postoperative CBCT were compared to those obtained with the fusion technique.

RESULTS

Three insertions had to be excluded due to incompatibility of the imaging data with the fusion software. We found consistent peri- to mid-modiolar placement of the HFms with a mean insertion depth angle of 376°. According to the medical records, a visual examination of the postoperative CBCT indicated that there had been no scala dislocations but when assessed by the image fusion technique, five scala dislocations (17.8%) were found. Additionally, one tip fold-over was detected in the postoperative CBCT even though this was not evident in any intraoperative measurements.

CONCLUSION

HFms showed atraumatic surgical insertion results with consistent mid-modiolar placement. Image fusion enhances the accuracy of the insertion trauma assessment. Routine postoperative imaging is recommended for identifying tip fold-over as well as for quality control and documentation.

Radiologic measurement of cochlea and hearing preservation rate using slim straight electrode (CI422) and round window approach

Hearing preservation surgery constitutes a considerable branch of cochlear implantation surgery and is being steadily developed and perfected. The aim of the study was to verify if insertion of a cochlear implant electrode according to individually calculated linear insertion depth improves hearing preservation. We evaluated the relations between the size of a cochlea, insertion depth angle, linear insertion depth and hearing preservation rate (HP) according to Hearing Preservation Classification in a retrospective case review of 54 patients implanted with a slim straight electrode Nucleus CI422 in 2008-2011. Group HP was 0.75 at activation, 0.67 at 12 months (for 53 patients) and 0.60 at 24 months. In 53 cases, the mean insertion depth angle was 375° (SD 17°); mean calculated cochlear duct length 35.87 mm (SD 1.95); mean calculated linear insertion depth 23.14 mm (SD 1.68). There was no significantly relevant relation between HP values and angular insertion depth or insertion depth. Preoperative measurements of cochlea and specific parameters such as linear insertion depth have no effect on hearing preservation. Poor hearing preservation in some deep insertion cases cannot be explained entirely by the electrode position.