Further Evidence of the Relationship Between Cochlear Implant Electrode Positioning and Hearing Outcomes

BACKGROUND

Postoperative imaging studies by numerous groups have revealed that final cochlear implant (CI) electrode position impacts audiological outcomes with scalar location consistently shown to be a significant factor. Modiolar proximity has been less extensively studied, and findings regarding the effect of insertion depth have been inconsistent.

METHODS

Using previously developed automated algorithms, we determined CI electrode position in an Institutional Review Board-approved database of 220 CI ears. Generalized linear models (GLM) were used to analyze the relationship between audiological outcomes and factors including age, duration of CI use, device type, and electrode position.

RESULTS

For precurved arrays, GLM revealed that scalar position, modiolar proximity, base insertion depth, and sex were significant factors for Consonant-Nucleus-Consonant (CNC) words (R = 0.43, p < 0.001, n = 92 arrays), while scalar position, modiolar proximity, age, and postlingual onset of deafness were significant for Bamford-Kawal-Bench Sentences in Noise (BKB-SIN) (R = 0.51, p < 0.001, n = 85) scores. Other factors were not significant in the final model after controlling for these variables. For straight arrays, we found the insertion depth, postlingual deafness, and length of CI use to be highly significant (R = 0.47, p < 0.001) factors for CNC words (91 arrays), while for BKB-SIN scores the most significant (R = 0.47, p < 0.001) factors were insertion depth, younger age, and postlingual deafness (89 arrays).

CONCLUSION

Our results confirm the significance of electrode positioning in audiological outcomes. The most significant positional predictors of outcome for precurved arrays were full scala tympani (ST) insertion and the modiolar distance, while for the lateral wall arrays the depth of insertion was the most significant factor.

Intracochlear PLGA based implants for dexamethasone release: Challenges and solutions

The effective treatment of diseases of the inner ear is currently an unmet medical need. Local controlled drug delivery to the cochlea is challenging due to the hidden location, small volume and high sensitivity of this organ. A local intracochlear delivery of drugs would avoid the problems of intratympanic (extracochlear) drug application, but is more invasive. The requirements for such a delivery system include a small size and appropriate flexibility. The delivery device must be rigid enough for surgical handling but also flexible to avoid traumatizing cochlear structures. We developed biodegradable dexamethasone loaded PLGA extrudates for the controlled intracochlear release. In order to achieve the desired flexibility, Polyethylene glycol (PEG) was used as a plasticizer. In addition to the drug release, the extrudates were characterized in vitro by differential scanning calorimetry (DSC) and texture analysis. Simulation of the pharmacokinetics of the inner ear support the expectation that a constant perilymph drug level is obtained after few hours and retained over several weeks. Ex vivo implantation of the extrudates into a guinea pig cochlea indicate that PEG containing extrudates have the desired balance between mechanical strength and flexibility for direct implantation into the cochlea. The location of the implant was visualized by computer tomography. In summary, we postulate that intracochlear administration of drug releasing biodegradable implants is a new and promising approach to achieve local drug delivery to the cochlea for an extended time.

Response Changes During Insertion of a Cochlear Implant Using Extracochlear Electrocochleography

OBJECTIVES

Electrocochleography is increasingly being utilized as an intraoperative monitor of cochlear function during cochlear implantation (CI). Intracochlear recordings from the advancing electrode can be obtained through the device by on-board capabilities. However, such recordings may not be ideal as a monitor because the recording electrode moves in relation to the neural and hair cell generators producing the responses. The purposes of this study were to compare two extracochlear recording locations in terms of signal strength and feasibility as intraoperative monitoring sites and to characterize changes in cochlear physiology during CI insertion.

DESIGN

In 83 human subjects, responses to 90 dB nHL tone bursts were recorded both at the round window (RW) and then at an extracochlear position-either adjacent to the stapes or on the promontory just superior to the RW. Recording from the fixed, extracochlear position continued during insertion of the CI in 63 cases.

RESULTS

Before CI insertion, responses to low-frequency tones at the RW were roughly 6 dB larger than when recording at either extracochlear site, but the two extracochlear sites did not differ from one another. During CI insertion, response losses from the promontory or adjacent to the stapes stayed within 5 dB in ≈61% (38/63) of cases, presumably indicating atraumatic insertions. Among responses which dropped more than 5 dB at any time during CI insertion, 12 subjects showed no response recovery, while in 13, the drop was followed by partial or complete response recovery by the end of CI insertion. In cases with recovery, the drop in response occurred relatively early (<15 mm insertion) compared to those where there was no recovery. Changes in response phase during the insertion occurred in some cases; these may indicate a change in the distributions of generators contributing to the response.

CONCLUSIONS

Monitoring the electrocochleography during CI insertion from an extracochlear site reveals insertions that are potentially atraumatic, show interaction with cochlear structures followed by response recovery, or show interactions such that response losses persist to the end of recording.

Automatic graph-based method for localization of cochlear implant electrode arrays in clinical CT with sub-voxel accuracy

Cochlear implants (CIs) are neural prosthetics that provide a sense of sound to people who experience severe to profound hearing loss. Recent studies have demonstrated a correlation between hearing outcomes and intra-cochlear locations of CI electrodes. Our group has been conducting investigations on this correlation and has been developing an image-guided cochlear implant programming (IGCIP) system to program CI devices to improve hearing outcomes. One crucial step that has not been automated in IGCIP is the localization of CI electrodes in clinical CTs. Existing methods for CI electrode localization do not generalize well on large-scale datasets of clinical CTs implanted with different brands of CI arrays. In this paper, we propose a novel method for localizing different brands of CI electrodes in clinical CTs. We firstly generate the candidate electrode positions at sub-voxel resolution in a whole head CT by thresholding an up-sampled feature image and voxel-thinning the result. Then, we use a graph-based path-finding algorithm to find a fixed-length path that consists of a subset of the candidates as the localization result. Validation on a large-scale dataset of clinical CTs shows that our proposed method outperforms the state-of-art CI electrode localization methods and achieves a mean error of 0.12 mm when compared to expert manual localization results. This represents a crucial step in translating IGCIP from the laboratory to large-scale clinical use.

Scalar localisation of peri-modiolar electrodes and speech perception outcomes

OBJECTIVE

To identify the intracochlear electrode position in cochlear implant recipients and determine the correlation to speech perception for two peri-modiolar electrode arrays.

METHODS

Post-operative cone-beam computed tomography images of 92 adult recipients of the 'CI512' electrode and 18 adult recipients of the 'CI532' electrode were analysed. Phonemes scores were recorded pre-implantation, and at 3 and 12 months post-implantation.

RESULTS

All CI532 electrodes were wholly within scala tympani. Of the 79 CI512 electrodes intended to be in scala tympani, 58 (73 per cent) were in scala tympani, 14 (17 per cent) were translocated and 7 (9 per cent) were wholly in scala vestibuli. Thirteen CI512 electrodes were deliberately inserted into scala vestibuli. Speech perception scores for post-lingual recipients were higher in the scala tympani group (69.1 per cent) compared with the scala vestibuli (54.2 per cent) and translocation (50 per cent) groups (p < 0.05). Electrode location outside of scala tympani independently resulted in a 10.5 per cent decrease in phoneme scores.

CONCLUSION

Cone-beam computed tomography was valuable for demonstrating electrode position. The rate of scala tympani insertion was higher in CI532 than in CI512 electrodes. Scala vestibuli insertion and translocation were associated with poorer speech perception outcomes.

Automatic localization of closely spaced cochlear implant electrode arrays in clinical CTs

PURPOSE

Cochlear implants (CIs) are neural prosthetic devices that provide a sense of sound to people who experience profound hearing loss. Recent research has indicated that there is a significant correlation between hearing outcomes and the intracochlear locations of the electrodes. We have developed an image-guided cochlear implant programming (IGCIP) system based on this correlation to assist audiologists with programming CI devices. One crucial step in our IGCIP system is the localization of CI electrodes in postimplantation CTs. Existing methods for this step are either not fully automated or not robust. When the CI electrodes are closely spaced, it is more difficult to identify individual electrodes because there is no intensity contrast between them in a clinical CT. The goal of this work is to automatically segment the closely spaced CI electrode arrays in postimplantation clinical CTs.

METHODS

The proposed method involves firstly identifying a bounding box that contains the cochlea by using a reference CT. Then, the intensity image and the vesselness response of the VOI are used to segment the regions of interest (ROIs) that may contain the electrode arrays. For each ROI, we apply a voxel thinning method to generate the medial axis line. We exhaustively search through all the possible connections of medial axis lines. For each possible connection, we define CI array centerline candidates by selecting two points on the connected medial axis lines as the array endpoints. For each CI array centerline candidate, we use a cost function to evaluate its quality, and the one with the lowest cost is selected as the array centerline. Then, we fit an a priori known geometric model of the array to the centerline to localize the individual electrodes. The method was trained on 28 clinical CTs of CI recipients implanted with three models of closely spaced CI arrays. The localization results are compared with the ground truth localization results manually generated by an expert.

RESULTS

A validation study was conducted on 129 clinical CTs of CI recipients implanted with three models of closely spaced arrays. Ninety-eight percent of the localization results generated by the proposed method had maximum localization errors lower than one voxel diagonal of the CTs. The mean localization error was 0.13 mm, which was close to the rater's consistency error (0.11 mm). The method also outperformed the existing automatic electrode localization methods in our validation study.

CONCLUSION

Our validation study shows that our method can localize closely spaced CI arrays with an accuracy close to what is achievable by an expert on clinical CTs. This represents a crucial step toward automating IGCIP and translating it from the laboratory to the clinical workflow.

Evaluation of Outcome Variability Associated With Lateral Wall, Mid-scalar, and Perimodiolar Electrode Arrays When Controlling for Preoperative Patient Characteristics

OBJECTIVE

Determine the impact of electrode array selection on audiometric performance when controlling for baseline patient characteristics.

STUDY DESIGN

Retrospective evaluation of a prospective cochlear implant (CI) database (January 1, 2012-May 31, 2017).

SETTING

Tertiary Care University Hospital.

PATIENTS

Three hundred twenty-eight adult CI recipients.

INTERVENTIONS/MAIN OUTCOMES MEASURED

Hearing outcomes were measured through unaided/aided pure tone thresholds and speech recognition testing before and after cochlear implantation. All reported postoperative results were performed at least 6 months after CI activation. All device manufacturers were represented.

RESULTS

Of the 328 patients, 234 received lateral wall (LW) arrays, 46 received perimodiolar (PM) arrays, and 48 received mid-scalar (MS) arrays. Patients receiving PM arrays had significantly poorer preoperative earphone and aided PTAs and SRTs, and aided Consonant-Nucleus-Consonant(CNC) word and AzBio +10 SNR scores compared with patients receiving LW arrays (all p ≤ 0.04), and poorer PTAs and AzBio +10 SNR scores compared with MS recipients (all p ≤ 0.02). No preoperative audiological variables were found to significantly differ between MS and LW patients. After controlling for preoperative residual hearing and speech recognition ability in a hierarchical multiple regression analysis, no statistically significant difference in audiological outcomes was detected (CNC words, AzBio quiet, or AzBio +10 SNR) among the three electrode array types (all p > 0.05).

CONCLUSION

While previous studies have demonstrated superior postoperative speech recognition scores in LW electrode array recipients, these differences lose significance when controlling for baseline hearing and speech recognition ability. These data demonstrate the proclivity for implanting individuals with greater residual hearing with LW electrodes and its impact on postoperative results.

Automatic classification of cochlear implant electrode cavity positioning

Cochlear Implants (CIs) restore hearing using an electrode array that is surgically implanted into the intra-cochlear cavities. Research has indicated that each electrode can lie in one of several cavities and that location is significantly associated with hearing outcomes. However, comprehensive analysis of this phenomenon has not been possible because the cavities are not directly visible in clinical CT images and because existing methods to estimate cavity location are not accurate enough, labor intensive, or their accuracy has not been validated. In this work, a novel graph-based search is presented to automatically identify the cavity in which each electrode is located. We test our approach on CT scans from a set of 34 implanted temporal bone specimens. High resolution μCT scans of the specimens, where cavities are visible, show our method to have 98% cavity classification accuracy. These results indicate that our methods could be used on a large scale to study the link between electrode placement and outcome, which could lead to advances that improve hearing outcomes for CI users.

Early Outcomes With a Slim, Modiolar Cochlear Implant Electrode Array

OBJECTIVE

To describe outcomes from cochlear implantation with a new, slim modiolar electrode array.

STUDY DESIGN

Retrospective cohort study.

SETTING

Tertiary referral centers.

PATIENTS

Adult cochlear implant candidates.

INTERVENTIONS

Cochlear implantation with CI532 (Cochlear Corp).

MAIN OUTCOME MEASURES

Pre- and postoperative speech perception scores, operative details, and postoperative computed tomography (CT) reconstructions of array location.

RESULTS

One hundred seventeen patients are implanted to date. There were eight tip rollovers identified with intraoperative x-ray and resolved with reinsertion. An additional rollover was identified on postoperative CT. CT reconstructions in 17 of 23 patients showed complete scala tympani placement with a wrap factor of 58% (range 53-64%) and a mean insertion angle of 406 degrees (range 360-452 degrees). Three implants demonstrated array translocation with electrodes in the scala vestibuli. Consonant-nucleus-consonant word scores improved from 10% preoperatively to 48% at 3 months postoperatively. Pure-tone thresholds were preserved postoperatively in 37 to 52% of patients across frequencies from 250 to 4000 Hz. Functional pure-tone thresholds (≤80 dB) were recorded in 9 to 25% of patients.

CONCLUSION

CI532 array insertion results in consistent scala tympani location and provides expected audiologic performance. Initial hearing preservation results are not consistent with current electro-acoustic arrays.

Validation of automatic cochlear implant electrode localization techniques using μ CTs

Cochlear implants (CIs) are standard treatment for patients who experience sensorineural hearing loss. Although these devices have been remarkably successful at restoring hearing, it is rare that they permit to achieve natural fidelity and many patients experience poor outcomes. Our group has developed image-guided CI programming techniques (IGCIP), in which image analysis techniques are used to locate the intracochlear position of CI electrodes to determine patient-customized settings for the CI processor. Clinical studies have shown that IGCIP leads to significantly improved outcomes. A crucial step is the localization of the electrodes, and rigorously quantifying the accuracy of our algorithms requires dedicated datasets. We discuss the creation of a ground truth dataset for electrode position and its use to evaluate the accuracy of our electrode localization techniques. Our final ground truth dataset includes 30 temporal bone specimens that were each implanted with one of four different types of electrode array by an experienced CI surgeon. The arrays were localized in conventional CT images using our automatic methods and manually in high-resolution μ CT images to create the ground truth. The conventional and μ CT images were registered to facilitate comparison between automatic and ground truth electrode localization results. Our technique resulted in mean errors of 0.13 mm in localizing the electrodes across 30 cases. Our approach successfully permitted characterizing the accuracy of our methods, which is critical to understand their limitations for use in IGCIP.

Effect of frequency mismatch and band partitioning on vocal tract length perception in vocoder simulations of cochlear implant processing

The vocal tract length (VTL) of a speaker is an important voice cue that aids speech intelligibility in multi-talker situations. However, cochlear implant (CI) users demonstrate poor VTL sensitivity. This may be partially caused by the mismatch between frequencies received by the implant and those corresponding to places of stimulation along the cochlea. This mismatch can distort formant spacing, where VTL cues are encoded. In this study, the effects of frequency mismatch and band partitioning on VTL sensitivity were investigated in normal hearing listeners with vocoder simulations of CI processing. The hypotheses were that VTL sensitivity may be reduced by increased frequency mismatch and insufficient spectral resolution in how the frequency range is partitioned, specifically where formants lie. Moreover, optimal band partitioning might mitigate the detrimental effects of frequency mismatch on VTL sensitivity. Results showed that VTL sensitivity decreased with increased frequency mismatch and reduced spectral resolution near the low frequencies of the band partitioning map. Band partitioning was independent of mismatch, indicating that if a given partitioning is suboptimal, a better partitioning might improve VTL sensitivity despite the degree of mismatch. These findings suggest that customizing the frequency partitioning map may enhance VTL perception in individual CI users.

Imaging evaluation of electrode placement and effect on electrode discrimination on different cochlear implant electrode arrays

OBJECTIVE

The aim of the present study is to evaluate the effect of electrode discrimination based on electrode to modiolus distance in different cochlear implant models, using image information to estimate the outcomes after an implantation on electrode discrimination METHODS: A descriptive prospective randomized study performed during 16 months. A psychoacoustic platform was used to evaluate patients' electrode discrimination capabilities of patients. For the acquisition of the images, a cone beam computed tomography was used to assess postcochlear implantation of electrodes' position. We considered two other new measurements: the intracochlear position index, which indicates how far is the electrode from the modiolar wall, and the homogeneity factor (HF), which provides us with information about the distance between the electrodes and the modiolus RESULTS: 21 postlingually deaf adults showing different CI models [CI522 (n = 7), CI512 (n = 7), and CI532 (n = 7)] that corresponded to the lateral and perimodiolar array electrodes. The average success rate of the CI522 group was 47%, of the CI512 group was 48%, and of the CI532 group was 77%. There is statistically significant difference between groups CI532-CI522 (p = 0.0033) and CI532-CI512 (p = 0.0027) CONCLUSION: The Nucleus CI532 offers a better perimodiolar placement. HF and IPI measurements provide information about the electrodes location inside the cochlea, being related to electrode discrimination.

Minimum Reporting Standards for Adult Cochlear Implantation

This article outlines new minimum standards for reporting adult cochlear implant outcomes. These standards have been endorsed by the Implantable Hearing Devices Committee and the Hearing Committee of the American Academy of Otolaryngology-Head and Neck Surgery. The lack of a standardized method for reporting outcomes following cochlear implantation in clinical trials has hampered the ability of investigators to draw comparisons across studies. Variability in data reported in articles and presentation formats inhibits meta-analyses, making it impossible to accumulate the large patient cohorts needed for statistically significant inference. While investigators remain unrestricted in publishing their adult cochlear implant outcome data in additional formats that they believe to be valuable, they should include the presently proposed minimal data set to facilitate interstudy comparability and consistency of reporting.

Comparison of cochlear duct length between the Saudi and non-Saudi populations

BACKGROUND

There are no data on cochlear duct lengths (CDL) among Middle East populations.

OBJECTIVES

The main aims of this study were to estimate the average CDL in the Saudi population and to compare it with the reported CDL in other regions/ethnic groups outside the Middle East.

DESIGN

Retrospective study.

SETTING

Tertiary otolaryngology head and neck surgery center.

SUBJECTS AND METHODS

Temporal bone CT scans were reviewed to determine CDL. We excluded any CT scan of an ear with a congenital inner ear anomaly or acquired pathology.

MAIN OUTCOME MEASURES

CDL.

SAMPLE SIZE

441 temporal bone CT scans.

RESULTS

The overall CDL mean was 31.9 mm (range 20.3-37.7 mm). The cochleae of males was significantly longer than of females and cochleae from the left side were significantly longer than of the right side. No significant difference was found between children and adults. Inter-study comparison revealed a significant difference in CDL between the Saudi population in our study and European and Australian studies, but not between the present study and North American studies.

CONCLUSIONS

The CDL differed significantly according to side of the cochlea and sex, but not by age. Geographically and ethnically, the mean CDL for Saudis was significantly different from the CDL of subjects of some ethnic backgrounds, but not others. Due to this diversity, we recommend that the CDL be measured before cochlear implant surgery.

LIMITATIONS

All the measurements were done by one person, and the subjects' physical measurements, such as height or head circumference, were not included.

CONFLICT OF INTEREST

None.

Intraoperative Conebeam CT for Assessment of Intracochlear Positioning of Electrode Arrays in Adult Recipients of Cochlear Implants

BACKGROUND AND PURPOSE

Intraoperative conebeam CT has been introduced into the operating room and provides quick radiologic feedback. This study aimed to investigate its utility in the assessment of the positioning of the electrode array after cochlear implantation.

MATERIALS AND METHODS

This was a retrospective study of 51 patients (65 ears) with intraoperative imaging by conebeam CT (O-arm) after cochlear implantation between 2013 and 2017. Correct placement into the cochlea was immediately identified. Positioning assessments were later analyzed with OsiriX software.

RESULTS

Intraoperative imaging was quickly performed in all cases. No misplacement into the vestibule or semicircular canals was found. A foldover of the implanted array was identified in 1 patient. Secondary analysis by 2 raters showed excellent agreement on insertion depth angle (intraclass correlation = 0.96, P < .001) and length of insertion of the electrode array (intraclass correlation coefficient = 0.93, P = .04) measurements. The evaluation of the number of extracochlear electrodes was identical between the 2 raters in 78% of cases (Cohen κ = 0.55, P < .001). The scalar position was inconsistent between raters. When we compared O-arm and high-resolution CT images in 14 cases, the agreement was excellent for insertion depth angle (intraclass correlation coefficient = 0.97, P < .001) and insertion length (intraclass correlation coefficient = 0.98, P < .001), good for the number of extracochlear electrodes (Cohen κ = 0.63, P = .01), but moderate for the scalar position (Cohen κ = 0.59, P = .02).

CONCLUSIONS

Intraoperative conebeam CT using the O-arm is a safe, rapid, easy, and reliable procedure to immediately identify a misplacement or foldover of an electrode array. The insertion depth angle, insertion length, and number of electrodes inserted can be accurately assessed.

Tip Fold-over in Cochlear Implantation: Case Series

OBJECTIVE

To describe the incidence, clinical presentation, and performance of cochlear implant (CI) recipients with tip fold-over.

STUDY DESIGN

Retrospective case series.

SETTING

Tertiary referral center.

PATIENTS

CI recipients who underwent postoperative computed tomography (CT) scanning.

INTERVENTION(S)

Tip fold-over was identified tomographically using previously validated software that identifies the electrode array. Electrophysiologic testing including spread of excitation or electric field imaging (EFI) was measured on those with fold-over.

MAIN OUTCOME MEASURE(S)

Location of the fold-over; audiological performance pre and postselective deactivation of fold-over electrodes.

RESULTS

Three hundred three ears of 235 CI recipients had postoperative CTs available for review. Six (1.98%) had tip fold-over with 5/6 right-sided ears. Tip fold-over occurred predominantly at 270 degrees and was associated with precurved electrodes (5/6). Patients did not report audiological complaints during initial activation. In one patient, the electrode array remained within the scala tympani with preserved residual hearing despite the fold-over. Spread of excitation supported tip fold-over, but the predictive value was not clear. EFI predicted location of the fold-over with clear predictive value in one patient. At an average follow-up of 11 months, three subjects underwent deactivation of the overlapping electrodes with two of them showing marked audiological improvement.

CONCLUSION

In a large academic center with experienced surgeons, tip fold-over occurred at a rate of 1.98% but was not immediately identifiable clinically. CT imaging definitively showed tip fold-over. Deactivating involved electrodes may improve performance possibly avoiding revision surgery. EFI may be highly predictive of tip fold-over and can be run intraoperatively, potentially obviating the need for intraop fluoroscopy.

Initial Operative Experience and Short-term Hearing Preservation Results With a Mid-scala Cochlear Implant Electrode Array

OBJECTIVE

To describe our initial operative experience and hearing preservation results with the Advanced Bionics (AB) Mid Scala Electrode (MSE).

STUDY DESIGN

Retrospective review.

SETTING

Tertiary referral center.

PATIENTS

Sixty-three MSE implants in pediatric and adult patients were compared with age- and sex-matched 1j electrode implants from the same manufacturer. All patients were severe to profoundly deaf.

INTERVENTION

Cochlear implantation with either the AB 1j electrode or the AB MSE.

MAIN OUTCOME MEASURES

The MSE and 1j electrodes were compared in their angular depth of insertion and pre to postoperative change in hearing thresholds. Hearing preservation was analyzed as a function of angular depth of insertion. Secondary outcome measures included operative time, incidence of abnormal intraoperative impedance and telemetry values, and incidence of postsurgical complications.

RESULTS

Depth of insertion was similar for both electrodes, but was more consistent for the MSE array and more variable for the 1j array. Patients with MSE electrodes had better hearing preservation. Thresholds shifts at four audiometric frequencies ranging from 250 to 2000 Hz were 10, 7, 2, and 6 dB smaller for the MSE electrode than for the 1j (p < 0.05). Hearing preservation at low frequencies was worse with deeper insertion, regardless of array. Secondary outcome measures were similar for both electrodes.

CONCLUSION

The MSE electrode resulted in more consistent insertion depth and somewhat better hearing preservation than the 1j electrode. Differences in other surgical outcome measures were small or unlikely to have a meaningful effect.

Factors Affecting Outcomes in Cochlear Implant Recipients Implanted With a Perimodiolar Electrode Array Located in Scala Tympani

OBJECTIVE

To identify primary biographic and audiologic factors contributing to cochlear implant (CI) performance variability in quiet and noise by controlling electrode array type and electrode position within the cochlea.

BACKGROUND

Although CI outcomes have improved over time, considerable outcome variability still exists. Biographic, audiologic, and device-related factors have been shown to influence performance. Examining CI recipients with consistent array type and electrode position may allow focused investigation into outcome variability resulting from biographic and audiologic factors.

METHODS

Thirty-nine adults (40 ears) implanted for at least 6 months with a perimodiolar electrode array known (via computed tomography [CT] imaging) to be in scala tympani participated. Test materials, administered CI only, included monosyllabic words, sentences in quiet and noise, and spectral ripple discrimination.

RESULTS

In quiet, scores were high with mean word and sentence scores of 76 and 87%, respectively; however, sentence scores decreased by an average of 35 percentage points when noise was added. A principal components (PC) analysis of biographic and audiologic factors found three distinct factors, PC1 Age, PC2 Duration, and PC3 Pre-op Hearing. PC1 Age was the only factor that correlated, albeit modestly, with speech recognition in quiet and noise. Spectral ripple discrimination strongly correlated with speech measures.

CONCLUSION

For these recipients with consistent electrode position, PC1 Age was related to speech recognition performance. Consistent electrode position may have contributed to high speech understanding in quiet. Inter-subject variability in noise may have been influenced by auditory/cognitive processing, known to decline with age, and mechanisms that underlie spectral resolution ability.

Electrode Location and Angular Insertion Depth Are Predictors of Audiologic Outcomes in Cochlear Implantation

OBJECTIVES

1) Investigate the impact of electrode type and surgical approach on scalar electrode location; and 2) examine the relation between electrode location and postoperative audiologic performance.

SETTING

Tertiary academic hospital.

PATIENTS

Two hundred twenty post-lingually deafened adults undergoing cochlear implant (CI).

MAIN OUTCOME MEASURES

Primary outcome measures of interest were scalar electrode location and postoperative audiologic performance.

RESULTS

In 68% of implants, electrodes were observed to be located solely in the scala tympani (ST). Multivariate analysis demonstrated perimodiolar (PM) and mid-scala (MS) electrodes were 22.4 (95% CI: 6.3-80.0, p < 0.001) and 55.0 (95% CI: 9.7-312.8, p < 0.001) times more likely to have at least one electrode in the scala vestibuli (SV) compared with lateral wall (LW) electrodes, respectively. Compared with cochleostomy (C), round window (RW) and extended round window (ERW) approaches demonstrated 70% reduction in SV insertion (RW: OR 0.28, 95% CI: 0.1-0.8, p = 0.01; ERW: OR 0.28, 95% CI: 0.1-0.7, p = 0.005). Examining postoperative audiometric performance, consonant-nucleus-consonant (CNC) score increased 0.6% with every 10 degrees increase in angular insertion depth beyond the group minimum of 208 degrees (coefficient 0.0006, 95% CI: 0.0001-0.001, p = 0.03). SV insertion was associated with a 12% decrease in CNC score (coefficient -0.12, 95% CI: -0.22 to -0.02, p = 0.02). CNC score decreased 0.3% for every 1 year increase in age (coefficient -0.003, 95% CI: -0.006 to -0.0006, p = 0.02).

CONCLUSIONS

Electrode design and surgical approach were predictors of scalar electrode location. Specifically, LW electrodes showed higher rates of ST insertion compared with PM or MS. RW and ERW approaches showed higher rates of ST insertion when compared with C. In regards to performance, ST insertion, younger age, and greater angular insertion depth were predictors of improved CNC scores.

Evaluation of Rigid Cochlear Models for Measuring Cochlear Implant Electrode Position

OBJECTIVE

To investigate the accuracy of rigid cochlear models in measuring intra-cochlear positions of cochlear implant (CI) electrodes.

PATIENTS

Ninety three adults who had undergone CI and pre- and postoperative computed tomographic (CT) imaging.

MAIN OUTCOME MEASURES

Seven rigid models of cochlear anatomy were constructed using micro-CTs of cochlear specimens. Using each of the seven models, the position of each electrode in each of the 98 ears in our dataset was measured as its depth along the length of the cochlea, its distance to the basilar membrane, and its distance to the modiolus. Cochlear duct length was also measured using each model.

RESULTS

Standard deviation (SD) across rigid cochlear models in measures of electrode depth, distance to basilar membrane, distance to modiolus, and length of the cochlear duct at two turns were 0.68, 0.11, 0.15, and 1.54 mm. Comparing the estimated position of the electrodes with respect to the basilar membrane, i.e., deciding whether an electrode was located within the scala tympani (ST) or the scala vestibuli (SV), there was not a unanimous agreement between the models for 19% of all the electrodes. With respect to the modiolus, each electrode was classified into one of the three groups depending on its modiolar distance: close, medium, and far. Rigid models did not unanimously agree on modiolar distance for approximately 50% of the electrodes tested.

CONCLUSIONS

Inter-model variance of rigid cochlear models exists, demonstrating that measurements made using rigid cochlear models are limited in terms of accuracy because of non-rigid inter-subject variations in cochlear anatomy.

Hearing Changes After Intratympanically Applied Steroids for Primary Therapy of Sudden Hearing Loss: A Meta-analysis Using Mathematical Simulations of Drug Delivery Protocols

OBJECTIVE

Controlled and uncontrolled studies with primary intratympanic or combined intratympanic and systemic application of glucocorticosteroids for idiopathic sudden hearing loss were analyzed by means of a meta-analysis in an attempt to establish optimal local drug delivery protocols.

STUDY DESIGN

A total of 25 studies with 28 treatment groups between January 2000 and June 2014 were selected that adequately described drug delivery protocols. Cochlear drug levels were calculated by a validated computer model of drug dispersion in the inner ear fluids based on the concentration and volume of glucocorticoids applied, the time the drug remained in the middle ear, and the specific timing of injections. Various factors were compared with hearing outcome, including baseline data, individual parameters of the application protocols, calculated peak concentration (Cmax), and total dose (area under the curve).

RESULTS

There was no dependence of hearing outcome on individual parameters of the application protocol, Cmax, or area under the curve. Final hearing threshold was notably independent of delay of treatment.

CONCLUSION

During primary intratympanic or combined steroid therapy of idiopathic sudden hearing loss, the tendency toward early treatment having a positive effect on hearing improvement is thought to be a "sham effect," likely related to spontaneous recovery. Change in pure-tone average may not be an adequate outcome parameter to assess effectiveness of the intervention, as it depends on the degree of initial hearing loss. Final pure-tone average provides a better alternative.

Contemporary imaging of auditory implants

There have been significant advances in the diversity and effectiveness of hearing technologies in recent years. Implanted auditory devices may be divided into those that stimulate the cochlear hair cells (bone conduction devices and middle ear implants), and those that stimulate the neural structures (cochlear implants and central auditory implants). Contemporary preoperative and postoperative imaging may be used to help individualise implant selection, optimise surgical technique and predict auditory outcome. This review will introduce the concepts behind auditory implants, and explains how imaging is increasingly used to aid insertion and evaluation of these devices.

Cochlear duct length-one size fits all?

OBJECTIVE

Recent studies demonstrated the utility of high-resolution computed tomography (HRCT) scans in measuring basal cochlear length and cochlear insertion depths. These studies showed significant variations in the anatomy of the cochlea amongst humans. The aim of our study was to investigate for gender and racial variations in the basal turn length of the human cochlea in an Asian population.

METHOD

HRCT temporal bone data from year 1997 till 2012 of patients with normally developed cochleae who reported with otologic disease was obtained. Reconstruction of the full basal turn was performed for both ears. The largest distance from the midpoint of the round window, through the midmodiolar axis, to the lateral wall was measured (distance A). Length of the lateral wall of the cochlea to the first turn (360°) was calculated and statistically analyzed.

RESULTS

HRCT temporal bone data from 161 patients was initially obtained. Four patients were subsequently excluded from the study as they were of various other racial groups. Study group therefore comprised of 157 patients (314 cochleae). Mean distance A was statistically different between the two sides of the ear (right 9.09mm; left 9.06mm; p=0.0069). Significant gender and racial differences were also found. Mean distance A was 9.17mm in males and 8.97mm in females (p=0.0016). The racial groups were Chinese (39%), Malay (38%) and Indian (22%). Between racial groups, mean distance A was 9.11mm (Chinese), 9.11mm (Malays) and 8.99mm (Indians). The mean basal turn lengths ranged from 19.71mm to 25.09mm. With gender factored in, significant variation in mean basal turn lengths was found across all three racial groups (p=0.04).

CONCLUSION

The view of the basal turn of the cochlea from HRCT is simple to obtain and reproducible. This study found significant differences in basal cochlear length amongst male and female Asian patients, as well as amongst various racial groups. This has implications for cochlear electrode insertion as well as electrode array design.

Plasticity in bilateral superior temporal cortex: Effects of deafness and cochlear implantation on auditory and visual speech processing

While many individuals can benefit substantially from cochlear implantation, the ability to perceive and understand auditory speech with a cochlear implant (CI) remains highly variable amongst adult recipients. Importantly, auditory performance with a CI cannot be reliably predicted based solely on routinely obtained information regarding clinical characteristics of the CI candidate. This review argues that central factors, notably cortical function and plasticity, should also be considered as important contributors to the observed individual variability in CI outcome. Superior temporal cortex (STC), including auditory association areas, plays a crucial role in the processing of auditory and visual speech information. The current review considers evidence of cortical plasticity within bilateral STC, and how these effects may explain variability in CI outcome. Furthermore, evidence of audio-visual interactions in temporal and occipital cortices is examined, and relation to CI outcome is discussed. To date, longitudinal examination of changes in cortical function and plasticity over the period of rehabilitation with a CI has been restricted by methodological challenges. The application of functional near-infrared spectroscopy (fNIRS) in studying cortical function in CI users is becoming increasingly recognised as a potential solution to these problems. Here we suggest that fNIRS offers a powerful neuroimaging tool to elucidate the relationship between audio-visual interactions, cortical plasticity during deafness and following cochlear implantation, and individual variability in auditory performance with a CI.

Radiological and NRT-Ratio-Based Estimation of Slim Straight Cochlear Implant Electrode Positions: A Multicenter Study

OBJECTIVES

An intraoperative neural response telemetry-ratio (NRT-ratio) was established, which can provide information about the intraoperative intracochlear electrode array position for perimodiolar electrodes.

METHODS

In a retrospective controlled study in 2 tertiary referral centers, the electrophysiological data sets of 50 patients with measured intraoperative auto-NRTs and postoperative radiological examinations were evaluated. All patients were implanted with Nucleus slim straight electrodes. The NRT-ratio was calculated by dividing the average auto-NRT data from electrodes 16 to 18 with the average from electrodes 5 to 7. Using a flat panel tomography system or a computed tomography, the position of the electrode array was certified radiological.

RESULTS

Radiologically, 2 out of 50 patients were identified with an electrode translocated from the scala tympani into the scala vestibuli. The radiologically estimated electrodes indicating a scalar change showed a regular NRT-ratio but nonspecific NRT-level changes at the localization of translocation.

Multicenter surgical experience evaluation on the Mid-Scala electrode and insertion tools

The HiFocus Mid-Scala electrode is intended to improve hearing for individuals with severe-to-profound hearing loss by providing extended electrical coverage of the cochlea while minimizing trauma related to insertion. The electrode is appropriate for use with a wide range of surgical techniques, including either a cochleostomy or round window insertion, and the use of either a free-hand or tool-assisted approach. The objective of this survey was to evaluate how the HiFocus Mid-Scala electrode and insertion tools was used across a population of cochlear implant recipients of differing ages, audiologic profiles, and anatomical characteristics. The intent was to understand the type and frequency of surgical techniques applicable with the electrode, and to provide guidelines for clinical practice. Two questionnaires were completed by surgeons at implant centres located in the United States, Europe, and Asia. Before any surgeries were conducted, surgeons completed a questionnaire that assessed their overall cochlear implant surgical practice and preferences. Following each HiFocus Mid-Scala electrode insertion, surgeons completed a questionnaire that summarized their experience during that surgical procedure. Questionnaires were completed by 32 surgeons from 16 centres for a total of 143 surgeries (112 adults, 31 children). Most surgeons (62 %) preferred to insert the electrode via the round window or an extended round window compared with a cochleostomy (16 %), whereas the remaining 22 % indicated that they made an insertion choice based on presenting anatomy. Sixty-nine percent preferred a free-hand approach over using insertion tools. In 32 procedures, surgeons elected to deviate from an intended round window insertion to either an extended round window or cochleostomy approach.

The Role of Electrode Placement in Bilateral Simultaneously Cochlear-Implanted Adult Patients

Objective

To evaluate the influence of the electrode placement on hearing performance in adult patients who were simultaneously and bilaterally cochlear implanted.

Study Design

Case series with planned data collection.

Setting

Tertiary referral university centers.

Subjects and Methods

The postoperative computed tomography scan was studied for 19 patients who were simultaneously and bilaterally implanted with a long straight electrode array. The size of the cochlea was measured in consideration of the major cochlear diameter and cochlear height. The electrode-to-modiolus distance for the electrodes positioned at 180 and 360 degrees and the angular depth of insertion of the array were also measured. Speech perception was assessed at 1 and 5 years postimplantation with disyllabic word lists in quiet and in noise, with the speech coming from the front and a background noise (cocktail party) coming from 5 loudspeakers.

Results

At 1 year postimplantation, the electrode-to-modiolus distance at 180 degrees was correlated with the speech perception scores in both quiet and noise. In patients with a full electrode insertion, no correlation was found between the angular depth of insertion and hearing performance. The speech perception scores in noise gradually declined as a function of the number of inserted and active electrodes. No relationship between electrode position and speech perception scores was found at 5 years postimplantation.

Conclusion

In adult patients who were simultaneously and bilaterally implanted, the use of a long straight array, the full electrode array insertion, and the proximity to the modiolus might be determining factors to obtain the best speech performance at 1 year, without influence on the speech perception scores after long-term use.

Measurement of Cochlear Implant Electrode Position From Intraoperative Post-insertion Skull Radiographs: A Validation Study

OBJECTIVE

To validate a method of measuring angular depth of insertion (aDOI) as well as positional depth of each electrode contact in a cochlear implant by using intraoperative postinsertion skull radiographs.

STUDY DESIGN

Retrospective review.

SETTING

Tertiary referral center.

PATIENTS

Intraoperative postinsertion radiographs obtained from 18 cochlear implant recipients were chosen for analysis. One high-resolution computer tomography scan of the head with the electrode in place was also analyzed. One cadaveric temporal bone with an inserted electrode provided additional data for analysis.

INTERVENTION

aDOI and position of each electrode contact were measured from the radiographs using readily available software. High-resolution computer tomography imaging of the cochlea and electrode were reconstructed in three dimensions and used to simulate head rotation during intraoperative radiographs. The cadaveric temporal bone was imaged by x-ray at various acquisition angles.

MAIN OUTCOME MEASURES

We evaluated the error introduced in measuring aDOI by assessing intra- and inter-rater variability. We also evaluated the error introduced by x-ray acquisition at nonstandardized angles by analyzing the three-dimensional construct and the cadaveric temporal bone.

RESULTS

The concordance correlation coefficients for intrarater (0.991) and inter-rater (0.996) variability in aDOI measurement were excellent. The error introduced by nonstandardized x-ray acquisition angles was only -12.5 degrees to +15.8 degrees even at the limits of clinically relevant head rotation.

CONCLUSIONS

The intraoperative postinsertion radiograph is sufficient for estimating positional depth of electrode contacts and the aDOI. This measure is robust in the face of nonstandardized x-ray acquisition angles, and shows good intra- and inter-rater variability.

Intraoperative Electrophysiologic Variations Caused by the Scalar Position of Cochlear Implant Electrodes

OBJECTIVE

The position of cochlear implant (CI) electrodes in the cochlea is fundamental for the interaction between the implant and the neurons of the spiral ganglion. The scalar position of the electrode in the cochlea is assumed to be an important parameter for the clinical outcome. In our study, the intraoperative electrophysiologic characteristics in dependence of the position of CI electrodes in the scala tympani or in the scala vestibuli after scalar change should be determined.

MATERIALS AND METHODS

The intraoperative impedances and neural response telemetry (NRT) data of 23 patients implanted with a Nucleus Advance Contour (Cochlear Pty, Sydney, Australia) electrode were recorded. One CI surgeon and two radiologists evaluated the electrode array's position independently radiologically by flat-panel tomography. Results from 17 patients with the electrode positioned in the scala tympani and six patients with the electrode changing intraoperatively from the tympanic into the vestibular scala were retrospectively analyzed.

RESULTS

We found a statistically significant difference with an NRT threshold-based ratio for the groups. An estimation of the (radiologically confirmed) scalar position based on the NRT ratio was possible retrospectively.

CONCLUSION

The evaluation of specific intraoperative electrophysiologic data allowed separating between a regular and an irregular (i.e., scalar changing) position of CI electrodes. This noninvasive methodology can support the postoperative radiologic evaluation of the CI electrode array position.

Cone-beam CT versus multi-slice CT systems for postoperative imaging of cochlear implantation--a phantom study on image quality and radiation exposure using human temporal bones

HYPOTHESIS

Image quality of low-dose multi-slice computed tomography (MSCT) after cochlear implantation is comparable to that of cone-beam computed tomography (CBCT).

BACKGROUND

CBCT has been described as a low-dose alternative with superior image quality to MSCT for postoperative cochlear implant (CI) imaging, but to our knowledge, no dose-matched comparisons of image quality have been published.

MATERIALS AND METHODS

Five human cochleae were implanted with CI electrodes and scanned on two CBCT and two MSCT systems. Four independent observers rated aspects of image quality on a five-point scale. CBCT scans were compared to clinical and dose-matched MSCT scans. Declining-dose MSCT protocols were compared to the clinical protocol. CT phantoms were used to determine effective dose and resolution for each acquisition protocol.

RESULTS

Effective dose of the CBCT protocols was 6 to 16% of the clinical MSCT dose. Visibility of cochlear inner and outer walls and overall image quality were positively correlated with radiation dose on MSCT and image quality was better with clinical MSCT than with CBCT protocols. In other comparisons, differences between systems were found, but a distinction between CBCT and MSCT could not be made.

CONCLUSION

CBCT and dose-matched MSCT are both suitable for postoperative CI imaging. Selecting a CT system and radiation dose depends on which cochlear structures need to be visualized.

Automatic graph-based localization of cochlear implant electrodes in CT

Cochlear Implants (CIs) restore hearing using an electrode array that is surgically implanted into the cochlea. Research has indicated there is a link between electrode location within the cochlea and hearing outcomes, however, comprehensive analysis of this phenomenon has not been possible because techniques proposed for locating electrodes only work for specific implant models or are too labor intensive to be applied on large datasets. We present a general and automatic graph-based method for localizing electrode arrays in CTs that is effective for various implant models. It relies on a novel algorithm for finding an optimal path of fixed length in a graph and achieves maximum localization errors that are sub-voxel. These results indicate that our methods could be used on a large scale to study the link between electrode placement and outcome across electrode array types, which could lead to advances that improve hearing outcomes for CI users.

The use of cone-beam computed tomography to determine cochlear implant electrode position in human temporal bones

OBJECTIVE

To assess the utility of cone-beam computed tomography (CBCT) imaging in the estimation of cochlear implant (CI) electrode position in implanted temporal bones.

STUDY DESIGN

Eight fresh frozen temporal bones were mounted and oriented as for standard surgery and were implanted with Cochlear Slim-Straight (SS) or Contour Advance electrode arrays by 2 CI surgeons. The bones were then imaged using an Accuitomo F170 CBCT scanner (isometric 250 μm voxel size) and were then processed for histologic sectioning (500 μm sections).

MAIN OUTCOME MEASURES

The CBCT images and the histologic micrographs (providing the "gold standard") were examined independently by several observers who assessed the scalar position (tympani or vestibuli) of each electrode in each temporal bone specimen.

RESULTS

Examination of the histologic micrographs confirmed that all electrodes were positioned within the scala tympani in all 8 bones. Similar judgments were made by the observers rating the CBCT images, except that one of the 2 observers estimated some of the apical electrodes to be located in the scala vestibuli in two of the bones implanted with the SS electrode.

CONCLUSION

Cone-beam CT imaging is able to provide a good indication of the scalar position of implanted electrodes, although estimation may be slightly less reliable for apical electrodes and for straight electrode designs. Additional advantages of using CBCT for this purpose are shorter acquisition time and reduction of radiation dose as compared with conventional CT.

Comparison of traditional histology and TSLIM optical sectioning of human temporal bones

HYPOTHESIS

Thin-sheet laser imaging microscopy (TSLIM) optical sectioning can be used to assess temporal bone soft tissue morphology before celloidin sectioning.

BACKGROUND

Traditional human temporal bone (TB) celloidin embedding and sectioning is a lengthy and involved process. Although bone morphology can be assessed with microCT before traditional histology, soft tissue structures are difficult to resolve until after celloidin sectioning. A potential solution is TSLIM, a high-resolution, nondestructive optical sectioning technique first developed to image bone and soft tissue in animal cochleae.

METHODS

Two temporal bones from 1 individual were used to evaluate TSLIM's capacity to image human temporal bones (bone and soft tissue) before traditional histology. The right TB was trimmed to the cochlea, prepared for and imaged with TSLIM, then processed for celloidin sectioning. The left TB, serving as a control, was directly prepared for traditional celloidin sectioning.

RESULTS

TSLIM imaging of the right TB showed adequate resolution of all major tissue structures but barely resolved cells. Celloidin sections produced from the TSLIM-imaged right TB were equivalent in cytologic detail to those from the traditionally prepared left TB. TSLIM 3-dimensional (3D) reconstructions were superior to those obtained from celloidin sections because TSLIM produced many more sections that were without mechanical sectioning artifacts or alignment issues.

CONCLUSION

TSLIM processing disturbs neither gross nor detailed morphology and integrates well with celloidin histology, making it an ideal method to image soft tissue before celloidin sectioning.

Conductive component after cochlear implantation in patients with residual hearing conservation

PURPOSE

Changes in auditory thresholds following cochlear implantation are generally assumed to be due to damage to neural elements. Theoretical studies have suggested that placement of a cochlear implant can cause a conductive hearing loss. Identification of a conductive component following cochlear implantation could guide improvements in surgical techniques or device designs. The purpose of this study is to characterize new-onset conductive hearing losses after cochlear implantation.

METHOD

In a prospective study, air- and bone-conduction audiometric testing were completed on cochlear implant recipients. An air-bone gap equal to or greater than 15 dB HL at 2 frequencies determined the presence of a conductive component.

RESULTS

Of the 32 patients with preoperative bone-conduction hearing, 4 patients had a new-onset conductive component resulting in a mixed hearing loss, with air-conduction thresholds ranging from moderate to profound and an average air-bone gap of 30 dB HL. One had been implanted through the round window, 2 had an extended round window, and 1 had a separate cochleostomy.

CONCLUSIONS

Loss of residual hearing following cochlear implantation may be due in part to a conductive component. Identifying the mechanism for this conductive component may help minimize hearing loss. Postoperative hearing evaluation should measure both air- and bone-conduction thresholds.

Cochleostomy versus round window insertions: influence on functional outcomes in electric-acoustic stimulation of the auditory system

OBJECTIVE

To assess the potential influence of 2 different surgical access routes to scala tympani for hearing preservation cochlear implantation on outcomes.

STUDY DESIGN

Retrospective review.

SETTING

Tertiary care academic center.

PATIENTS

Twenty adult subjects participating in a prospective clinical trial on electric-acoustic stimulation. Subjects underwent cochlear implantation with attempted hearing preservation and subsequent ipsilateral electric-acoustic stimulation of the auditory system.

INTERVENTIONS

Eight subjects (40%) were implanted using a round window-related cochleostomy and 12 subjects (60%) via a round window approach.

MAIN OUTCOME MEASURES

Postoperative acoustic hearing preservation and speech perception measures were obtained at defined intervals and compared for both groups with and without the use of the external speech processor.

RESULTS

The data demonstrate no statistically significant differences in postoperative outcomes for both preservation of residual hearing and unaided and aided speech perception between the cochleostomy and round window groups.

CONCLUSION

The results of this investigation suggest that hearing preservation cochlear implantation can be performed either via a round window-related cochleostomy as well as via the round window membrane itself with similar outcomes in terms of both hearing preservation rates as well as speech perception measures.

Electrophysiologic consequences of flexible electrode insertions in gerbils with noise-induced hearing loss

HYPOTHESIS

Flexible electrode interaction with intracochlear structures in a noise-damaged region of the cochlea can lead to measureable electrophysiologic changes.

BACKGROUND

An emerging goal in cochlear implantation is preservation of residual hearing subsequently allowing for combined electric and acoustic stimulation (EAS). However, residual hearing is at least partially lost in most patients as a result of electrode insertion. A gerbil model was used to examine changes to acoustically evoked cochlear potentials during simulated cochlear implantation.

METHODS

Gerbils were partially deafened by noise exposure to mimic residual hearing in human cochlear implant candidates. After 1 month, round window and intracochlear recordings during flexible electrode insertion were made in response to 1 kHz tone burst stimuli at 80 dB SPL. After the insertion, the cochleas were histologically examined for hair cell loss because of the noise exposure and trauma because of the electrode insertion.

RESULTS

Anatomic damage from the flexible electrode was not observable in most cases. However, insertions caused response declines that were, on average, greater than the controls, although some losses were similar to the controls. The CM was more sensitive than the CAP for detecting cochlear disturbance.

CONCLUSION

Because response reductions occurred in the absence of anatomic damage, disturbances in the fluid at the base appear to affect responses from the apex. The losses were less than in previous experiments where the basilar membrane was penetrated.

Cochlear implantation in adults with asymmetric hearing loss

OBJECTIVE

Bilateral severe to profound sensorineural hearing loss is a standard criterion for cochlear implantation. Increasingly, patients are implanted in one ear and continue to use a hearing aid in the nonimplanted ear to improve abilities such as sound localization and speech understanding in noise. Patients with severe to profound hearing loss in one ear and a more moderate hearing loss in the other ear (i.e., asymmetric hearing) are not typically considered candidates for cochlear implantation. Amplification in the poorer ear is often unsuccessful because of limited benefit, restricting the patient to unilateral listening from the better ear alone. The purpose of this study was to determine whether patients with asymmetric hearing loss could benefit from cochlear implantation in the poorer ear with continued use of a hearing aid in the better ear.

DESIGN

Ten adults with asymmetric hearing between ears participated. In the poorer ear, all participants met cochlear implant candidacy guidelines; seven had postlingual onset, and three had pre/perilingual onset of severe to profound hearing loss. All had open-set speech recognition in the better-hearing ear. Assessment measures included word and sentence recognition in quiet, sentence recognition in fixed noise (four-talker babble) and in diffuse restaurant noise using an adaptive procedure, localization of word stimuli, and a hearing handicap scale. Participants were evaluated preimplant with hearing aids and postimplant with the implant alone, the hearing aid alone in the better ear, and bimodally (the implant and hearing aid in combination). Postlingual participants were evaluated at 6 mo postimplant, and pre/perilingual participants were evaluated at 6 and 12 mo postimplant. Data analysis compared the following results: (1) the poorer-hearing ear preimplant (with hearing aid) and postimplant (with cochlear implant); (2) the device(s) used for everyday listening pre- and postimplant; and (3) the hearing aid-alone and bimodal listening conditions postimplant.

RESULTS

The postlingual participants showed significant improvements in speech recognition after 6 mo cochlear implant use in the poorer ear. Five postlingual participants had a bimodal advantage over the hearing aid-alone condition on at least one test measure. On average, the postlingual participants had significantly improved localization with bimodal input compared with the hearing aid-alone. Only one pre/perilingual participant had open-set speech recognition with the cochlear implant. This participant had better hearing than the other two pre/perilingual participants in both the poorer and better ear. Localization abilities were not significantly different between the bimodal and hearing aid-alone conditions for the pre/perilingual participants. Mean hearing handicap ratings improved postimplant for all participants indicating perceived benefit in everyday life with the addition of the cochlear implant.

CONCLUSIONS

Patients with asymmetric hearing loss who are not typical cochlear implant candidates can benefit from using a cochlear implant in the poorer ear with continued use of a hearing aid in the better ear. For this group of 10, the 7 postlingually deafened participants showed greater benefits with the cochlear implant than the pre/perilingual participants; however, further study is needed to determine maximum benefit for those with early onset of hearing loss.

Spread of excitation and channel interaction in single- and dual-electrode cochlear implant stimulation

OBJECTIVES

To determine how simultaneous dual-electrode stimulation (DES) can be optimized for the individual patient to deliver better sound quality and speech recognition. DES was compared with single-electrode stimulation (SES) with respect to the site of stimulation (X) in the cochlea, the spread of excitation (SOE), and channel interaction. Second, it was investigated whether the number of intermediate pitches created with DES can be predicted from SOE, channel interaction measures, current distribution in the cochlea, or distance of the electrode to the medial wall.

DESIGN

Twelve users of the HiRes90K cochlear implant with HiFocus1J electrode were randomly selected to participate in this study. Electrode contacts were selected based on their location in the cochlea as determined by multislice computed tomography, viz. 120 degrees (basal), 240 degrees (middle), and 360 degrees (apical) from the round window. The number of intermediate pitches with simultaneous DES was assessed with a three-alternative forced choice pitch discrimination experiment. The channel interactions between two single-electrode contacts and two DES pairs were determined with a threshold detection experiment (three-alternative forced choice). The eCAP-based SOE method with fixed probe and variable masker was used to determine the location of the neurons responding to a single-electrode contact or dual-electrode contact stimulus. Furthermore, the intracochlear electrical fields were determined with the Electrical Field Imaging tool kit.

RESULTS

DES was not different from SES in terms of channel interaction and SOE. The X of DES was 0.54 electrode contacts more basal compared with SES stimulation, which was not different from the predicted shift of 0.5. SOE and current distribution were significantly different for the three locations in the cochlea but showed no correlation with the number of perceivable pitches. A correlation was found between channel interaction and the number of intermediate pitches along the array within a patient, not between patients.

CONCLUSION

SES and DES are equivalent with regard to SOE and channel interaction. The excitation site of DES has the predicted displacement compared with the excitation region induced by the neighboring single-electrode contact. Unfortunately, no predictor for the number of intermediate pitches was found.

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.

Accuracy of computed tomography detection of superior canal dehiscence

HYPOTHESIS

High-resolution temporal bone computed tomography (CT) may erroneously demonstrate a superior semicircular canal dehiscence (SSCD) where none exists and inaccurately display the size of a dehiscence.

BACKGROUND

CT is an integral component of the diagnosis of SSCD. The prevalence of dehiscence as measured on computed tomographic scan is approximately eightfold higher than that on histologic studies, suggesting that CT may have a relatively low specificity for identifying canal dehiscence. This, in turn, can lead to an inappropriate diagnosis and treatment plan.

METHODS

We quantified the accuracy of CT in identifying a dehiscence of the superior semicircular canal in a cadaver model using microCT as a gold standard. The superior canals of 11 cadaver heads were blue lined. Twelve of the 22 ears were further drilled to create fenestrations of varying sizes. Heads were imaged using medical CT, followed by microCT scans of the temporal bones at 18-µm resolution. Diagnosis of dehiscence and measurements of dehiscence size were performed on clinical CT and compared with that of microCT.

RESULTS

Clinical CT identified 7 of 8 intact canals as dehiscent and tended to overestimate the size of smaller fenestrations, particularly those surrounded by thin bone.

CONCLUSION

These findings confirm that medical CT cannot be used as the exclusive gold standard for SSCD and that, particularly for small dehiscences on CT, clinical symptoms must be clearly indicative of a dehiscence before surgical treatment is undertaken. Preoperative counseling for small dehiscences may need to include the possibility that no dehiscence may be found despite radiologic evidence for it.

Verification of computed tomographic estimates of cochlear implant array position: a micro-CT and histologic analysis

OBJECTIVE

To determine the efficacy of clinical computed tomographic (CT) imaging to verify postoperative electrode array placement in cochlear implant (CI) patients.

STUDY DESIGN

Nine fresh cadaver heads underwent clinical CT scanning, followed by bilateral CI insertion and postoperative clinical CT scanning. Temporal bones were removed, trimmed, and scanned using micro-CT. Specimens were then dehydrated, embedded in either methyl methacrylate or LR White resin, and sectioned with a diamond wafering saw. Histology sections were examined by 3 blinded observers to determine the position of individual electrodes relative to soft tissue structures within the cochlea. Electrodes were judged to be within the scala tympani, scala vestibuli, or in an intermediate position between scalae.

RESULTS

The position of the array could be estimated accurately from clinical CT scans in all specimens using micro-CT and histology as a criterion standard. Verification using micro-CT yielded 97% agreement, and histologic analysis revealed 95% agreement with clinical CT results.

CONCLUSION

A composite, 3-dimensional image derived from a patient's preoperative and postoperative CT images using a clinical scanner accurately estimates the position of the electrode array as determined by micro-CT imaging and histologic analyses. Information obtained using the CT method provides valuable insight into numerous variables of interest to patient performance such as surgical technique, array design, and processor programming and troubleshooting.

Implications of minimizing trauma during conventional cochlear implantation

OBJECTIVE

To describe the relationship between implantation-associated trauma and postoperative speech perception scores among adult and pediatric patients undergoing cochlear implantation using conventional length electrodes and minimally traumatic surgical techniques.

STUDY DESIGN

Retrospective chart review (2002-2010).

SETTING

Tertiary academic referral center.

PATIENTS

All subjects with significant preoperative low-frequency hearing (≤70 dB HL at 250 Hz) who underwent cochlear implantation with a newer generation implant electrode (Nucleus Contour Advance, Advanced Bionics HR90K [1J and Helix], and Med El Sonata standard H array) were reviewed.

INTERVENTION(S)

Preimplant and postimplant audiometric thresholds and speech recognition scores were recorded using the electronic medical record.

MAIN OUTCOME MEASURE(S)

Postimplantation pure tone threshold shifts were used as a surrogate measure for extent of intracochlear injury and correlated with postoperative speech perception scores.

RESULTS

: Between 2002 and 2010, 703 cochlear implant (CI) operations were performed. Data from 126 implants were included in the analysis. The mean preoperative low-frequency pure-tone average was 55.4 dB HL. Hearing preservation was observed in 55% of patients. Patients with hearing preservation were found to have significantly higher postoperative speech perception performance in the CI-only condition than those who lost all residual hearing.

CONCLUSION

Conservation of acoustic hearing after conventional length cochlear implantation is unpredictable but remains a realistic goal. The combination of improved technology and refined surgical technique may allow for conservation of some residual hearing in more than 50% of patients. Germane to the conventional length CI recipient with substantial hearing loss, minimizing trauma allows for improved speech perception in the electric condition. These findings support the use of minimally traumatic techniques in all CI recipients, even those destined for electric-only stimulation.

Assessment of electrode placement and audiological outcomes in bilateral cochlear implantation

OBJECTIVE

The goal of this study was to use highly accurate nonrigid algorithms to locate the position of cochlear implant (CI) electrodes and correlate this with audiological performance.

PATIENTS

After obtaining institutional review board approval, adult patients who had bilateral CIs were identified, and those with preoperative temporal bone computed tomographic scans were asked to return for a postintervention computed tomography. Sixteen adult patients agreed. Demographics, cause of deafness, length of auditory deprivation, and audiological performance were recorded.

INTERVENTION

Using a nonrigid model of the shape variations of intracochlear anatomy, the location of the basilar membrane was specified in relationship to the electrode array. The number of electrodes within each compartment of the cochlea was correlated with hearing in noise and consonant-noun-consonant scores for the known confounding variable: length of deafness.

MAIN OUTCOMES

Mann-Whitney U tests of differences were used to compare the hearing performance resulting from implants completely in the scala tympani (ST) versus those not completely in the ST.

RESULTS

Of all implants, 62.5% were fully inserted in the ST; 34.4% were partially inserted into the ST and 3.1% was fully inserted in the scala vestibuli. Controlling for the known contributing variable of length of auditory deprivation, our results show that the location of electrodes in relationship to the scala is not predictive of audiological performance.

CONCLUSION

We have assessed electrode placement and correlated it with audiological outcome. The presence of the electrodes solely in the ST was not predictive of outcome. We estimate that it would take analyzing data of thousands of CI patients before any valid correlations can be made.