Objectives: The spatial position of a cochlear implant (CI) electrode array affects the spectral cues provided to the recipient. Differences in cochlear size and array length lead to substantial variability in angular insertion depth (AID) across and within array types. For CI-alone users, the variability in AID results in varying degrees of frequency-to-place mismatch between the default electric frequency filters and cochlear place of stimulation. For electric-acoustic stimulation (EAS) users, default electric frequency filters also vary as a function of residual acoustic hearing in the implanted ear. The present study aimed to (1) investigate variability in AID associated with lateral wall arrays, (2) determine the subsequent frequency-to-place mismatch for CI-alone and EAS users mapped with default frequency filters, and (3) examine the relationship between early speech perception for CI-alone users and two aspects of electrode position: frequency-to-place mismatch and angular separation between neighboring contacts, a metric associated with spectral selectivity at the periphery. Design: One hundred one adult CI recipients (111 ears) with MED-EL Flex24 (24 mm), Flex28 (28 mm), and FlexSOFT/Standard (31.5 mm) arrays underwent postoperative computed tomography to determine AID. A subsequent comparison was made between AID, predicted spiral ganglion place frequencies, and the default frequency filters for CI-alone (n = 84) and EAS users (n = 27). For CI-alone users with complete insertions who listened with maps fit with the default frequency filters (n = 48), frequency-to-place mismatch was quantified at 1500 Hz and angular separation between neighboring contacts was determined for electrodes in the 1 to 2 kHz region. Multiple linear regression was used to examine how frequency-to-place mismatch and angular separation of contacts influence consonant-nucleus-consonant (CNC) scores through 6 months postactivation. Results: For CI recipients with complete insertions (n = 106, 95.5%), the AID (mean ± standard deviation) of the most apical contact was 428° ± 34.3° for Flex24 (n = 11), 558° ± 65.4° for Flex28 (n = 48), and 636° ± 42.9° for FlexSOFT/Standard (n = 47) arrays. For CI-alone users, default frequency filters aligned closely with the spiral ganglion map for deeply inserted lateral wall arrays. For EAS users, default frequency filters produced a range of mismatches; absolute deviations of ≤ 6 semitones occurred in only 37% of cases. Participants with shallow insertions and minimal or no residual hearing experienced the greatest mismatch. For CI-alone users, both smaller frequency-to-place mismatch and greater angular separation between contacts were associated with better CNC scores during the initial 6 months of device use. Conclusions: There is significant variability in frequency-to-place mismatch among CI-alone and EAS users with default frequency filters, even between individuals implanted with the same array. When using default frequency filters, mismatch can be minimized with longer lateral wall arrays and insertion depths that meet the edge frequency associated with residual hearing for CI-alone and EAS users, respectively. Smaller degrees of frequency-to-place mismatch and decreased peripheral masking due to more widely spaced contacts may independently support better speech perception with longer lateral wall arrays in CI-alone users.

Objective: The objective of this study is to determine the reliability of a new tablet-based software that utilizes postoperative computed tomography to determine angular insertion depth (AID), cochlear duct length (CDL), and the cochlear place frequency of individual electrodes in cochlear implant recipients. Patients: Twenty adult cochlear implant recipients with lateral-wall electrode arrays of varying lengths were included in the study. Intervention: Cochlear and electrode array measurements were made by 2 otolaryngologists using a tablet-based software. The user manually identifies the modiolus, round window, and each electrode contact to calculate AID. The user also manually identifies cochlear landmarks to calculate the CDL. The AID and CDL are applied to the Greenwood function to obtain an estimate of the cochlear place frequency for each electrode. Main Outcome Measure(s): The primary outcome measure was the reliability of the instrument, as assessed with intra and interrater reliability of measured AID and CDL. The resultant differences in the estimated cochlear place frequency of the most apical electrode were also evaluated. Results: A broad range of AIDs were observed (390°–659°). Intraclass correlation coefficients for intra (0.991) and interrater reliability (0.980) of AID of the most apical electrode contact were excellent. Intra (0.820) and interrater reliability (0.784) of CDL were also excellent. The estimated cochlear place frequency for the most apical electrode differed by an average of 6.7% (0–18.7%) across the 2 raters. Conclusion: There is excellent agreement amongst clinicians in the determination of AID and CDL, resulting in small changes in estimated cochlear place frequency of the most apical electrode using this new software.

A prospective clinical trial evaluated the effectiveness of cochlear implantation in adults with asymmetric hearing loss (AHL). Twenty subjects with mild-to-moderate hearing loss in the better ear and moderate-to-profound hearing loss in the poorer ear underwent cochlear implantation of the poorer hearing ear. Subjects were evaluated preoperatively and at 1, 3, 6, 9, and 12 months post-activation. Preoperative performance was evaluated unaided, with traditional hearing aids (HAs) or with a bone-conduction HA. Post-activation performance was evaluated with the cochlear implant (CI) alone or in combination with a contralateral HA (bimodal). Test measures included subjective benefit, word recognition, and spatial hearing (i.e., localization and masked sentence recognition). Significant subjective benefit was reported as early as the 1-month interval, indicating better performance with the CI compared with the preferred preoperative condition. Aided word recognition with the CI alone was significantly improved at the 1-month interval compared with preoperative performance with an HA and continued to improve through the 12-month interval. Subjects demonstrated early, significant improvements in the bimodal condition on the spatial hearing tasks compared with baseline preoperative performance tested unaided. The magnitude of the benefit was reduced for subjects with AHL when compared with published data on CI users with normal hearing in the contralateral ear; this finding may reflect significant differences in age at implantation and hearing sensitivity across cohorts.