High-frequency Cochlear Nerve Deficit Region: Relationship With Deaf Duration and Cochlear Implantation Performance in Postlingual Deaf Adults

Cortical volumetric changes after cochlear implantation in postlingually deaf adults: correlation with speech perception abilities

This study aims to analyse the volumetric changes in brain MRI after cochlear implantation (CI), focusing on the speech perception in postlingually deaf adults. We conducted a prospective cohort study with 16 patients who had bilateral hearing loss and received unilateral CI. Based on the surgical side, patients were categorized into left and right CI groups. Volumetric T1-weighted brain MRI were obtained before and one year after the surgery. To overcome the artifact caused by the internal device in post-CI scan, image reconstruction method was newly devised and applied using the contralateral hemisphere of the pre-CI MRI data, to run FreeSurfer. We conducted within-subject template estimation for unbiased longitudinal image analysis, based on the linear mixed effect models. When analyzing the contralateral cerebral hemisphere before and after CI, a substantial increase in superior frontal gyrus and superior temporal gyrus (STG) volumes was observed in the left CI group. A positive correlation was observed in the STG and post-CI word recognition score in both groups. As far as we know, this is the first study attempting longitudinal brain volumetry based on post-CI MRI scans. We demonstrate that better auditory performance after CI is associated with structural restoration in central auditory structures.

Anatomical Features of Children With Mondini Dysplasia: Influence on Cochlear Implantation Performance

OBJECTIVE

To analyze the long-term auditory performance after cochlear implantation (CI) and identify anatomical features of Mondini dysplasia associated with post-CI outcomes.

STUDY DESIGN

Retrospective study.

SETTING

Tertiary care academic center.

PATIENTS

We enrolled 49 ears with Mondini dysplasia who underwent CI with more than 7 years of follow-up and age at CI- and sex-matched control group with radiologically normal inner ears.

MAIN OUTCOMES AND MEASURES

The development of auditory skills after CI was evaluated using word recognition scores (WRSs). The anatomical features were measured based on temporal bone computed tomography and magnetic resonance imaging, involving the width of the bony cochlear nerve canal (BCNC), cochlear basal turn, enlarged vestibular aqueduct, cochlear height, and diameter of the cochlear nerve (CN).

RESULTS

CI in ears with Mondini dysplasia showed comparable benefits and improvement of auditory performance to controls during the 7 years of follow-up. In Mondini dysplasia, four (8.2%) ears showed narrow BCNC (<1.4 mm) with poorer WRS (58 ± 17%) than those with normal-sized BCNC, which had WRS (79 ± 10%) comparable to that of the control group (77 ± 14%). In Mondini dysplasia, the maximum ( r = 0.513, p < 0.001) and minimum ( r = 0.328, p = 0.021) CN diameters had positive correlations with post-CI WRS. The maximum CN diameter ( β = 48.347, p < 0.001) and BCNC width ( β = 12.411, p = 0.041) were significant factors that influence the post-CI WRS in multiple regression analysis.

CONCLUSIONS

Preoperative anatomical evaluation, especially BCNC status and CN integrity, may serve as predictive markers for post-CI performance.

The Acoustic Change Complex in Response to Frequency Changes and Its Correlation to Cochlear Implant Speech Outcomes

One of the biggest challenges that face cochlear implant (CI) users is the highly variable hearing outcomes of implantation across patients. Since speech perception requires the detection of various dynamic changes in acoustic features (e.g., frequency, intensity, timing) in speech sounds, it is critical to examine the ability to detect the within-stimulus acoustic changes in CI users. The primary objective of this study was to examine the auditory event-related potential (ERP) evoked by the within-stimulus frequency changes (F-changes), one type of the acoustic change complex (ACC), in adult CI users, and its correlation to speech outcomes. Twenty-one adult CI users (29 individual CI ears) were tested with psychoacoustic frequency change detection tasks, speech tests including the Consonant-Nucleus-Consonant (CNC) word recognition, Arizona Biomedical Sentence Recognition in quiet and noise (AzBio-Q and AzBio-N), and the Digit-in-Noise (DIN) tests, and electroencephalographic (EEG) recordings. The stimuli for the psychoacoustic tests and EEG recordings were pure tones at three different base frequencies (0.25, 1, and 4 kHz) that contained a F-change at the midpoint of the tone. Results showed that the frequency change detection threshold (FCDT), ACC N1' latency, and P2' latency did not differ across frequencies (p > 0.05). ACC N1'-P2 amplitude was significantly larger for 0.25 kHz than for other base frequencies (p < 0.05). The mean N1' latency across three base frequencies was negatively correlated with CNC word recognition (r = -0.40, p < 0.05) and CNC phoneme (r = -0.40, p < 0.05), and positively correlated with mean FCDT (r = 0.46, p < 0.05). The P2' latency was positively correlated with DIN (r = 0.47, p < 0.05) and mean FCDT (r = 0.47, p < 0.05). There was no statistically significant correlation between N1'-P2' amplitude and speech outcomes (all ps > 0.05). Results of this study indicated that variability in CI speech outcomes assessed with the CNC, AzBio-Q, and DIN tests can be partially explained (approximately 16-21%) by the variability of cortical sensory encoding of F-changes reflected by the ACC.