Objectives: Candidacy for cochlear implantation (CI) has expanded over the years, including individuals with inner ear malformations (IEMs). Individuals with IEMs are likely to present aberrant distribution of the auditory nerve and a low survival rate of the spiral ganglion neurons. The health of the auditory nerve of individuals with the IEMs may play an important role in determining CI outcomes compared to those with the normal cochlea. This study aimed to characterize the influence of IEMs on intraoperative electrically-evoked compound action potential (ECAP) and auditory performance to understand underlying pathophysiology related to variabilities in CI outcomes that individuals with malformed cochlea may present.
Methods: This retrospective study reviewed the medical records of 222 ears implanted with Cochlear Nucleus CI. Subjects were grouped based on imaging study results. 64 ears had radiologic evidence of IEMs; 38 had mild IEMs (e.g., enlarged vestibular aqueduct, incomplete partition type II, etc.) and 26 had severe IEMs (e.g., common cavity, cochlear nerve hypoplasia/aplasia etc.). 158 ears had normal cochlear structures and intact auditory nerve. Intraoperative ECAP thresholds obtained via neural response telemetry (NRT) and the categories of auditory performance (CAP) scores measured at postop 12 months were compared and correlated.
Results: Absent NRT responses were more apparent in the IEM group. Average NRT thresholds were significantly higher in the IEM group compared to the normal group. When two IEM subgroups were compared, the severe IEM group showed highly elevated NRT thresholds, while the mild IEM group had NRT thresholds comparable to the normal group. The mild IEM group was able to achieve CAP scores similar to the normal group. In contrast, the severe IEM group showed considerably lower CAP scores even 12 months after CI. A moderate but significant negative relationship existed between NRT thresholds and CAP scores, indicating subjects who had lower NRT thresholds tended to achieve higher CAP scores.
Conclusion: Measurable ECAP responses and average ECAP thresholds were varied among groups. The inverse relationship between NRT thresholds and CAP scores may suggest that electrophysiological responses measured during the surgery may be indicative of estimating postoperative auditory performance in our CI population.

**Objectives:** Candidacy for cochlear implantation (CI) has expanded over the years, including individuals with inner ear malformations (IEMs). Individuals with IEMs are likely to present aberrant distribution of the auditory nerve and a low survival rate of the spiral ganglion neurons. The health of the auditory nerve of individuals with the IEMs may play an important role in determining CI outcomes compared to those with the normal cochlea. This study aimed to characterize the influence of IEMs on intraoperative electrically-evoked compound action potential (ECAP) and auditory performance to understand underlying pathophysiology related to variabilities in CI outcomes that individuals with malformed cochlea may present.
**Methods:** This retrospective study reviewed the medical records of 222 ears implanted with Cochlear Nucleus CI. Subjects were grouped based on imaging study results. 64 ears had radiologic evidence of IEMs; 38 had mild IEMs (e.g., enlarged vestibular aqueduct, incomplete partition type II, etc.) and 26 had severe IEMs (e.g., common cavity, cochlear nerve hypoplasia/aplasia etc.). 158 ears had normal cochlear structures and intact auditory nerve. Intraoperative ECAP thresholds obtained via neural response telemetry (NRT) and the categories of auditory performance (CAP) scores measured at postop 12 months were compared and correlated.
**Results:** Absent NRT responses were more apparent in the IEM group. Average NRT thresholds were significantly higher in the IEM group compared to the normal group. When two IEM subgroups were compared, the severe IEM group showed highly elevated NRT thresholds, while the mild IEM group had NRT thresholds comparable to the normal group. The mild IEM group was able to achieve CAP scores similar to the normal group. In contrast, the severe IEM group showed considerably lower CAP scores even 12 months after CI. A moderate but significant negative relationship existed between NRT thresholds and CAP scores, indicating subjects who had lower NRT thresholds tended to achieve higher CAP scores.
**Conclusion:** Measurable ECAP responses and average ECAP thresholds were varied among groups. The inverse relationship between NRT thresholds and CAP scores may suggest that electrophysiological responses measured during the surgery may be indicative of estimating postoperative auditory performance in our CI population.

Effect of inner ear malformations on intraoperative electrically evoked compound action potential (ECAP) thresholds and postoperative auditory performance

It is with great pleasure and enthusiasm, that on behalf of the Cochlear Implant centers of the Radboud UMC in Nijmegen and Erasmus MC Sophia Children’s Hospital in Rotterdam to invite you to attend the 16th European Symposium on Pediatric Cochlear Implantation to Rotterdam, the Netherlands in 2023.

Yours sincerely, on behalf of the CI Centers at Radboud UMC and Erasmus MC,