Retrospective study: Electrophysiological changes in straight cochlear implant electrodes in association of insertion depth and the cochlear size

Introduction 

Different factors influence the electrophysiological changes after cochlear implant treatment. The threshold values ​​of the electrically evoked compound action potentials (E-CAP) are primarily dependent on the distance between the electrode carrier and the spiral ganglion. Furthermore, the diameter of the cochlea decreases towards the tip. There is thus the hypothesis that the deeper the insertion depth and the larger the cochlea, the lower the ECAP threshold values ​​of the electrode carriers.

Material and Methods 

In a retrospective setting, patients who were implanted unilaterally with a lateral wall electrode between 2011 and 2020 were examined. The intraoperatively measured ECAP threshold values ​​(t-NRT) were compared with the insertions depth of the electrode and the size of the cochlea.

Results 

Between 2011 and 2020, 50 patients were implanted with a lateral wall electrode (Nucleus Slim straight). The mean age of deafness was 63 years, 25 patients were male, 25 female. The apical t-NRT showed lower threshold values ​​than basal. There is a significant correlation between increasing insertions depth and decreasing threshold values. The size of the cochlea has no effect on the thresholds.

Discussion 

In addition to the intracochlear position of the CI electrode, various factors have an influence on the intracochlear electrophysiological parameters. Intracochlear pathologies such as otosclerosis or intracochlear fibrosis lead to different ECAP threshold values. With lateral wall electrodes, the depth of insertion plays a decisive role. The diameter in the apical part of the cochlea is getting smaller and thus the electrode approaches the modiolus. In our work this approximation is reflected in the decrease in the threshold values ​​of the ECAPs.

Publication History

Article published online:
24 May 2022