Correlation Between Cochlear Length, Insertion Angle, and Tonotopic Mismatch for MED-EL FLEX28 Electrode Arrays

Area of Science:

• Otoacoustic Emissions
• Auditory Neuroscience
• Medical Imaging

Background:

• Tonotopic organization maps sound frequency to specific locations in the cochlea.
• Cochlear implantation aims to restore hearing by stimulating these tonotopic locations.
• Discrepancies between electrode placement and tonotopic maps (tonotopic mismatch) can affect hearing outcomes.

Purpose of the Study:

• To investigate the relationship between cochlear length, electrode insertion angle, and tonotopic mismatch.
• To compare tonotopic mismatch relative to the spiral ganglion versus the organ of Corti.

Main Methods:

• Retrospective analysis of computed tomography (CT) images from 106 patients undergoing cochlear implantation.
• Assessment of cochlear length, insertion angle, and depth using OTOPLAN software.
• Estimation and comparison of tonotopic mismatch using Greenwood (organ of Corti) and Stakhovskaya (spiral ganglion) maps.

Main Results:

• Cochlear length was negatively correlated with insertion angle (p < 0.004).
• Tonotopic mismatch was greater at the organ of Corti than the spiral ganglion.
• Larger cochleae and apical regions showed greater tonotopic mismatch at the organ of Corti.

Conclusions:

• Smaller cochlear size was associated with a higher insertion angle and reduced tonotopic mismatch.
• Preoperative selection of electrode arrays based on cochlear morphology and postoperative frequency fitting can minimize tonotopic mismatch.