Analysis of Cochlear Morphology for Cochlear Implantation Using Three-Dimensional Reconstruction of Computed Tomography Images

Abstract

Plain Language SummarySubjects suffering from sensorineural deafness have been able to regain partial hearing and speech understanding using cochlear implants. The frequency mapping of the cochlea is important for postoperative success. However, the frequency distribution of the human cochlea varies among individuals due to variations in cochlear length. Accurate measures of cochlear duct length for preoperatively defining this length are needed to maximize the effect of frequency mapping. This study analyzed the length and shape of the cochlea using three-dimensional reconstructions of the temporal bone based on computed tomography scans. Eight angular points (P0–P7) every 90° were selected from 0° to 630° from the center of the round window using the reconstructed cochlear canal images. The radius (R) and thickness (T) of the cochlear canal at each point were measured. Each point was theoretically positioned 90° relative to the origin starting from the center of the round window. Therefore, P0 and P7 are the angular points at 0° and 630°, respectively. The coiling ratio of the cochlea was measured using the ratios R4/R0, R5/R1, R6/R2, and R7/R3. The cochlear canal length (CoCL) was estimated using an equation based on the radius at each point. The mean CoCL from 0° to 630° was 31.5 mm, and the cochlear volume was 55.9 mm3. Based on the Greenwood and Erixon equations, our CoCL 360° and 630° measurements corresponded to frequencies of 982 (759–1,405) Hz and 312 (158–499) Hz. These are comparable with previously reported values.