Cochlear duct length and cochlear distance on preoperative CT: imaging markers for estimating insertion depth angle of cochlear implant electrode

Objectives Preoperative estimation of the insertion depth angle of cochlear implant (CI) electrodes is essential for surgical planning. The purpose of this study was to determine the cochlear size using preoperative CT and to investigate the correlation between cochlear size and insertion depth angle in morphologically normal cochlea. Methods Thirty-five children who underwent CI were included in this study. Cochlear duct length (CDL) and the diameter of the cochlear basal turn (distance A/B) on preoperative CT and the insertion depth angle of the CI electrode on postoperative radiographs were independently measured by two readers. Correlation between cochlear size and insertion depth angle was evaluated. Interobserver agreement was calculated using the intraclass correlation coefficient (ICC). Results The mean CDL, distance A, and distance B of 70 ears were 36.20 ± 1.57 mm, 8.67 ± 0.42 mm, and 5.73 ± 0.32 mm, respectively. The mean insertion depth angle was 431.45 ± 38.42°. Interobserver agreements of CDL, distance A/B, and insertion depth angle were fair to excellent (ICC 0.864, 0.862, 0.529, and 0.958, respectively). Distance A ( r = − 0.7643) and distance B ( r = − 0.7118) showed a negative correlation with insertion depth angle, respectively ( p < 0.0001). However, the correlation between CDL and insertion depth angle was not statistically significant ( r = − 0.2333, p > 0.05). Conclusions The CDL and cochlear distance can be reliably obtained from preoperative CT. Distance A can be used as a predictive marker for estimating insertion depth angle during CI surgery.