Objective: To evaluate the relationship between intrascalar electrode location, electrode type (lateral wall, perimodiolar, and midscala), and angular insertion depth on residual hearing in cochlear implant (CI) recipients.
Setting: Tertiary academic hospital.
Patients: Adult CI patients with functional preoperative residual hearing with preoperative and postoperative CT scans.
Intervention: Audiological assessment after CI.
Main outcome measures: Electrode location, angular insertion depth, residual hearing post-CI, and word scores with CI (consonant-nucleus-consonant [CNC]).
Results: Forty-five implants in 36 patients (9 bilateral) were studied. Thirty-eight electrode arrays (84.4%) were fully inserted in scala tympani (ST), 6 (13.3%) crossed from ST to scala vestibuli (SV), and 1 (2.2%) was completely in SV. Twenty-two of the 38 (57.9%) with full ST insertion maintained residual hearing at 1 month compared with 0 of the 7 (0%) with non-full ST insertion (p = 0.005). Three surgical approaches were used: cochleostomy (C) 6/44, extended round window (ERW) 8/44, and round window (RW) 30/44. C and ERW were small group to compare with RW approaches. However if we combine C + ERW, then RW has higher chance of full ST insertion (p = 0.014). Looking at the full ST group, neither age, sex, nor electrode type demonstrated statistically significant associations with hearing preservation (p = 0.646, p = 0.4, and p = 0.929, respectively). The median angular insertion depth was 429° (range, 373°-512°) with no significant difference between the hearing and nonhearing preserved groups (p = 0.287).
Conclusion: Scalar excursion is a strong predictor of losing residual hearing. However, neither age, sex, electrode type, nor angular insertion depth was correlated with hearing preservation in the full ST group. Techniques to decrease the risk of electrode excursion from ST are likely to result in improved residual hearing and CI performance.