Effect of Insertion Depth on Hearing Preservation after CI: Indication for Electric or Electric-Acoustic Stimulation

Introduction:

Preserving residual hearing in cochlear implantation (CI) is mostly achieved by reducing the electrode carriers length. The goal of this study was to find individually appropriate insertion depth either for combined electric-acoustic stimulation (EAS) or for only electric stimulation (ES), and thus find better indication boundaries.

Methods:

91 patients were retrospectively included in this study. They received free-fitting electrodes with lengths of 20 (n = 7), 24 (n = 28), 28 (n = 32) and 31.5 mm (n = 24). All patients had preoperative residual hearing < 1 kHz and no long-term deafness. For each treated ear, the angle of insertion was estimated using postoperative x-ray imaging. Audiometric tests were conducted for given time intervals (pre- and postoperative, 6 and 12 months after CI).

Results:

Two normally distributed angle-of-insertion groups were found in our data: one group with shallow insertion (SI) and one with deep insertion (DI). Preoperatively, the SI group showed significantly better speech test scores as expected. In contrast, the DI group showed better scores in the postoperative time interval. At 6 and 12 months after CI, no significant differences were found. Still, when EAS and ES users were compared, EAS users showed significantly better scores. For ES, a positive correlation (r = 0.29) between speech test scores and the angle of insertion was observed. Refined indication boundaries for EAS or ES users will be suggested based on these data.

Conclusion:

Patients who are ES users can benefit from deeper insertion, however, EAS users still demonstrate better speech outcomes and thus advocate shallower insertion. Therefore, individual consideration of patients remains an important criterion.

Publication History

Publication Date:
18 April 2018 (online)