Consequences for CI length selection derived from the preoperative human cochlear duct length estimation and frequency map modeling

Ever since the cochlear implant (CI) was first introduced, efforts were made to improve hearing outcome in patients. Matching the individual patients’ needs and anatomical properties with the CIs’ frequency map and constructional properties is a promising approach to achieve this goal. With recent improvements in preoperative diagnostics with computed tomography and the availability of CI electrodes in different lengths, it became more feasible than ever. Also, as the indication of CI-applications is further expanding, for example an increasing number of implanted patients with residual hearing in the low frequency range is approached.

The length along the organ of Corti (CDL OC) was reported to have great inter- individual variability between 24 and 36 mm. This emphasizes the need of preoperative length estimation. The A-value (longest distance between the round window and the opposite cochlear wall in the basal turn) has been suggested to serve this purpose. To validate this for our CI candidate population CT and MR images of several hundred Tübingen CI-patients were retrospectively evaluated to determine the A-value and the 3D-length measured CDL along the of the lateral wall (LW). The A-value ranged between 8 and 10 mm, the CDL-LW valued between 31 and 44 mm. These two measured correlated significantly well. Therefore, the A-value serves the purpose described above. To match the patients’ and the CIs’ frequency map, the CDL-LW was modeled based on a logarithmic spiral and the tonotopical position was calculated based on Greenwood, Schuknecht and pitch-matching data.

Poster-PDF A-1845.PDF

Publication History

Article published online:
10 June 2020