The Dependency of Cochlear Lateral Wall Measurements on Observer and Imaging Type

Abstract

Hypothesis Assessment techniques for the cochlear spatial lateral wall are associated with inter-rater variability, but derived clinical recommendations nonetheless offer value for individualized electrode selection. Background Anatomical variations influence the location of cochlear implant electrodes inside the cochlea. Preoperative planning allows individualization of the electrode based on characterization of the bony lateral wall. Methods The study used publicly available digitized temporal bones based on microslicing and computed tomography. Four experienced observers assessed the lateral wall applying manual tracing, linear regression scaling and elliptic-circular approximation methods in all modalities. Radial and height differences were computed in 90-degree steps from the round window center to the apex. Total length, total angular length, and tonotopic frequencies were computed for each reconstruction. Results Differences were found most pronounced between assessment methods in vertical direction across observers and imaging modalities. One of the five anatomies was consistently found to be of shorter cochlear duct length with estimation techniques yielding more conservative results compared with manual tracings. Conclusions Assessment techniques for the bony lateral wall yield method, observer, and image modality related deviations. Automation of the anatomical characterization may offer potential in minimizing inaccuracies. Nonetheless, observers were consistently able to detect a smaller inner ear demonstrating the ability of current methods to contribute to an optimized choice of electrodes based on individual patient anatomy.