Scalar localization by computed tomography of cochlear implant electrode carriers designed for deep insertion

This study aimed to evaluate the possibility of predicting radiologically the scalar localization of a 31.5-mm-long, free-fitting electrode carrier for cochlear implantation, using conventional planar computed tomography.

A cross-sectional human temporal bone study was conducted.

Twenty human temporal bones were acquired postmortem and implanted with 31.5-mm-long electrode carriers. Ten of these were implanted into the scala tympani using the round window approach, whereas the other 10 electrodes were inserted into the scala vestibuli by cochleostomy. Computed tomography was then performed, and 2 experienced blinded radiologists evaluated the intracochlear position of the array.

The estimated position of the electrode carrier was described using a 5-point scale. After sectioning and histologic investigation, the results of the radiologic and histologic investigations were compared.

In 17 of 20 cases, it was possible to estimate the correct position of the electrode carrier within the basal turn of the cochlea by means of computed tomography. As the insertion angles widened beyond 360 degrees, it became increasing difficult for the radiologists to correctly determine the position of the electrode carrier.

The comparison of our temporal bone experiment results with the computed tomography results revealed the difficulty of assessing the correct position of intracochlear electrodes. Scalar localization of deeply inserted electrode carriers cannot be precisely determined by means of computed tomography.