2023 Volume 33 Issue 3 Pages 170-174
Among recently developed electrode arrays, slim modiolar electrode arrays are prone to folding within the cochlea, a condition known as tip fold-over. One of the mechanisms that cause tip fold-over is the misalignment between the electrode array’s coiling direction and the cochlea’s curving direction. Thus, surgeons should be careful during slim modiolar electrode insertion and align the coiling planes of the electrode array and the cochlea. However, successful alignment of the electrode array’s coiling direction and the cochlea’s curving direction largely depends on the surgeon’s imagination. We recommended preoperative three-dimensional simulation to determine the correct coiling plane of the cochlea. However, not all surgeons are familiar with preoperative simulations using computers. Therefore, we developed a method of determining the coiling plane of the cochlea using anatomical landmarks that can be visualized during cochlear implantation.
We retrospectively investigated preoperative CT data of 65 ears of patients who underwent cochlear implantation by one surgeon during the period of 2017–2021. Revision cases and inner ear anomaly cases were excluded. The preoperative CT dataset was three-dimensionally reconstructed. A plane was defined containing short and long processes of the incus, as “plane of the incus”. The angle between the plane of the incus and the coiling plane of the cochlea (incudocochlear angle) were measured and collected. The incudocochlear angle was averaged at 34.6 degrees. No statistical differences were noted between the left and right ears. No statistical differences were noted in terms of age at surgery. The 95% confidence interval of the angle was 23.4–45.7 degrees. Thus, once the incus is visualized during surgery, it is possible to correctly determine the coiling plane of the cochlea. This simple method does not require the surgeon’s ability of computer simulation and may help prevent misalignment and subsequent electrode tip fold-over.
