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Cochlear implants (CIs) are neural prosthetics which use an array of implanted electrodes to improve hearing in patients with severe-to-profound hearing loss. After implantation, the CI is programmed by audiologists who adjust various parameters to optimize hearing performance for the patient. Without knowing which auditory nerve fibers (ANFs) are being stimulated by each electrode, this process can require dozens of programming sessions and often does not lead to optimal programming. The internal auditory canal (IAC) houses the ANFs as they travel from the implantation site, the cochlea, to the brain. In this paper, we present a method for localizing the IAC in a CT image by deforming an atlas IAC mesh to a CT image using a 3D U-Net. Our results suggest this method is more accurate than an active shape model-based method when tested on a test set of 20 images with ground truth. This IAC segmentation can be used to infer the position of the invisible ANFs to assist with patient-specific CI programming.

Hypothesis Angled endoscopes have been postulated to increase visualization of the internal auditory canal (IAC); however, few studies have quantified the extent of IAC visualization using endoscopes of varying angles. Background Preservation of the bony labyrinth in middle fossa (MF) vestibular schwannoma surgery may limit visualization of the lateral IAC. We sought to determine the extent to which IAC visualization is increased with endoscopes in these situations. Methods Computed tomography (CT) scans were acquired before and after two cadaveric MF bony drill-outs. An atlas-based method was used to localize the IAC in the preprocedure CT and then registered with the postprocedure CT using standard image registration methods. Virtual microscope and endoscope positions and angles of approach were determined in a 3D rendering environment. Using ray casting techniques, the percentage of IAC surface area visible (unobscured by bony structures) with the microscope and 0°, 30°, and 45° endoscopes was calculated. Results For cadaver 1, the microscope led to visible IAC surface areas of 72%, whereas 0°, 30°, and 45° endoscopes visualized 58%, 79%, and 84%, respectively. For cadaver 2, the microscope led to visible surface areas of 67%, whereas the same endoscopes visualized 66%, 84%, and 84%, respectively. Conclusions Using a microscope yields similar proportions of visible IAC surface area to a 0° endoscope in MF bony drill-outs. Increased visualization of the IAC is possible with more angled endoscopes. Using angled endoscopes may facilitate improved tumor dissection in the lateral IAC with neural and vascular preservation in vestibular schwannoma surgery aimed at hearing preservation.