Anatomical investigation of safe trajectory determining factors in robotic cochlear implant surgery with computed tomography images

The ideal trajectory to insert a cochlear implant array is defined by an entrance through the round window membrane and continues as long as possible parallel to the basal turn of the cochlea. Facial recess width and angle, canonus thickness, round window sizes, and cochlear orientation are important for determining the safe trajectory in both robot-assisted and conventional cochlear implantation surgery. In addition, it is thought that there may be a significant relationship between the postoperative electrode insertion depth degree and cochlear orientation. Here in this, thesis we examined the keyhole drilling trajectories of cochlear implantation surgeries performed with the HEARO Procedure to compare the critical anatomical structures between easy and difficult cases. Preoperative and postoperative computed tomography images of patients who underwent robot-assisted and conventional cochlear implant surgery at UZ Brussel Hospital were included in the study. Radiological images in DICOM format were transferred to a dedicated software for analyses. OTOPLAN, (CASCINATION AG, Bern, Switzerland) was used for 3D reconstruction of the temporal bone, auditory ossicles, facial nerve, chorda tympani, cochlea, and round window. In addition, depth of the facial nerve, facial recess angle, and cochlear orientation angles were measured with RadiAnt DICOM Viewer. Facial recess width, facial recess angle, and distance between the facial nerve and safe trajectory were statistically smaller in patients whose safe distance to the facial nerve could not be guaranteed with intraoperative imaging. A significant positive correlation existed between basal turn angle and in-plane angle. The facial recess anatomy was the most critical factor for safe robotic inner ear access in our series here. Additionally, insight on the cochlear orientation before robotic surgery helps ensure a collision-free trajectory and feasible (safer) approach angles to the cochlea. In both robotic and conventional surgery, preoperative assessment of cochlear dimensions is crucial for appropriate electrode selection and, consequently, for postoperative audiological outcomes. The findings of this study are considered to be a reference for future studies in achieving collision-free trajectory planning in robotic-assisted cochlear implant surgery.