• Tobias Butzer, Eirik Juelke, Abraam Yacoub, Wilhelm Wimmer, Marco Caversaccio, and Lukas Anschuetz.
• Department of Otolaryngology Head and Neck Surgery, Inselspital University Hospital and University of Bern, Bern, Switzerland; Hearing Research Laboratory, ARTORG Center for Biomedical Engineering, University of Bern, Bern, Switzerland. Electronic address: tobias.buetzer@unibe.ch.
• World Neurosurg. 2022 Apr 1; 160: e88-e95.

ObjectiveMinimally invasive transcanal transpromontorial endoscopic approaches to the internal auditory canal sacrifice the cochlea. Two hearing-preserving approaches, the exclusively endoscopic transcanal infracochlear approach and the endoscope-assisted transmastoid retrolabyrinthine approach, have been controversially discussed in the literature. In this study, we examine the feasibility of these 2 approaches by means of three-dimensional surface models, a population-based analysis of the available surgical space, and dissections in human whole-head specimens.MethodsWe reconstructed three-dimensional surface models based on clinical high-resolution computed tomography scans of 53 adult temporal bones. For both approaches, we measured the maximal extensions and the area of the surgical access windows located between landmarks on the surrounding anatomic structures. We then identified the limiting extensions and derived the cumulative distribution to describe the available surgical space. Dissections were performed to validate the corridors and landmark selection.ResultsThe limiting extension for the infrachochlear approach is 7.0 ± 2.7 mm from the round window to the dome of the jugular bulb. The limiting extension for the retrolabyrinthine approach is 6.4 ± 1.5 mm from the dura of the posterior fossa to the facial nerve. The cumulative distribution shows that 80% of the cohort have access window extensions ≥3 mm for both approaches.ConclusionsThis study shows that in a high percentage of the measured cohort, the access windows are sufficiently large for endoscopic approaches to the internal auditory canal. With appropriate instrumentation, these hearing-preserving minimally invasive approaches may evolve into alternatives to surgical treatment.Copyright © 2021 The Author(s). Published by Elsevier Inc. All rights reserved.

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