Radiomorphometric Comparison of Endoscopic Presigmoid Hearing-Preserving Approaches to The Internal Auditory Canal

Background: The retrolabyrinthine (RL) approach provides hearing-preserving exposure to the internal auditory canal (IAC), though its limited exposure of the lateral IAC has restricted its popularized use in vestibular schwannoma surgery. Use of endoscopic techniques may overcome this limitation. The transcrural (TC) approach offers greater access by partially removing and sealing the labyrinth. We compared post-dissection accessible IAC volume in RL, TC, and translabyrinthine (TL) approaches, and quantified the relationship between RL corridor width and IAC exposure. Methods: Thirteen cadaveric temporal bones (7 left, 6 right) underwent high-resolution CT and 3D segmentation pre- and post-mastoidectomy. Endoscopic views at 0° and 30° simulated RL and TC exposures on post-dissection bones ([ Fig. 1 ]); TL was assigned 100% for comparison. Pre-dissection measurements included accessible IAC volume, surgical freedom ([ Fig. 2 ]), angle of attack ([ Fig. 3 ]), and sinodural angle. RL corridor width was defined as the distance between the posterior fossa plate and posterior semicircular canal. Results: The mean IAC volume was 232.8 ± 85.1 mm 3 . Compared with 0° views, 30° endoscopy improved median IAC exposure (RL: 75.6% vs 65.1%, p=.019; TC: 95.6% vs 79.3%, p TC: 245.0 mm 2 > RL: 182.9 mm 2 , p 29.9° > 19.9°, p6 mm (n=5) vs