2026 Poster Presentations
P094: RADIOMORPHOMETRIC COMPARISON OF ENDOSCOPIC PRESIGMOID HEARING-PRESERVING APPROACHES TO THE INTERNAL AUDITORY CANAL
Aaron Tucker, BA; Sammy Gao, BA; Brendon Warner, MD; Arman Saeedi, MD, MPH; Lawrance Lee, MD; Nauman F Manzoor, MD; Virginia Commonwealth University Department of Otolaryngology - Head and Neck Surgery
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 (Figure 1); TL was assigned 100% for comparison. Pre-dissection measurements included accessible IAC volume, surgical freedom (Figure 2), angle of attack (Figure 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 mm³. 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<.0001). TC provided greater exposure than RL but less than TL (100%) in both 0° and 30° views. Stepwise increases were seen for median surgical freedom (TL: 330.3 mm² > TC: 245.0 mm² > RL: 182.9 mm², p<.0001) and angle of attack (56.6° > 29.9° > 19.9°, p<.0001). RL corridor width ranged 2.23–8.03 mm (median 4.37 mm) and sinodural angle ranged 57.7° to 96.5° (median = 76.4°). Corridor width >6 mm (n=5) vs <6 mm (n=8) did not reveal changes in exposure. Corridor width correlated with TC 0° exposure (r=0.655, p=.015) but not TC 30° or RL exposures. Surgical freedom correlated with RL exposure for 0° (rho=.627, p=.022) and 30° views (rho=.591, p=.033); angle of attack and sinodural angle were not associated with presigmoid exposure volumes.
Conclusions: Presigmoid hearing-preserving approaches provide less IAC exposure than TL, but angled endoscopes substantially improve lateral IAC visualization. While TC increases exposure more than RL, it is more traumatic to the labyrinth; RL remains a safer hearing-preserving option. In this limited cadaveric series, retrolabyrinthine corridor width was not predictive of RL exposure but instead correlated with TC 0° exposure. Larger feasibility studies should further assess its prognostic value in surgical planning.
