Comparison of microscopic and endoscopic view of the internal acoustic meatus: A cadaveric study.

The endoscope is thought to provide an improved exposure of the internal acoustic meatus after retrosigmoid craniotomy for microsurgical resection of intrameatal tumors. The aim of this study is to quantify the differences in internal acoustic meatus (IAM) exposure comparing microscopic and endoscopic visualization. A retrosigmoid approach was performed on 5 cadaver heads. A millimeter gauge was introduced into the internal acoustic meatus, and examinations with a surgical microscope and 0°, 30° and 70° rigid endoscopes were performed. The extent of IAM depth visualized with the microscope and the different angled endoscopes were analyzed. The microscopic view allowed an average IAM depth visualization of 2.8 mm. The endoscope allowed an improved exposure of IAM in all cases. The 0°, 30° and 70° endoscopes permitted an exposure that was respectively 96% (5.5 mm), 139% (6.7 mm) and 200% (8.4 mm) more lateral than the microscopic view. Angled optics, however, provided an image distortion, specifically the 70° endoscope. The endoscope provides a superior visualization of the IAM compared to the microscope when using a retrosigmoid approach. The 30° endoscope represented an ideal compromise of superior visualization with marginal image distortion. Additional implementation of the endoscope into microsurgery of intrameatal tumors likely facilitates complete tumor removal and might spare facial and vestibulocochlear function. Clin. Anat. 31:398-403, 2018. © 2017 Wiley Periodicals, Inc.