Quantitative analysis of surgical exposure and maneuverability associated with the endoscope and the microscope in the retrosigmoid and various posterior petrosectomy approaches to the petroclival region using computer tomograpy-based frameless stereotaxy. A cadaveric study

Object: Most of the approaches used to expose the petro-clival region require a certain degree of temporal bone resection with its associated approach morbidity such as potential hearing and facial nerve compromise. Endoscopes are becoming more and more popular in neurosurgical practice. To gain insight into the benefits of using endoscopy to operate on the petro-clival region, we evaluated and compared the exposure and maneuverability obtained employing the endoscope and the microscope in retrosigmoid and pre-sigmoid approaches by using quantitative analysis based on frameless stereotaxy. Methods: We evaluated the retrosigmoid (RS), retrolabyrinthine (RL), translabyrinthine (TL), and transcochlear (TC) approaches. Each approach was performed 4 times for a total of 16 approaches. We used a navigation system for intraoperative navigation. Each approach was evaluated vis-a-vis the area of the petro-clival/brainstem region exposed and the afforded maneuverability, both using a rigid endoscope or an operating microscope. Results: The TC approach exposed the largest area at the brainstem compared to all other three approaches both in microscopic and endoscopic modes and there was no significant difference between the 2 modes (P = 0.42). In the RS approach use of the 30° angled endoscope increased significantly the exposure compared to the operating microscope (respectively 460 ± 49.7 mm² vs 235 ± 25 mm²; P = 0.002). On the other hand, maneuverability was significantly decreased with the endoscope compared to the microscope in all the approaches evaluated (P = 0.006). Conclusions: Integration of the endoscope into conventional petrosectomy approaches could significantly reduce the amount of temporal bone drilling for adequate visualization of the petro-clival region. However maneuverability as assessed by our model was better with the microscope than with the endoscope.