Quantitative Analysis of Surgical Exposure and Angle of Surgical Freedom Obtained by Endoscope and Microscope in the Retrosigmoid and Various Posterior Petrosectomy Approaches to the Petroclival Region Using CT-Based Frameless Stereotaxy

Objective: Several approaches are used to expose the petroclival region and most of them require a certain degree of temporal bone resection with its associated approach morbidity, such as hearing and facial nerve compromise. To gain insight into the benefits of integration of endoscopy, we evaluated and compared the exposure obtained by endoscope and microscope in the retrosigmoid and the presigmoid approaches by quantitative analysis.

Methods: We performed a total of 16 operations including retrosigmoid (RS), retrolabyrinthine (RL), translabyrinthine (TL), and transcochlear approaches (TC), bilaterally in two whole, fresh cadaveric heads. We used a navigation system and estimated the working area of the petroclival region and surgical freedom with each approach, using a rigid endoscope 4.0 mm in diameter and 18 cm long with 0-degree and 30-degree lenses, as well as a microscope.

Results:The TC approach provided the largest mean working area (502 mm²) at the brainstem area compared to all other approaches. With the introduction of the endoscope, the working area for 30-degree angled endoscopic RS approach (460 ± 49.7 mm²) was significantly greater than that for the microscopic approach (235 ± 25 mm²; P = 0.002). On the other hand, surgical freedom was significantly decreased with the use of the endoscope compared to microscope use at all stages (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 petroclival region. However, operability as assessed by our surgical freedom model was better with the microscope than with the endoscope.