Endoscopic Endonasal Transmaxillary Transpterygoid Approach with Eustachian Tube Mobilization and Resection: A Quantitative Anatomical Study

Introduction: The endoscopic endonasal transmaxillary transpterygoid approach can be used to access the petrous apex and the medial petroclival area. Mobilization or resection of the cartilaginous eustachian tube (ET) may provide a wider surgical corridor to access this region in the lateral skull base. In our cadaveric anatomical study, a quantitative evaluation of the impact of these surgical maneuvers on this endoscopic approach has been performed.

Methods: Five adult cadaveric heads injected with colored silicone were dissected bilaterally using 0- and 30-degree endoscopes (Carl Storz) along with standard endoscopic instruments. Three different techniques were compared, respectively, a superolateral ET mobilization, an inferolateral ET mobilization and ET resection. Several measurements were taken using the navigation device (Stealth Medtronic) by placing the probe’s tip onto the selected anatomical target and recording the coordinates for quantification analysis. Parameters included surgical exposure area, ET mobilization distance (ETMD) and surgical freedom.

Results: The superolateral ET mobilization and ET resection provided a significantly increased surgical exposure when compared with the exposure with the ET in a neutral position. The removal of the ET provided a 93% increase in surgical exposure with an average surgical exposure area of 680 ± 93 mm² (p = 0.04), compared with the inferolateral (p = 0.04) and superolateral (p = 0.04) approaches.

The ET mobilization in the superolateral direction resulted in a significantly increased ETMD when compared with the inferolateral direction with a percent difference of 50% (20 ± 5 mm and 10 ± 4 mm, respectively, p = 0.04).

The superolateral ET mobilization delivered a significantly increased angle of attack into the external opening of the hypoglossal canal, jugular vein and carotid artery when compared with both the inferolateral ET mobilization and neutral ET position. The carotid artery was not reachable without ET mobilization.

Conclusion: The endoscopic endonasal transmaxillary transpterygoid approach with ET resection provided the largest surgical exposure. The superolateral ET mobilization might be an alternative adjunct to provide a larger surgical corridor to the petroclival region.