Expanding Access to the Petrous Apex and Petroclival Region Using the Contralateral Transmaxillary Approach with the Addition of Transpterygoid Drilling

Background: When approaching the petrous apex and petroclivcal region, endoscopic transnasal surgery serves as an alternative to transcranial approaches for the midline skull base lesions. However, lateral access is limited due to the steep angle through the nasal access, especially in the area behind the petrous internal carotid artery (ICA) and, ultimately, in the cerebellopontine angle. Recently, the contralateral transaxillary (CTM) approach has been reported as a more direct trajectory providing a more parallel angle to the petrous ICA. Nevertheless, lateral access to petrous bone drilling using this approach can become limited by the pterygoid process and the lateral buttress of the maxillary sinus. Therefore, we aimed to explore the contralateral transmaxillary transpterygoid (CTMP) approach with and without removal of the lateral buttress of the maxillary sinus to further expand access to the petroclival area.

Methods: Ten sides of five formalin-fixed, latex-injected anatomical specimens were dissected to compare the CTM, CTMP, and CTMP with lateral buttress removal (CTMP-LBR). In addition, 30 sides of nonpathological computed topography angiography (CTA) scans were used to obtain digital measurements for the three approaches. The petrous bone was progressive drilled posteriorly and laterally with the goal of reaching the medial cochlea without violating the petrous ICA. During the anatomical dissection of the CTMP-LBR, the periosteum encasing the infratemporal fossa musculature was left intact and the musculature was retracted posteriorly. The instrumentation to the petrous apex is not performed through the musculature.

Results: Compared with the CTM approach, the CTMP and CTMP-LB offered increased access for drilling of the retrocarotid petrous bone (p < 0.001) and a wider angle relative to midline (p < 0.001) in both our radiographic and cadaveric measurements. Approximately 70% of retrocarotid petrous bone could be accessed with CTM, which increased to 83% with CTMP and 100% with CTMP-LBR in radiographic measurements. Radiographically, the CTMP approach necessitated a median of 4 mm of pterygoid drilling, while the CTMP-LBR required a median of 9 mm of pterygoid drilling. Importantly, in the CTMP-LBR, only a median of 11 mm of soft tissue displacement in the infratemporal fossa was required to obtain an angle parallel to the of the petrous ICA. Overall, 50% of cadaveric dissections required CTMP to reach the IAC, 30% required CTMP-LBR, and 20% required CTM alone. In the radiographic measurements, patients with larger angles of the petrous ICA compared with the horizontal plane were more likely to benefit from CTMP than CTM to obtain maximal lateral access in the petrous bone (p = 0.005).

Conclusion: CTMP, the modification of the CTM with the additional pterygoid drilling, with or without removal of the lateral buttress can increase access to the petroclival area, especially the inferior petrous apex. Following removal of the lateral buttress, minimal soft tissue compression within the infratemporal fossa is required to achieve a surgical angle parallel to that of the petrous ICA. Preoperative assessment of the petrous ICA angle may be useful in selecting whether CTM versus CTMP should be employed to maximize access to the petroclival area and intraoperative safe maneuvers surrounding this area.

Publication History

Article published online:
07 February 2025