Transpterygoid versus Endoscopic Infracochlear Approaches to the Petrous Apex: A Comparative Cadaveric Study

Background: Surgical access to lesions of the petrous apex is challenging; however, it can be obtained using several approaches such as the endonasal transpterygoid and infracochlear approaches. Various studies have reported on anatomic distances among key anatomic structures within the petrous apex when using these approaches; nonetheless, the afforded surgical maneuverability remains undefined. The purpose of this study was to compare the surgical freedom, area of exposure, and angle of attack of afforded by the endonasal transpterygoid with those of the infracochlear approach.

Methods: Five embalmed, latex injected, cadaveric specimens were dissected bilaterally; taking measurements using the Cartesian coordinates X, Y, and Z with a surgical navigation system .Bilateral endonasal transpterygoid and infracochlear approaches were performed and measurements of surgical freedom, area of exposure, and angle of attack were calculated

Results: Surgical freedom, exposure, and vertical and horizontal angle of attack were assessed. Median surgical freedom for the infracochlear approach was 87.55 (range: 12.21–99.76 degrees) while the median for the transpterygoid approach was 62.71 (range: 13.01–83.88) (Table 1). Median surgical exposure for the infracochlear approach was 44.79 (range: 12.21–74.73), while the median for the transpterygoid approach was 44.76 (range: 20.93–107.16) (Table 2). As for angle of attack of the infracochlear approach, its median V-angle was 0.29 (range: 0.05–0.81), while for the transpterygoid approach was 0.29 (range: 0.12–0.60) (Table 3). The median H-angle for the infracochlear approach was 0.49 (range: 0.24–1.31), while the median for the transpterygoid approach was 0.33 (range: 0.10–1.00) (Table 3).

Conclusion: The results from these studies identify a wide range in all measurements obtained and no statistically significant differences with several potential explanations and implications of these results in decision making. There are a variety of factors to consider in choosing the best approach including anatomic limitations and location of the lesion within the petrous apex. Also, while there was a wide variability among specimens, oftentimes one approach scored much better than the others. This implies that one may be able to identify preoperatively which approach may provide the best surgical freedom and attack for resection of the lesion in each patient. A significant limitation of the study is that cadaveric specimens present normal petrous apex anatomy. In a clinical scenario, a lesion may distort or expand the anatomic limitations of each approach. This must be factored in to guide the choice for a particular surgical approach to the petrous apex.

No conflict of interest has been declared by the author(s).