Endoscopic endonasal transclival approach and retrosigmoid approach to the clival and petroclival regions.

OBJECTIVE: The removal of clival lesions, mainly those located intradurally and with a limited lateral extension, may be challenging because of the lack of a surgical corridor that would allow exposure of the entire lesion surface. In this anatomic study, we explored the clival/petroclival area and the cerebellopontine angle via both the endonasal and retrosigmoid endoscopic routes, aiming to describe the respective degree of exposure and visual limitations.
METHODS: Twelve fresh cadaver heads were positioned to simulate a semisitting position, thus enabling the use of both endonasal and retrosigmoid routes, which were explored using a 4-mm rigid endoscope as the sole visualizing tool.
RESULTS: The comparison of the 2 endoscopic surgical views (endonasal and retrosigmoid) allowed us to define 3 subregions over the clival area (cranial, middle, and caudal levels) when explored via the endonasal route. The definition of these subregions was based on the identification of some anatomic landmarks (the internal carotid artery from the lacerum to the intradural segment, the abducens nerve, and the hypoglossal canal) that limit the bone opening via the endonasal route and the natural well-established corridors via the retrosigmoid route.
CONCLUSION: Different endoscopic surgical corridors can be delineated with the endonasal transclival and retrosigmoid approaches to the clival/petroclival area. Some relevant neurovascular structures may limit the extension of the approach and the view via both routes. The combination of the 2 approaches may improve the visualization in this challenging area.