Endoscopic endonasal approach to the middle and upper clivus. The meningeal dural layer has been removed bilaterally to expose the intradural structures. The right AICA arises from the basilar trunk. There is a hypoplastic left AICA. The cisternal segment of the abducens nerve can now be identified bilaterally running superiorly to continue as the interdural segment. In the upper clival region we can identify the basilar bifurcation, SCA, PCA, and oculomotor nerves. (Image courtesy of JC Fernandez-Miranda)