Endoscopic endonasal approach to the middle clivus. The clival bone has been drilled to expose the clival dura and the paraclival segment of the ICA. The clival dura has two layers, periosteal and meningeal, and the basilar venous plexus runs in between them. Note the petroclival dural fold that is located just above the petrosal process of the sphenoid bone, and serves as a key landmark to identify the abducens nerve at Dorello’s canal. (Image courtesy of JC Fernandez-Miranda)