Approach to the Upper Clivus. G, View of the right anteromedial cavernous sinus with a 45-degree endoscope directed laterally. The vidian canal opens posteriorly into the anterolateral edge to the foramen lacerum. The ophthalmic and oculomotor nerves run in the lateral wall of the cavernous sinus, and the abducens nerve passes forward in the sinus. The maxillary nerve passes forward below the cavernous sinus. The ophthalmic artery and optic nerve pass above the optic strut in the optic canal. The dural porus of the abducens nerve and basilar venous plexus have been exposed. The vidian nerve passes below and the abducens nerve above the lingual process of the sphenoid. H, View focusing on the right paraclival internal carotid artery. The lingual process of the sphenoid bone has been removed. The petrolingual ligament bridges the interval between the lingual process and petrous apex just below the cavernous sinus. The vidian nerve courses below the petrolingual ligament. The inferolateral trunk arises from the lateral aspect of the horizontal segment of the cavernous carotid, descends lateral to the abducens nerve, and supplies the dura of the inferolateral wall of the cavernous sinus surrounding the foramina rotundum and ovale. I, The petrolingual ligament has been removed, and the petrous apex and the gasserian ganglion have been exposed by retracting the ganglion laterally and the carotid artery medially. J, View of the left anteromedial cavernous sinus with a 45-degree endoscope directed laterally. The upper clivus has been drilled, and the periosteal layer of the clival dura has been opened to expose the venous confluens. K, The venous confluens around the dural porus of the abducens nerve has been removed. The abducens nerve penetrates the dura and ascends lateral to the carotid artery and below the petrosphenoid (Gruber’s) ligament, which extends from the lower part of the lateral edge of the dorsum sellae to the petrous apex. The dorsal meningeal branch of the meningohypophyseal trunk courses below Gruber’s ligament and near the abducens nerve. L, Opening the upper clival dura below the pituitary gland exposes the upper half of the anterior surface of the pons. The outer arachnoid membrane has been opened and retracted laterally. The anterior pontine membranes, located just medial to the dural pori of the abducens nerves, separate the prepontine cistern from the cerebellopontine cisterns. The upper basilar artery and its perforating branches to the pons are well visualized. The rostral limit of the upper clival approach is usually at the pontomesencephalic junction. A duplicate left superior cerebellar artery encircles the brainstem near the pontomesencephalic junction. (Images courtesy of AL Rhoton, Jr.)