Stepwise Exposure of the Upper Clivus. A, The vidian canal courses along the lateral edge of the sinus floor. The palatovaginal canal, located between the sphenoidal process of the palatine bone and the vaginal process of the sphenoid bone, is positioned medial to the vidian canal. B, Enlarged view. The sphenoid septae and pterygoid processes have been removed. The wings (alae) of the vomer attached along the sphenoid sinus floor. The vomerovaginal canal, located between the ala of the vomer and the vaginal process of the sphenoid bone, is more of a shallow bony groove than a canal. The vomerovaginal canals are located medial to the palatovaginal canals seen in A. C, The medial wall of the cavernous sinuses has been opened, and the cavernous segment of the carotid arteries has been exposed. The posterior sinus wall, which is limited superiorly by the sellae and laterally by the paraclival segment of the carotid arteries, corresponds to the part of the clivus formed by the sphenoid bone. D, The right half of the upper clivus has been drilled. The periosteal layer of the clival dura has also been opened to expose the basilar venous plexus. A bundle of the carotid sympathetic plexus ascends on the cavernous carotid and joins the abducens nerve. E, Anterior, oblique view of the right anteromedial cavernous sinus. The venous confluence surrounding the dural porus of the abducens nerve has been removed. The vidian nerve runs below and the cavernous segment of the abducens nerve runs above the lingual process of the sphenoid bone. The vidian nerve, when followed posteriorly, reaches the lateral surface of the lacerum segment of the petrous carotid artery. Here, the nerve turns slightly upward in the foramen lacerum and is continuous with the greater petrosal and the deep petrosal nerves. The abducens nerve, when followed anteriorly, exits its dural porus and ascends lateral to the internal carotid artery. F, The upper clivus has been opened and the dura, above the level of the dural porus of the abducens nerve (yellow arrow), has been removed. The basilar artery and the upper half of the pons are exposed. (Images courtesy of AL Rhoton, Jr.)