Endoscopic Approach to the Middle Clivus. A, View focusing on the middle clivus and foramen lacerum with a 45-degree endoscope directed laterally. The yellow circle in the inset shows the endoscopic field. The pterygoid processes have been removed. Some of the fibrocartilage filling the lower part of the foramen lacerum has been removed to expose the anterior genu of the petrous carotid. The vidian nerve is hidden in the fibrocartilage at the anterolateral margin of the foramen lacerum. B, The vidian canal has been skeletonized. The vidian canal, which conveys the vidian artery and nerve, opens posteriorly into the upper part of the anterolateral edge to the foramen lacerum. The deep petrosal branch of the carotid sympathetic plexus joins the greater petrosal nerve at the foramen lacerum near the posterior opening of the vidian canal to form the vidian nerve. The upper end of the inferior petroclival vein connects through the foramen lacerum with the venous plexus around the carotid artery or with the cavernous sinus. The trapezoid-shaped middle clivus is bordered laterally by the foramen lacerum and internal carotid artery in the upper part and by the petroclival fissure in the lower part. C, Right lateral part of the middle clival area. The right inferior petrosal sinus and adjacent dura have been removed. A thin dural bridge sits at the junction of the upper and middle clivus, and a thin bony bridge separates the middle and lower clivus. The lower part of the pons, basilar and anterior inferior cerebellar arteries, and cisternal part of the abducens nerves are exposed. D, Closer view with the 45-degree endoscope directed laterally. All the cisternal segment of the facial nerve, except the origin, is hidden by the petrous part of the temporal bone. It is difficult to see the whole cisternal segment even with the angled endoscope directed laterally. E, The petrous apex and bone below the distal carotid canal have been removed to expose more of the cisternal segment of the facial and vestibulocochlear nerves. The posterior root of the trigeminal nerve passes forward below the superior petrosal sinus. F, More of the temporal bone below the carotid canal and trigeminal nerve has been drilled. The anterior wall of the internal acoustic meatus has been opened to expose the cisternal and meatal segments of the facial and vestibulocochlear nerves, as well as the premeatal and postmeatal segment of the anterior inferior cerebellar artery. (Images courtesy of AL Rhoton, Jr.)