Endoscopic Approach to the Lower Clivus. G, The right rectus capitis anterior has been removed. The relationship between the posterior nasopharyngeal mucosa and the pharyngeal tubercle is shown. H, The remainder of the posterior nasopharyngeal wall and pterygoid process has been removed. The inferior petroclival vein courses along the extracranial surface of the petroclival fissure. I, 45-degree endoscope has been inserted above the cartilaginous part of eustachian tube and directed laterally to view the jugular foramen and the adjacent area. The petrosal venous confluence at the lower end of the inferior petrosal sinus connects to the venous plexus of the hypoglossal canal and prevertebral venous plexus. In this specimen, the venous confluence empties below the extracranial orifice of the jugular foramen into the medial aspect of the internal jugular vein through openings in the venous walls between the glossopharyngeal and vagus nerves. The inferior petroclival vein also empties into the petrosal venous confluence. J, Some of the petrosal venous confluence has been removed to expose the jugular foramen. The glossopharyngeal nerve exits the jugular foramen along the anterior wall of the internal jugular vein, whereas the vagus and accessory nerve exit along the medial venous wall. The neuromeningeal branch of the ascending pharyngeal artery gives rise to the hypoglossal and jugular branches just below the jugular foramen. Both branches penetrate the petrosal confluence and enter the hypoglossal canal and the jugular foramen to supply the surrounding dura. K, Anterior view of the clivus. L, The lower clivus has been drilled on the right side to expose the medulla. The upper edge of the lower clivus is located approximately 4 mm above the top of the pharyngeal tubercle. (Images courtesy of AL Rhoton, Jr.)