A, The craniotomy flap and dural opening exposes the temporal lobe and the floor of the middle cranial fossa. The inset shows the site of the scalp incision. B, The temporal lobe has been elevated to expose the posterior cerebral and superior cerebellar arteries. The posterior cerebral artery passes above and the superior cerebellar artery below the oculomotor nerve. The superior cerebellar artery branches course with the trochlear nerve around the side of the brainstem. C, The posterior cerebral artery has been depressed to expose the basilar artery. The anterior choroidal artery arises from the internal carotid artery and passes between the cerebral peduncle and uncus to enter the temporal horn. D, The tentorium has been divided behind the petrous ridge to expose the upper part of the basilar artery, the superior cerebellar artery, and the trigeminal and trochlear nerves. The medial posterior choroidal artery also passes around the lateral side of the brainstem. E, Enlarged view to show the increased length of basilar artery exposed by dividing the tentorium. F, An anterior petrosectomy has been completed. The petrous apex in the area behind the internal carotid artery and medial to the semicircular canals has been removed. The dural opening has been extended downward to expose the lateral edge of the clivus and the inferior petrosal sinus coursing along the petroclival fissure. The abducens nerve and the anteroinferior cerebellar artery are in the lower margin of the exposure. G, The angle of view has been changed to show the vertebral arteries in the lower margin of the exposure. The facial and vestibular nerves and the labyrinth and semicircular canals, which are to be avoided in the anterior petrosectomy approach, have been exposed to show their relationship to the approach. (Images courtesy of AL Rhoton, Jr.)