A, The anterior cerebral arteries course above the optic chiasm and in front of the lamina terminalis. The carotid arteries exit the cavernous sinus and pass upward in the lateral margins of the suprasellar area. The superior hypophyseal arteries cross the chiasmatic cistern to reach the lower margin of the chiasm and pituitary stalk. B, Superior view of the suprasellar region. The floor of the third ventricle has been exposed from the suprachiasmatic recess anteriorly to the level of the aqueduct posterior. The anterior cerebral arteries pass above the chiasm. The posterior communicating arteries pass backward below the floor of the third ventricle. The basilar artery bifurcates into the posterior cerebral arteries below the floor of the third ventricle. C, Superior view of the suprasellar region. The carotid arteries course along the lateral margin of the chiasmatic cistern. The basilar bifurcation is located above and behind the sella. The posterior communicating arteries travel backward across the dorsum to join the posterior cerebral arteries. The posterior communicating arteries usually course above and medial to the oculomotor nerves. D, The optic chiasm is positioned above the diaphragm and sella. The optic tracts extends backward and laterally above the posterior cerebral arteries and oculomotor nerves toward the lateral geniculate bodies. The basilar bifurcation has been retracted forward to show the perforating arteries entering the midbrain, which can be damaged in the transsphenoidal approach if the posterior wall of the capsule of a pituitary adenoma is opened. E, Diagrammatic view of the arteries in the suprasellar area, which can be stretched over the margin of a large tumor with suprasellar extension. All of the components of the circle of Willis and their perforating branches can be stretched over the dome of these tumors. F, Superolateral view of the left optic nerve, chiasm, and tract and the floor of the third ventricle. The optic tract extends backward from the optic chiasm, around the upper edge of the cerebral peduncle, and above the posterior cerebral artery. The anterior cerebral arteries pass in front of the lamina terminalis and around the corpus callosum. G, Some of the anterior part of the left cerebral peduncle has been removed while preserving the optic tract. The posterior cerebral and terminal part of the posterior communicating artery can be seen through the interval between the floor of the third ventricle and the optic tract. (Images courtesy of AL Rhoton, Jr.)