Inferior View of Basal Cisterns. C, Inferior view of the basal cisterns. The supratentorial cisterns defined in this study are the pericallosal (purple); lamina terminalis (bright green); olfactory (aqua); chiasmatic (red); carotid (yellow); interpeduncular (green); sylvian (dark blue); crural (rose); and oculomotor (light blue). The ambient cistern (not shown) is positioned posterior to the crural cistern between the midbrain and the part of the medial temporal lobe behind the uncus. The confluent area at the junction of the carotid, interpeduncular, and crural cisterns is not shaded. The pericallosal cistern is situated in the interhemisphere fissure on the outer surface of the corpus callosum and contains the anterior cerebral arteries. The lamina terminalis cistern is positioned above the optic chiasm and anterior to the lamina terminalis between the frontal lobes and contains the distal A1 and proximal A2 and the anterior communicating arteries. The chiasmatic cistern surrounds the optic nerves and chiasm and contains the pituitary stalk and carotid perforating branches. The interpeduncular cistern is situated between the cerebral peduncles and the leaves of Liliequist’s membrane at the confluence of the supra- and infratentorial parts of the subarachnoid space and contains the basilar bifurcation and P1. The carotid cistern is situated between the lateral edge of the optic chiasm medially, the temporal lobes laterally, and the anterior perforated substance above and contains the carotid and posterior communicating arteries and the origin of the anterior and middle cerebral, ophthalmic, and anterior choroidal arteries. The sylvian cistern is situated between the frontal and parietal lobes above and the temporal lobes below and contains the M1, M2, and M3 segments of the middle cerebral artery. The oculomotor cistern is formed by the confluence of the inner and the outer arachnoid membranes, which converge to surround the oculomotor nerve. The crural cistern is located between the cerebral peduncle and posterior part of the uncus. The crural and ambient cisterns contain the P2 segment of the posterior cerebral artery and some of the P1 and P2 branches. (Images courtesy of AL Rhoton, Jr.)