The Right Ambient Cistern and its contents. The image is oriented with superior to the left and anterior towards the top. The ambient cistern, one of the subarachnoid cisterns, is located lateral to the midbrain and posterior to the thalamus.  It contains several blood vessels (posterior cerebral artery, superior cerebellar artery, and basal vein of Rosenthal) in addition to the trochlear nerve.  (Image courtesy of AL Rhoton, Jr.)