A hyperdense basilar artery is noted, consistent with acute thrombotic or embolic disease at the basilar tip with occlusion at the basilar tip on the CT angiographic images (not shown) There is hypoattenuation and loss of grey-white matter differentiation at the left posterior cerebral artery territory consistent with established infarction. This is reflected in the perfusion images with marked prolongation of Tmax and reduced CBF/CBV (not shown). There is also some hypoattenuation at the thalamus on the left and probably involving the left side of the midbrain.