CT perfusion maps in a 51-year-old patient presenting with right-sided hemiparesis who was diagnosed with Moyamoya disease, demonstrating bilateral supraclinoid internal carotid occlusion. CT perfusion maps in a 51-year-old patient presenting with right-sided hemiparesis who was diagnosed with Moyamoya disease, demonstrating bilateral supraclinoid internal carotid occlusion. A, Baseline. B, After ACZ administration. The baseline pre-ACZ PCT (A) demonstrates the typical pattern of Moyamoya disease with decreased CBF and increased MTT and TTP in the bilateral anterior and middle cerebral distributions (arrows). After ACZ challenge (B), the CBF in the anterior circulation decreases consistent with steal phenomenon (B, CBF, arrows). The CBF map demonstrates a normal expected increase in the PCA territories. There is further prolongation of the MTT and TTP in both ACA and MCA distributions (arrowheads, B), consistent with worsening of cerebral hemodynamics after ACZ, and type III physiology. The patient successfully underwent left-sided ECIC bypass surgery. A.S. Vagal et al. AJNR Am J Neuroradiol 2009;30:876-884 ©2009 by American Society of Neuroradiology