This young woman presented with a spontaneous carotid dissection and extensive watershed infarction between underperfused MCA territory on the left and ACA / PCA. The perfusion maps correctly identified an ischemic penumbra encompassing most of the cortex, which was being supplied by collaterals, encouraged by maximal vasodilatation. 

Carotid stent placement re-established cortical perfusion and saved this patient from a devastating stroke.