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These investigators studied the impact of clot location in patients with acute stroke receiving IV thrombolysis. Four locations (ICA, proximal M1, distal M1, and M2 segment and more distal) of clots were correlated with CT perfusion maps, mismatches, salvaged brain volumes, and outcomes in 105 patients. Clots that were more proximal in location produced larger perfusion defects and lesion volumes. The amount of tissue salvaged was greater in patients with more distally located clots. In conclusion, admission CBV defects were larger in proximal vessel occlusions. More of the penumbra was salvaged if the occlusion was located more distally. This effect reached a plateau in the distal M1 segment of the MCA.

This article addresses the importance of collateral circulation in preserving the tissues contained within the ischemic penumbra in patients with acute stroke treated with IV thrombolysis. The authors evaluated not only the presence of collaterals but also their quality. They quantified a normalized collateral circulation deficit and correlated it with parameters thought to affect its quality, such as baseline NIHSS score, volume of DWI abnormalities, and modified Rankin scale at 3 months. The normalized collateral circulation deficit correlated with NIHSS, lesion volume as seen on DWI, and recanalization at 24 hours. Full recanalization as well as the probability of full recanalization also correlated with the normalized collateral circulation deficit. Thus, this index is a good predictor of recanalization and outcome in patients with acute stroke treated with IV thrombolysis.