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Introduction: A previous SAMMPRIS analysis showed that stroke as the qualifying event and old infarct in the territory of the stenosis were independently associated with recurrent stroke in the medical arm. We sought to refine these findings by characterizing the relationships between the patterns of infarcts on baseline brain imaging, collateral flow, and risk of stroke.Methods: In the medical arm of SAMMPRIS, 101 patients had acute infarcts in the territory of a stenotic MCA or ICA stenosis on baseline imaging. Blinded to patient outcome, infarcts were characterized as involving primarily the core MCA, internal or cortical borderzone (BZN), or perforator territories. Among these 3 subgroups, the time to primary endpoint (logrank test) and collateral blood flow on baseline angiography (Chi-square tests) were compared. Old infarcts in the same territory were also characterized according to infarct patterns and correlated with acute infarct patterns and outcome.Results: The table shows rates of stroke in the territory during follow-up in the 3 groups of patients (n = 101) with different acute infarct patterns. Data on collaterals were available in 82/101 patients. Among those, no or partial collaterals were seen in 30/43 patients (70%) with acute BDZ, 7/19 (37%) with core MCA, and 11/20 (55%) with perforator patterns (p = 0.049). Old infarcts in the territory on baseline imaging were also seen in 30/101 patients. Among those, recurrent stroke in the territory occurred in 12/30 (40%), all of whom had either an acute or old BDZ infarct on baseline imaging. Of 14 patients with both acute and old BDZ infarcts on baseline imaging, 50% had a recurrent stroke in the territory during follow-up.Conclusion: Infarct patterns in patients with intracranial stenosis presenting with stroke help refine risk stratification. BDZ infarcts are usually associated with impaired collateral flow and are predictive of a particularly high risk of recurrent stroke during follow-up.