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Background: There are limited data on the specific mechanisms of stroke in patients with intracranial atherosclerotic stenosis (ICAS). We undertook this study to describe infarct patterns and likely mechanisms of stroke in a large cohort of patients with ICAS, and to evaluate the relationship of these infarct patterns to angiographic features (collaterals, stenosis location and stenosis severity)., Methods: We evaluated infarct patterns in the territory of a stenotic intracranial artery on neuroimaging performed at baseline and during follow-up if a recurrent stroke occurred in patients enrolled in the Warfarin-Aspirin Symptomatic Intracranial Disease (WASID) trial. We defined the likely mechanism of stroke (artery-to-artery embolism, perforator occlusion, hypoperfusion or mixed) according to the site of ICAS and based on the infarct patterns on neuroimaging. Collaterals were assessed using American Society of Interventional and Therapeutic Neuroradiology/Society of Interventional Radiology (ASITN/SIR) grades, and stenosis severity using the WASID trial's measurement technique. We evaluated the association of infarct patterns with angiographic features using χ(2) tests., Results: The likely mechanisms of stroke based on the infarct patterns at baseline in the 136 patients included in the study were artery-to-artery embolism (n = 69; 50.7%), perforator occlusion (n = 34; 25%), hypoperfusion (n = 12; 8.8%) and mixed (n = 21; 15.5%). Perforator-occlusive infarcts were more frequent in the posterior circulation, and mixed patterns were more prevalent in the anterior circulation (both p < 0.01). Most of the mixed patterns in the anterior circulation combined small pial or scattered multiple cortical infarcts with infarcts in border-zone regions, especially the cortical ones. Isolated border-zone infarcts were not significantly associated with a poor grading for collaterals or the severity of stenosis. Among 47 patients with a recurrent infarct during follow-up, the infarct patterns suggested an artery-to-artery embolic mechanism in 29 (61.7%)., Conclusions: Artery-to-artery embolism is probably the most common mechanism of stroke in both the anterior and the posterior circulations in patients with ICAS. An extension of intracranial atherosclerosis at the site of stenosis into adjacent perforators also appears to be a common mechanism of stroke, particularly in the posterior circulation, whereas hypoperfusion as the sole mechanism is relatively uncommon. Further research is important to accurately establish the specific mechanisms of stroke in patients with ICAS, since preliminary data suggest that the underlying mechanism of stroke is an important determinant of prognosis., (© 2014 S. Karger AG, Basel.)

Objective: Stroke risk due to intracranial atherosclerosis increases with degree of arterial stenosis. We evaluated the previously unexplored role of collaterals in modifying stroke risk in intracranial atherosclerosis and impact on subsequent stroke characteristics., Methods: Collateral flow was graded in blind fashion on 287 of 569 baseline angiograms (stenoses of 50-99% and adequate collateral views) in the Warfarin--Aspirin Symptomatic Intracranial Disease (WASID) trial. Statistical models predicted stroke in the symptomatic arterial territory based on collateral flow grade, percentage of stenosis, and previously demonstrated independent covariates., Results: Across all stenoses, extent of collaterals was a predictor for subsequent stroke in the symptomatic arterial territory (hazard ratio [HR] none vs good, 1.14; 95% confidence interval [CI], 0.39-3.30; poor vs good, 4.36; 95% CI, 1.46-13.07; p < 0.0001). For 70 to 99% stenoses, more extensive collaterals diminished risk of subsequent territorial stroke (HR none vs good, 4.60; 95% CI, 1.03-20.56; poor vs good, 5.90; 95% CI, 1.25-27.81; p = 0.0427). At milder degrees of stenoses (50-69%), presence of collaterals was associated with greater likelihood of subsequent stroke (HR none vs good, 0.18; 95% CI, 0.04-0.82; poor vs good, 1.78; 95% CI, 0.37-8.57; p < 0.0001). In multivariate analyses, extent of collaterals was an independent predictor for subsequent stroke in the symptomatic arterial territory (HR none vs good, 1.62; 95% CI, 0.52-5.11; poor vs good, 4.78; 95% CI, 1.55-14.7; p = 0.0019)., Interpretation: Collateral circulation is a potent determinant of stroke risk in intracranial atherosclerosis, demonstrating a protective role with severe stenoses and identifying more unstable milder stenoses., (Copyright © 2011 American Neurological Association.)

Collateral circulation in intracranial atherosclerosis has never been systematically characterized. We investigated collaterals in a multicenter trial of symptomatic intracranial atherosclerotic disease. Baseline angiography was reviewed for information on collaterals in stenoses of the internal carotid, middle cerebral, vertebral, and basilar arteries. A battery of angiographic scales was utilized to evaluate lesion site, arterial patency, antegrade flow, downstream territorial perfusion, and collateral circulation, blinded to all other data. Collateral circulation was adequately available for analysis in 287/569 (50%) subjects with proximal arterial stenoses ranging from 50% to 99%. Extent of collaterals was absent or none in 69%, slow or minimal in 10%, more rapid, yet incomplete perfusion of territory in 7%, complete but delayed perfusion in 11%, and rapid, complete collateral perfusion in 4%. Extent of collateral flow correlated with percentage of stenosis (P<0.0001), with more severe stenoses exhibiting greater compensation via collaterals. Overall, collateral grade increased with diminished antegrade flow across the lesion (thrombolysis in myocardial ischemia) and resultant downstream perfusion (thrombolysis in cerebral infarction) (both P<0.001). Our findings provide the initial detailed description of collaterals across a variety of stenoses, suggesting that collateral perfusion is a pivotal component in pathophysiology of intracranial atherosclerosis and implicating the need for further evaluation in ongoing studies.

BackgroundIntracranial atherosclerotic disease (ICAD) is a common cause of ischemic stroke with a high risk of clinical stroke recurrence. Multiple mechanisms may underlie cerebral ischemia in this condition. The study's objective is to discern the mechanisms of recurrent ischemia in ICAD through imaging biomarkers of impaired antegrade flow, poor distal perfusion, abnormal vasoreactivity, and artery-to-artery embolism.MethodsThis prospective multicenter observational study enrolled patients with recent (≤21 days) ischemic stroke or transient ischemic attack (TIA) caused by ICAD with 50-99% stenosis treated medically. We obtained baseline quantitative MRA (QMRA), perfusion MRI (PWI), transcranial Doppler vasoreactivity (VMR), and emboli detection studies (EDS). The primary outcome was ischemic stroke in the territory of the stenotic artery within 1 year of follow-up; secondary outcomes were TIA at 1 year and new infarcts in the territory on MRI at 6-8 weeks.ResultsAmongst 102 of 105 participants with clinical follow-up (mean 253±131 days), the primary outcome occurred in 8.8% (12.7/100 patient-years), while 5.9% (8.5/100 patient-years) had a TIA. A new infarct in the territory of the symptomatic artery was noted in 24.7% at 6-8 weeks. A low flow state on QMRA was noted in 25.5%, poor distal perfusion on PWI in 43.5%, impaired vasoreactivity on VMR in 67.5%, and microemboli on EDS in 39.0%. No significant association was identified between these imaging biomarkers and primary or secondary outcomes.ConclusionsDespite intensive medical management in ICAD, there is a high risk of clinical cerebrovascular events at 1 year and an even higher risk of new imaging-evident infarcts in the subacute period after index stroke. Hemodynamic and plaque instability biomarkers did not identify a higher risk group. Further work is needed to identify mechanisms of ischemic stroke and infarct recurrence and their consequence on long-term physical and cognitive outcomes.Trial registrationClinicalTrials.gov: NCT02121028.