Significance of good collateral compensation in symptomatic intracranial atherosclerosis

Background: Collateral circulation stabilizes cerebral blood flow in patients with acute occlusion, but its prognostic role is less studied in intracranial atherosclerosis and appears different in moderate to severe stenosis. We aimed to study the associations between antegrade flow across stenosis, collateral flow via leptomeningeal anastomosis, and the neurological outcome and recurrence risk in patients with symptomatic intracranial stenosis.

Methods: We examined a cohort of consecutive patients admitted for stroke or transient ischemic attack (TIA) with symptomatic intracranial stenosis confirmed by digital subtraction angiography in a single-center retrospective study. Angiograms were graded systematically in a blinded fashion for antegrade and collateral flow, using Thrombolysis in Cerebral Infarction (TICI) and American Society of Intervention and Therapeutic Neuroradiology/Society of Interventional Radiology (ASITN/SIR) grading, respectively, and integrated to a simple composite circulation score. Demographic and clinical variables, modified Rankin Scale (mRS) scores at 3 months, recurrent stroke or TIA in 12 months were collected. Uni- and multivariate analyses were performed to identify independent predictors of good outcome (mRS 0-2) and recurrence in a logistic regression model.

Results: Among 69 patients with pure intracranial atherosclerosis ≥ 50%, compromised antegrade flow (TICI 0-2a) was observed in 26 (36%) patients and was associated with more severe arterial stenosis (mean 86 vs. 74%, p = 0.001). Poor collateral compensation resulting in a poor composite circulation score was observed in 8 (12%) patients. Patients with a good circulation score (n = 61, 88%) had preserved flow, which was associated with more favorable outcome (OR 7.50, 95% CI 1.11-50.7, p = 0.04) and less recurrent TIA or stroke (OR 0.18, 95% CI 0.04-0.96, p = 0.04). Prognosis was not significantly associated with antegrade or collateral grade per se.

Conclusion: Good collateral compensations are more important in patients with symptomatic intracranial stenosis and compromised antegrade flow, and are associated with favorable outcome and less recurrence risk. The feasibility of composite flow assessment should be explored in future studies to identify high-risk intracranial stenosis with compromised hemodynamics.