Rethinking the Collateral Vasculature Assessment in Acute Ischemic Stroke: The Comprehensive Collateral Cascade

Occlusion of a cervical or cerebral artery results in disruption of blood flow to the brain and may result in irreversible infarction. Intracranial pial collaterals are a network of arteries that may preserve blood flow to otherwise critically hypoperfused brain areas until vessel recanalization is achieved. The robustness of these arterial collaterals is pivotal for the survivability of ischemic brain tissue and is associated with treatment success and long-term clinical outcome. More recently, the importance of venous outflow from ischemic brain tissue has been appreciated. Arterial collaterals and venous outflow are evaluated by neuroimaging parameters, and recent imaging advances have enabled a more comprehensive assessment of the entire collateral cascade in patients with acute ischemic stroke. Here we review novel imaging biomarkers for the assessment of arterial collaterals, tissue-level collateral blood flow, and venous outflow. We also summarize how a more comprehensive assessment of the cerebral blood flow leads to a better prediction of treatment efficacy and improved clinical outcomes.