Intracranial collaterals Assessment in acute ischemic stroke In clinical practice, infarct growth does not always progress to involve the full extent of the vascular territory, even if the affected intracranial artery fails to recanalize. The presence and recruitment of various collateral channels are believed to be responsible for this phenomenon in acute ischemic stroke (AIS). These collaterals may also play an important role in influencing the safety and efficacy of acute revascularization approaches. Although blood supply from the leptomeningeal collaterals may temporarily maintain the ischemic penumbra, the persistence and effectiveness of this alternative circulatory supply is erratic and unpredictable. Some collaterals may disappear over time (collateral failure); this is one of the mechanisms responsible for clinical deterioration following initial improvement.