Clots, Collaterals, and the Intracranial Arterial Tree

See related article, p 2061. Acute ischemic stroke is a story of two parts; a thrombus blocks anterograde blood flow within the intracranial arterial tree while tiny vessels called collaterals sustain the brain until the thrombus is cleared. The location, size, and type of thrombus along with the degree and extent of collaterals likely determine the patient’s clinical symptoms, the likelihood of treatment success and the patient’s prognosis. A major focus of acute stroke research has been to image and measure various thrombus and collateral characteristics that help predict patient outcomes.In vitro studies show that larger clots are less likely to lyse with thrombolytic agents, whereas clots with more surface area exposed to flowing blood are more likely to lyse early.1 This information can be used to create a theoretical framework for thrombus lysis within the intracranial arterial tree.2 Thrombi in proximal arteries such as the internal carotid or the M1 segment of the middle cerebral artery are likely to have greater volume than thrombi in smaller more distal arteries. Independent of thrombus volume, longer thrombi within the cylindrical framework of the intracranial arterial tree are likely to have less relative surface area (at the proximal and distal ends) exposed to blood flow. Poor collateral status is likely to result …