Collateral Circulation in Acute Ischemic Stroke With Large Vessel Occlusion

Inclusion Criteria: * Patients with acute ischemic stroke. * Large vessel occlusion of an intracranial internal artery: M1, M2 or TICA. (terminal intracranial carotid artery), as demonstrated by CTA. * CTA performed within the first 24 hours after stroke onset. Patients with wake-up stroke are included. * A previous modified Rankin Scale score of 0 to 3. * The patient or a legal representative signs a written consent to participate. Exclusion Criteria: * More than 24 hours from last been known to be well. * Occlusion of other arterial segments (vertebrobasilar circulation, A1, P1, M3, M4). * Age below 18 years.