Ischemic stroke is most commonly due to which mechanism?

• A. A blockage of blood flow to the brain
• B. Bleeding within the brain
• C. Infection
• D. Low blood pressure

Answer: (A)

Ischemic stroke happens when a blood vessel supplying the brain becomes blocked, so that part of the brain is deprived of oxygen and nutrients. This blockage is most often caused by a clot—either a thrombus forming in a brain vessel or an embolus traveling from another part of the body—commonly related to atherosclerosis or conditions like atrial fibrillation. Without quick restoration of blood flow, the affected tissue dies, while surrounding tissue may be saved if perfusion is restored in time, which is why rapid reperfusion therapies are critical. The other options describe scenarios that are not the typical mechanism for ischemic stroke: bleeding inside the brain defines a hemorrhagic stroke, infection is not a stroke cause, and low blood pressure can cause global hypoperfusion but does not explain the common focal arterial blockage that characterizes ischemic stroke.