Clinical meaning
Stroke is the sudden onset of focal neurological deficit caused by cerebrovascular disruption, classified as ischemic (87% of strokes, from arterial occlusion) or hemorrhagic (13%, from vessel rupture). Ischemic stroke occurs through three primary mechanisms: large artery atherosclerosis (atherosclerotic plaque in the carotid or intracranial arteries ruptures, triggering thrombus formation that occludes the vessel), cardioembolism (thrombus forms in the left atrium or ventricle — most commonly from atrial fibrillation — and embolizes to cerebral arteries), and small vessel occlusion (lipohyalinosis of penetrating arterioles from chronic hypertension causes lacunar infarcts in the basal ganglia, thalamus, pons, and internal capsule). The ischemic penumbra concept is central to acute stroke treatment: the infarct core (tissue receiving less than 10-12 mL/100g/min of cerebral blood flow) undergoes irreversible necrosis within minutes, but the surrounding penumbra (tissue with blood flow between 12-22 mL/100g/min) is functionally impaired but structurally viable and salvageable if perfusion is restored promptly — this is the therapeutic target. Imaging confirmation follows a time-critical algorithm: non-contrast CT head is obtained within 25 minutes of arrival (door-to-CT target) to rule out hemorrhage — acute...