Pathophysiology
Clinical meaning
Stroke is classified into ischemic (87%) and hemorrhagic (13% โ intracerebral hemorrhage 10%, subarachnoid hemorrhage 3%). Ischemic stroke subtypes follow the TOAST classification: (1) Large artery atherosclerosis (carotid or intracranial stenosis โฅ50% โ 20%), (2) Cardioembolism (atrial fibrillation, valvular disease, ventricular thrombus โ 25%), (3) Small vessel occlusion/lacunar (lipohyalinosis of penetrating arterioles โ 25%), (4) Stroke of other determined etiology (dissection, hypercoagulable state, vasculitis โ 5%), (5) Stroke of undetermined etiology (cryptogenic โ 25%). Diagnostic approach: The initial priority is distinguishing ischemic from hemorrhagic stroke because treatment is diametrically opposite (thrombolysis for ischemic; reverse anticoagulation and consider surgery for hemorrhagic). Non-contrast CT head is the first-line emergent study โ it identifies hemorrhage within minutes (appears hyperdense/white) and excludes stroke mimics (tumor, abscess). Early ischemic changes on CT (loss of gray-white differentiation, sulcal effacement, hyperdense vessel sign) may be present but CT is often normal in early ischemic stroke. CT angiography (CTA) identifies large vessel occlusion (LVO) for thrombectomy consideration. CT perfusion (CTP) identifies ischemic core vs. salvageable penumbra. MRI with diffusion-weighted imaging (DWI) is the most sensitive test for acute...