Stroke Overview

Ischemic Infarction

There are 3 major clinical ischemic stroke subtypes based on the classification from a multicenter clinical trial [trial of drug ORG 10172 in acute stoke treatment (TOAST)]. These 3 subtypes include large artery/atherosclerotic infarctions, cardioembolic infarctions, and small vessel occlusion (lacunar) infarctions.

Large artery/atherosclerotic strokes represent ~ 40% of strokes and can arise from thrombosis at the site of a plaque or from emboli produced at the plaque that lodge downstream. The most common site of atherosclerotic plaque is at the carotid bifurcation with involvement of the distal common carotid artery and the 1st 2 cm of the internal carotid artery. The most frequently occluded intracranial vessel is the middle cerebral artery (MCA). Other common locations for atherosclerotic plaque include the carotid siphon and proximal anterior artery and MCA. The vertebral and basilar arteries are also commonly involved by atherosclerosis.

Cardioembolic disease accounts for 15-25% of ischemic strokes. Risk factors include myocardial infarction, ventricular aneurysm, atrial fibrillation or flutter, cardiomyopathy, and valvular heart disease.

Lacunar infarcts are small in size (< 15 mm), typically in the basal ganglia and thalamus, and account for 15-30% of all strokes. They are often multiple and are due to embolic, atheromatous, or thrombotic lesions in the single penetrating end arterioles that supply the deep gray nuclei, including the lenticulostriate and thalamoperforating arteries. Other common locations for lacunar infarcts include the internal capsule, pons, and corona radiata.

Intraparenchymal Hemorrhage

Intraparenchymal hemorrhage represents ~ 15% of all strokes and includes multiple etiologies. Hypertensive hemorrhage is the most common etiology, representing ~ 40-60% of all primarily intracranial hemorrhages. Other etiologies include amyloid angiopathy in elderly patients, as well as vascular malformations, vasculitis, drugs, and bleeding diathesis.

Risk factors for hemorrhagic stroke include increasing age, hypertension, smoking, excessive alcohol consumption, prior ischemic stroke, abnormal cholesterol, and anticoagulant medications.

Although the MR physics related to hemorrhage are complex, the stages are generally accepted as hyperacute, acute, early subacute, late subacute, and chronic.