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Stroke Overview

Introduction

Stroke is a generic term that describes the clinical event of a

sudden onset of neurologic deficit secondary to

cerebrovascular disease. Stroke has 4 main etiologies,

including cerebral infarction (80%), intraparenchymal

hemorrhage (15%), nontraumatic subarachnoid hemorrhage

(5%), and venous infarction (~ 1%). Clinically, ischemic

infarction is the most common etiology and will be the main

topic of this introduction. The principal cause of cerebral

infarction is atherosclerosis and its sequelae.

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