IMAGING IN STROKE

OVERVIEW• Introduction• Pathophysiology• Anatomy (arterial distribution)• Stroke protocol• CT features• MRI features• Perfusion studies• Angiography• Difference between arterial and venous infarcts• Conclusion

INTRODUCTION• Stroke, or cerebrovascular accident (CVA), is a clinical term that describes a sudden loss of neurologic function persisting for more than 24 hours that is caused by an interruption of the blood supply to the brain.• It is the second leading cause of death worldwide, with considerable disability among survivors.

•Neuroimaging plays a vital role in the workup of acute stroke by providing information essential to accurately triage patients, expedite clinical decision making with regards to treatment, and improve outcomes in patients presenting with acute stroke.

• The goal of imaging in a patient with acute stroke is:• Exclude hemorrhage•Differentiate between irreversibly affected brain tissue and reversibly impaired tissue (dead tissue versus tissue at risk)• Identify stenosis or occlusion of major extra- and intracranial arteries.

TYPES OF STROKE• Ischemic infarct 80%• Intracranial hemorrhage 15%•Non traumatic subarachnoid hemorrhage 5%

PATHOPHYSIOLOGYISCHEMIC STROKE

Vascular occlusion (ischemia)

Cell hypoxia & depletion of

ATP

Loss of ion gradient with

influx of Na and Ca ions in cell

Cytotoxic edema

Glutamate and free radicals

Ischemia

Break down of blood brain

barrier*

• Surrounding the infarct core is tissue with less severe reduction in blood flow that may be salvaged with early reperfusion, termed ischemic penumbra, and oligemic tissue at the periphery. 

• Ischemic strokes may be divided into 3 major subtypes, based on the TOAST classification system:• Large vessel occlusive disease• Lacunar infarction (small vessels disease)• Cardio embolic infarction

HEMORRHAGIC STROKE • The most common etiology of primary hemorrhagic stroke (intracerebral hemorrhage) is hypertension (at least two-thirds of patients).• The remaining cases of spontaneous intra parenchymal hemorrhage may be secondary to vascular malformations or amyloid angiopathy.

SUBARACHNOID HEMORRHAGE

• The most common cause of atraumatic hemorrhage into the subarachnoid space is rupture of an intracranial aneurysm.• Berry aneurysm or saccular aneurysms.*

ANATOMY (ARTERIAL DISTRIBUTION)

• The intracranial circulation can be conveniently divided into anterior and posterior circulation, on the basis of internal carotid artery and vertebral artery supply respectively. 

IMAGING MODALITIES•Unenhanced CT•MRI •DW/PWI• Angiography• Perfusion imaging

IMAGING SHOULD TARGET ASSESSMENT OF 4Ps

• Parenchyma• Pipes: intra and extra cranial circulation • Perfusion• Penumbra

CT FEATURES• CT has the advantage of being available 24 hours a day and is the gold standard for hemorrhage. •On CT 60% of infarcts are seen within 3-6 hours and virtually all are seen in 24 hours. • The overall sensitivity of CT to diagnose stroke is 64% and the specificity is 85%.

•Hypo attenuating brain tissue•Obscuration of lentiform nucleus•Dense MCA sign• Insular ribbon sign• Loss of sulcal effacement

HYPOATTENUATING BRAIN TISSUE

•Hypo attenuation with subtle loss of gray white matter differentiation on CT is highly specific for irreversible ischemic brain damage if it is detected within first 6 hours. 

OBSCURATION OF LENTIFORM NUCLEUS

• Also called blurred basal ganglia, is an important sign of infarction.• Seen in middle cerebral artery infarction and is one of the earliest and most frequently seen signs.*

INSULAR RIBBON SIGN•Hypo density and swelling of the insular cortex.  It is a very indicative and subtle early CT-sign of infarction in the territory of the middle cerebral artery. 

DENSE MCA SIGN

FEATURES ACCORDING TO AGE OF INFARCT

• Immediate • Early hyper acute --- 1-6 hours• Acute --- 24 hours-1 week• Sub acute --- 1-3 weeks• Chronic --- more than 3 weeks