Neuroscience/Objectives/Lecture 52

From PhysioWiki

Stroke

Characterize the two main types of stroke.

Ischemic stroke

Accounting for 85% of events, ischemic strokes can be divided into several categories:

• Large vessel atherothrombosis
• Cardiogenic embolism (usually from atrial fibrillation)
• Lacunar small vessel disease (small, deep strokes)
• Other or cryptogenic (eg, dissection; usually in young patients without vascular risk factors)

Transient ischemic attacks have a 35% chance of developing into ischemic stroke.

Hemorrhagic stroke

Caused by intracerebral (67%) and subarachnoid hemorrhage (33%), hemorrhagic strokes account for 15% of all strokes.

List the major stroke risk factors.

Modifiable

• Hypertension (ie, BP > 140/85; treat with antihypertensive agents)
• Atrial fibrillation (afib patients have 5-6 times the risk for stroke; treat with anticoagulants)
• Carotid stenosis (addressed with endarterectomy)
• Hypercholesterolemia (can be treated with statins that inhbit HMG-CoA reductase)
• Tobacco
• Diabetes mellitus
• Alcoholism
• Physical inactivity
• Aortic arch atheroma
• Cardiac disease (eg, prior myocardial infarction)
• Hypercoagulable states
• Prior TIA or stroke
• Elevated serum homocysteine

Nonmodifiable

• Age
• Gender
• Race/ethnicity
• Heredity

Recognize major stroke syndromes and their anatomical localization.

Middle cerebral artery

The middle cerebral artery supplies the entire lateral surface of the cerebral hemispheres, the orbitofrontal cortex, and the medial temporal lobe. Therefore patients with middle cerebral artery strokes commonly present with contralateral hemiparesis (face and arm weaker than leg), contralateral hemisensory loss, aphasia (if dominant hemisphere is involved), and contralateral hemianopsia. The contralateral hemiparesis affects the face and arm more than the legs because the legs are represented on the internal surface of the somatosensory cortex, which is supplied by the anterior cerebral artery.

Anterior cerebral artery

The anterior cerebral artery supplies most of the facing surfaces of the hemispheres (within the longitudinal fissure), except for the occipital lobe, which is supplied by the posterior cerebral artery. Consequently patients with anterior cerebral artery stroke present with contralateral lower extremity weakness (for reasons discussed above) and transcortical motor aphasia (if dominant hemisphere is involved).

Posterior cerebral artery

The posterior cerebral artery supplies the occipital lobe and inferior portions of the temporal lobe (including parts of the medial temporal lobe). A stroke involving this artery therefore results in contralateral hemianopsia. Anterograde amnesia may result as well if the medial temporal lobe is involved.

Vertebrobasilar

The vertebral and basilar arteries and their branches mostly supply the brainstem and cerebellum. Consequently, strokes involving these arteries present with cranial nerve and cerebellar dysfunction.

Describe therapeutic approaches to stroke.

Preventive

Preventive approaches mainly aim to control vascular risk factors as discussed earlier. Cardioembolic stroke is prevented with anticoagulation, carotid stenosis with carotid endarterectomy, small vessel lacunar strokes with antiplatelet agents (eg, aspirin, aggrenox), and intracranial atherosclerosis with antiplatelet or antigoagulation agents.

Acute management

Within three hours of symptom onset, tPA (tissue plasminogen activator) should be administered. Immediate head CT should be ordered (although diffusion-weighted MRI is the gold standard) and blood pressure should not be lowered in most circumstances. Anticoagulation with heparin has not shown efficacious in acute stroke treatment. If not treated with tPA, acute ischemic stroke patients should be treated with aspirin therapy acutely.