Ischemic Diseases - Ischemic stroke accounts for approximately 85% of acute cerebrovascular events. Symptoms of acute ischemic stroke vary based on the functions of the neural tissues supplied by the occluded vessel, and the presence or absence of collateral circulation. The circle of Willis provides extensive collateral circulation, as it connects the right and left carotid arteries to each other and each to the vertebrobasilar system. Patients with complete occlusion of the carotid artery proximal to the circle of Willis may be asymptomatic if the blood flow patterns can shift and provide sufficient circulation to the ipsilateral cerebral hemisphere from the contralateral carotid and the basilar artery. However, the anatomy of the circle of Willis is highly variable. Patients may have a hypoplastic or missing communicating artery, both anterior cerebral arteries supplied by one carotid, or the posterior cerebral artery supplied by the carotid rather than the basilar. Similarly, one vertebral artery is often dominant, and the other hypoplastic. These variations may make disease in a particular vessel more neurologically devastating than in a patient with full collateral circulation. Occlusion distal to the circle of Willis generally results in stroke in the territory supplied by the particular artery.
Neurologic deficit from occlusive disease may be temporary or permanent. A patient with sudden-onset focal neurologic deficit that resolves within 24 hours has had a transient ischemic attack (TIA). If the deficit resolves between 24 hours and 1 week, then the patient has had a reversible ischemic neurologic deficit (RIND). A patient with permanent deficits has had a cerebrovascular accident (CVA). CVA is a commonly used, but vague term. Some prefer the term completed stroke.
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