A cerebrovascular accident, or "stroke", is major injury to brain tissue resulting from a disorder in brain circulation. The human brain demands a disproportional amount of the body's cardiac output and oxygen delivery, and is extremely sensitive to hypoperfusion and ischemia. With total cessation of blood flow as in cardiac arrest, brain death ensues in about four minutes. Local flow limitation results in localized damage.
A transient ischemic attack (TIA) is defined as an event that lasts less than 24 hours and leaves no permanent neurologic defecit. A prototypical example of a TIA is brief unilateral loss of vision (amaurosis fugax) due to platelet emboli from carotid plaque embolizing to the ophthalmic artery at the carotid siphon. TIAs are a portent of the potential for a stroke in a quarter of individuals within the next year and a half.
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