'O' There are two main classifications of cerebral ischemic events: transient ischemic attack (TIA) and cerebral infarction. A TIA is a temporary reduction in perfusion to a focal region of the brain causing a short-lived disturbance of function. TIAs have a rapid onset (5 minutes) and short duration (2-15 minutes, up to 24 hours). The symptoms vary depending on the area of the brain affected; however, no deficit remains after the attack. The classic definition of TIA is based on symptom duration of less than 24 hours, while symptoms lasting 24 hours or greater have been categorized as cerebral infarction. Improved brain imaging techniques have revealed that clinical symptoms lasting greater than 1 hour but less than 24 hours are often cerebral infarction. For this reason, it has been proposed that the definition of TIA be changed to include clinical symptoms lasting less than 1 hour with no evidence of cerebral infarction. A TIA maybe the only warning of an impending stroke, with the greatest risk occurring in the first week. Cerebral infarction is similar to a TIA; however, symptoms last longer than 24 hours, and in 90% of patients residual deficits remain after the event.
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