Stroke is a sudden neurologic deficit caused by cerebrovascular ischemia (87%) or hemorrhage (13%). Hemorrhagic strokes may be intracerebral (10% of all strokes) or subarachnoid (3% of all strokes). Stroke is the fourth leading cause of death in the United States and a leading cause of long-term disability.

The American Heart Association (AHA) and the American Stroke Association (ASA) have established tissue-based definitions for ischemic stroke and transient ischemic attack (TIA) that have important implications for assessing and preventing strokes. These definitions encourage early neurodiagnostic imaging following a TIA and risk stratification for subsequent stroke.

■ Ischemic stroke is "an infarction of CNS tissue" that may be symptomatic or silent. "Symptomatic ischemic strokes are manifest by clinical signs of focal or global cerebral, spinal, or retinal dysfunction caused by CNS infarction. A silent stroke is a documented CNS infarction that was asymptomatic."

■ TIA is now defined as "a transient episode of neurological dysfunction caused by focal brain, spinal cord, or retinal ischemia, without acute infarction." The AHA/ASA guidelines recommend neurodiagnostic imaging within 24 hours of symptom onset and routine noninvasive imaging of the carotid and intracranial vessels.

TIAs are a major risk factor for stroke, which occurs in 3% to 10% of patients within 2 days and in 9% to 17% within 90 days. Short-term stroke risk is highest in those with age 60 years and older, diabetes, focal symptoms of weakness or impaired speech, and a TIA lasting more than 10 minutes. One population-based study found a combined risk for recurrent TIA/stroke/and death of 25% within the 3 months following a TIA.

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