A transient ischemic attack (TIA) has traditionally been defined as a sudden, focal neurologic deficit of presumed vascular origin lasting less than 24 h. The assumptions that TIAs do not result in permanent brain injury and that TIA symptoms disappear because of prompt spontaneous reperfusion have existed for many years. Symptoms lasting more than 24 h are considered to reflect cerebral infarction and represent a stroke. These long-established definitions are, however, no longer compatible with current concepts of brain ischemia; ischemic symptoms lasting more than a few hours often result in brain infarction, irrespective of the time course of clinical resolution. In 2002 a group of cerebrovascular specialists, therefore, proposed that TIA be redefined as "...a brief episode of neurologic dysfunction caused by focal brain or retinal ischemia, with clinical symptoms typically lasting less than one hour, and without evidence of acute infarction" (Albers GW et al. [2002] N Engl J Med 21: 1713–1716). On the basis of this definition, the term 'stroke' is appropriate for an ischemic episode that results in cerebral infarction, regardless of duration.
This new definition has been endorsed and accepted by many cerebrovascular experts and incorporated into the study design of several major clinical trials. Others, however, have questioned the value of the new definition and raised multiple concerns. A common criticism involves the phrase "typically lasting less than one hour", as it is estimated that about 20% of TIAs last longer than 1 h. Another issue is that currently there is no well-accepted and widely available gold standard for documenting small brain infarctions. Some experts have suggested that episodes of brief duration (