The symptoms of brain ischemia may be transient, lasting seconds to minutes, or can persist for longer periods of time. Symptoms and signs remain indefinitely if the brain becomes irreversibly damaged and infarction occurs. Unfortunately, neurologic symptoms do not accurately reflect the presence or absence of infarction, and the tempo of the symptoms does not indicate the cause of the ischemia [1,2]. This is a critical issue because treatment depends upon accurately identifying the cause of symptoms, and the nature, location, and severity of causative cardiac, hematologic, and cerebrovascular abnormalities.
The differential diagnosis of transient ischemic attack and stroke will be reviewed here. The evaluation of stroke and transient cerebral ischemia are discussed separately. (See "Overview of the evaluation of stroke" and "Initial evaluation and management of transient ischemic attack and minor stroke".)
TRANSIENT ISCHEMIC ATTACK
Transient ischemic attack (TIA) is defined as a transient episode of neurologic dysfunction caused by focal brain, spinal cord, or retinal ischemia, without acute infarction. In keeping with this definition of TIA, ischemic stroke is defined as an infarction of central nervous system tissue. (See "Definition of transient ischemic attack".)
The term "transient ischemic attack" was first introduced in the early 1950s based upon the recognition that a transient focal loss of neurologic function often preceded strokes . In the years after this initial description in patients with carotid artery disease, various groups and committees arbitrarily defined TIAs as lasting less than 24 hours . However, this classic definition of TIA was inadequate for several reasons. Most notably, there is risk of permanent tissue injury (ie, infarction) even when focal transient neurologic symptoms last less than one hour.
Subsequent data demonstrated that ischemic attacks that last longer than one hour are most often associated with brain infarction [4,5]. Most TIAs last less than one hour . Thus, the benign connotation of TIA has been replaced by an understanding that even relatively brief ischemia can cause permanent brain injury.