Cerebral ischemia results from interference with blood circulation to the brain. The ischemic event can occur as a result of intrinsic vessel pathology that leads to thrombosis; embolic phenomena; or systemic hypoperfusion. Cerebral circulation is usually maintained by a very efficient collateral arterial system that includes the 2 carotid and the 2 vertebral arteries, anastomoses in the circle of Willis, and collateral circulation in the cerebral hemispheres. However, atheromas and congenital arteriovenous malformations (AVMs) can lead to a reduction in cerebral blood flow. This reduction may be generalized or localized. Interruptions in cerebral blood flow can result in permanent neurologic deficits, depending on the extent and duration of the cerebral ischemia.
Transient Cerebral Ischemia
Transient cerebral ischemia (TCI) is now defined as a transient episode of neurologic dysfunction caused by focal ischemia without infarction. The previous, time-based definition of TCI (formerly referred to as a transient ischemic attack), which described the episode as a sudden-onset focal loss of neurologic function, persisting for less than 24 hours, is inadequate; infarction can occur even after a brief period of ischemia, even if the presenting focal neurologic symptoms resolve in less than 1 hour. The new term TCI, with its tissue-based definition, more accurately reflects its pathophysiology and encourages the use of diagnostic testing to identify evidence of permanent tissue injury. The presence of acute infarction is a strong predictor of a recurrent ischemic stroke. The occurrence of TCI is not only an important prognostic indicator for a future stroke but is also associated with a rising mortality over time. Most TCIs last only a few minutes, and the symptoms are primarily associated with insufficiency of the internal carotid, middle cerebral, or vertebrobasilar arterial territories.
Excerpted from BCSC 2020-2021 series: Section 1 - Update on General Medicine. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.