Watershed stroke

Brain ischemia
T1 MRI of an ischemic stroke in the brain without (left) and with (right) contrast.
Classification and external resources
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Ventricles and Arteries
Schematic representation showing relations of the ventricles to the surface of the brain.
Schematic representation of the Circle of Willis, arteries of the brain and brain stem.
Anatomical terms of neuroanatomy []

Internal carotid artery
Arteries of the neck. The internal carotid arteries arise from the common carotid arteries - labeled Common caroti on the figure.
Anatomical terminology []

A watershed stroke or watershed infarct is defined as ischemia that is localized to the vulnerable border zones between the tissues supplied via the Anterior, Posterior and Middle Cerebral arteries.(Note that the actual blood stream blockage/restriction site can be located far away from the infarcts. See "Pathogenesis" followed.) Watershed locations are those border-zone regions in the brain supplied by the major cerebral arteries where blood supply is decreased. Watershed strokes are a concern because they comprise approximately 10% of all ischemic stroke cases. The watershed zones themselves are particularly susceptible to infarction from global ischemia as the distal nature of the vasculature predisposes these areas to be most sensitive to profound hypoperfusion.

Watershed strokes are localized to two primary regions of the brain, and are termed cortical watersheds (CWS) and internal watersheds (IWS). Patients with many different cardiovascular diseases have a higher likelihood of experiencing a blood clot or loss of blood flow in border-zone regions of the brain. The resulting symptoms differ based on the affected area of the brain. A CT scan and MRI are used for diagnosis, and afterward several treatment options are available, including the removal of atherosclerotic plaque and a physical widening of the clogged blood vessel. Long-term care is focused around three areas: rehabilitative therapy, surgical interventions, and prevention of future watershed strokes. Going forward, research to combat watershed strokes is focusing on various topics, such as stem cell research.

Watershed strokes are named because they affect the distal watershed areas of the brain. The original terminology came from the German literature, which used the analogy of an irrigation system. The German scholars compared the blood flow in distal arterial territories of the brain to the last field on a farm, which was the area with the least supply of water and therefore most vulnerable to any reduction in flow. In a medical context, the term "watershed" refers to those areas of the brain that receive dual blood supply from the branching ends of two large arteries.