Watershed Stroke

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A watershed stroke is given that name because it affects one or more of the regions of the brain that are called 'watershed areas.'

The watershed areas of the brain are positioned in such a way that they simultaneously receive blood supply from two separate groups of arteries. While this is perfectly fine most of the time, it can be problematic under certain circumstances, which can increase the risk of stroke.

Symptoms of Watershed Strokes

The watershed regions of the brain may be affected by an interruption of blood flow, resulting in a stroke. The symptoms of a watershed stroke include weakness and/or vision loss on the right or the left side. If a watershed stroke is caused by extremely low blood pressure or severe blood loss, the symptoms may affect the right and the left sides.

A watershed stroke can often be diagnosed through a neurological history and physical examination. A watershed stroke can be identified on a brain CT or a Brain MRI.

Causes of Watershed Strokes

Ischemic Stroke

A blood clot interrupting blood supply to a region of the brain can cause an ischemic stroke in any location of the brain, including the watershed regions. Ischemia causes an area of the brain to 'starve' from blood. Because blood provides vital nutrients and oxygen, the affected region of the brain cannot function in the setting of ischemia, which results in a stroke.

The watershed regions of brain are located at the farthest end branches of two adjacent vascular territories (arterial supply systems.) This means that two separate sets of arteries supply blood to the watershed regions. This arrangement seems like it would protect the watershed areas from ischemia, but it doesn't.

In fact, the watershed regions rely on both sets of arteries to provide adequate blood supply, so if one arterial supply system is interrupted by a blood clot, the watershed region of the brain suffers from interrupted blood flow, which results in an ischemic stroke.

Low Fluid Volume/ Low Blood Pressure

Because the watershed areas are the farthest regions supplied by arterial supply systems, adequate blood flow and blood pressure must be maintained to ensure that enough blood is pumped into these areas. Watershed areas are at high risk of developing ischemia, or lack of blood flow, during extreme drops of blood pressure. If low blood flow to watershed areas lasts for longer than a few minutes, the tissues in the watershed areas begin to die, causing a stroke due to low blood volume.

Common triggers for watershed strokes include events that affect blood supply to the brain. Heart attacks, which affect the pumping ability of the heart, potentially cause significantly diminished blood flow to the brain.

Watershed areas are particularly vulnerable to low blood pressure in people who have advanced carotid stenosis, which is narrowing of the blood vessels in the neck that carry blood to the brain.

Other conditions can cause sudden or severely low blood pressure. The conditions include severe dehydration, which results in an overall low volume of fluid in the whole body. Severe infections, such as sepsis, an infection that has spread throughout the blood stream, may cause the blood pressure to drop dramatically, potentially causing a watershed stroke. And, profuse bleeding, which may a result from major injury and trauma, can cause such a significant amount of blood loss that the brain does not receive enough blood supply to the watershed regions.

Treatment of Watershed Strokes

Like all strokes, watershed strokes require urgent medical attention. The management of watershed strokes includes close observation and careful medical management. If you have had an ischemic watershed stroke caused by a blood clot, then you should expect to receive stroke treatments focused on blood thinners and medical stabilization.

If you have had a watershed stroke as a result of severe blood loss or low blood pressure, then your treatment is more likely to be focused on maintaining an adequate fluid and blood pressure.

A Word From Verywell

A stroke is a major event that changes your life. As you recover from your stroke, you will most likely get a medical workup that identifies whether you have stroke risk factors. If you learn that you have any of the stroke risk factors, you can take steps to prevent another stroke from happening.

Sources:

Watershed infarctions are more prone than other cortical infarcts to cause early-onset seizures.Denier C, Masnou P, Mapoure Y, Souillard-Scemama R, Guedj T, Théaudin M, Fagniez O, Join-Lambert C, Lozeron P, Ducot B, Ducreux D, Adams D, Arch Neurol. 2010 Oct;67(10):1219-23

Edited by Heidi Moawad MD

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