Watershed Stroke

Watershed strokes: named for affecting the watershed areas of the brain.

Carotid stenosis is a precipitating factor in watershed strokes
Photo © A.D.A.M.

A watershed stroke is named that way because it affects the watershed areas of the brain. These areas are thin strips of brain which are sandwiched in between the farthest end branches of two adjacent vascular territories. Because these are the farthest tissues supplied by an artery, adequate blood pressure must be maintained to ensure that enough blood is pumped into these areas.

What is Stroke?

Stroke is a disease that affects the arteries leading to and within the brain.

It is the No. 5 cause of death and a leading cause of disability in the United States. A stroke occurs when a blood vessel that carries oxygen and nutrients to the brain is either blocked by a clot or bursts (or ruptures). When that happens, part of the brain cannot get the blood (and oxygen) it needs, so it and brain cells die.

Effects of Stroke

The brain is an extremely complex organ that controls various body functions.  If a stroke occurs and blood flow can't reach the region that controls a particular body function, that part of the body won't work as it should. 

Risk Factors of Stroke

  • Age — The chance of having a stroke approximately doubles for each decade of life after age 55. While stroke is common among the elderly, a lot of people under 65 also have strokes.
  • Heredity (family history) — Your stroke risk may be greater if a parent, grandparent, sister or brother has had a stroke. 
  • Race — African-Americans have a much higher risk of death from a stroke than Caucasians do. This is partly because blacks have higher risks of high blood pressure, diabetes and obesity.
  • Sex (gender) — Each year, women have more strokes than men, and stroke kills more women than men. Use of birth control pills, pregnancy, history of preeclampsia/eclampsia or gestational diabetes, oral contraceptive use, and smoking, and post-menopausal hormone therapy may pose special stroke risks for women. 
  • Prior stroke, TIA or heart attack — The risk of stroke for someone who has already had one is many times that of a person who has not. Transient ischemic attacks are "warning strokes" that produce stroke-like symptoms but no lasting damage. TIAs are strong predictors of stroke. A person who's had one or more TIAs is almost 10 times more likely to have a stroke than someone of the same age and sex who hasn't. Recognizing and treating TIAs can reduce your risk of a major stroke. TIA should be considered a medical emergency and followed up immediately with a healthcare professional. If you've had a heart attack, you're at higher risk of having a stroke, too.

Watershed Strokes

Watershed areas are at high risk of developing ischemia, or lack of blood flow, during extreme drops of blood pressure. Common triggers for watershed strokes include periods of extreme dehydration, heart attacks, and sepsis (widespread infections). If ischemia to watershed areas is maintained longer than a few minutes the tissues in watershed areas begin to die, causing a stroke.

Watershed areas are particularly vulnerable to low blood pressure in people who have advanced carotid stenosis.

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