What Is a Watershed Stroke?

A watershed stroke occurs when the blood flow to parts of the brain, known as border zones, is severely reduced, leading to brain tissue death. The border zones are vulnerable because they are situated furthest away from the three major arteries that service the brain.

A watershed stroke, also known as a border-zone infarct, is a medical emergency. It is commonly triggered by a heart attack, severe brain infections, heavy bleeding, or a steep drop in blood pressure. Though rarely fatal, watershed strokes can lead to the loss of motor control, dementia, and other neurological problems.

This article discusses the symptoms, causes, and diagnosis of watershed strokes and how they are treated based on the underlying cause.

Symptoms and Warning Signs of a Watershed Stroke

Watershed strokes are one type of ischemic stroke. Ischemic strokes are those in which the blood flow to the brain is restricted or reduced. They differ from hemorrhagic strokes in which blood vessels servicing the brain burst.

The symptoms of a watershed stroke are similar to that of other ischemic strokes. But, because it involves border zones (tissues that lie adjacent to those serviced by the main cerebral arteries), the symptoms are often milder and easily missed at first. The symptoms can also come and go.

Symptoms of a watershed stroke might include:

• Facial drooping
• Tilting of the head to one side
• Weakness or paralysis of one leg (and sometimes the arm on the same side of the body)
• Vision loss in half of the field of vision
• Slurred speech
• Seizures (which are far more common with watershed strokes)
• Mood disturbances (such as uncontrollable and inappropriate laughing or crying)
  

Causes

Ischemic strokes are characterized by the restriction or reduction of blood to the brain. This deprives the brain of the oxygen and nutrients it needs to keep regional tissues alive.

The three most common causes of a watershed include:

• Heart attack: Also known as a myocardial infarction, this can affect the heart's ability to pump an adequate blood supply to the brain. This is especially true in people with carotid artery stenosis (the narrowing of the main blood vessel that delivers blood from the heart to the brain).
• Hypovolemia: This is any condition that can cause a sudden or severe drop in blood pressure due to the loss of body fluids or blood. This includes severe dehydration and profuse bleeding.
• Sepsis: This is a severe infection that spreads into the bloodstream. Sepsis triggers an extreme inflammatory reaction that can cause the blood pressure to drop dramatically.

Risk Factors

The risk factors for a watershed stroke are the same as for any other form of ischemic stroke. They typically involve a combination of lifestyle and medical factors, such as:

• Older age
• Being overweight or obese
• An inactive lifestyle
• High blood pressure
• High cholesterol
• Excessive alcohol use
• Cigarette smoking
• Diabetes
• Obstructive sleep apnea
• A family history of stroke or heart attacks
• Having heart disease, including congestive heart failure, congenital heart defects, or atrial fibrillation
  

Diagnosis

A watershed stroke is diagnosed in the same way as any other stroke. It starts with a review of your medical history and a physical exam along with one or more imaging tests to determine the cause of your stroke.

Imaging studies used to diagnose a stroke include:

• Computed tomography (CT) scan: This technology composites multiple X-ray images to create three-dimensional "slices" of the brain. CT scans are especially good at identifying hemorrhagic stroke.
• Magnetic resonance imaging (MRI) scan: This technology creates highly detailed images of soft tissues using magnetic and radio waves. When used with a contrast dye, an MRI can locate areas of blockage or reduced blood flow in the vessels servicing the brain.
• Doppler ultrasound: This technology uses reflected sound waves to create detailed images of blood vessels and soft tissues. An ultrasound can detect strokes caused by blood clots and narrowed vessels.

Blood tests also may be ordered to check for risk factors associated with ischemic stroke, including cholesterol levels, triglyceride levels, and blood coagulation tests.

Treatment

Watershed strokes require emergency medical attention to prevent irreparable brain injury. The treatment can vary by the cause of the stroke as well as its severity.

If a watershed stroke was caused by a blood clot, you should expect to receive blood thinners to improve blood flow. You might also be a candidate for tissue plasminogen activator (TPA), an agent delivered intravenously (through a vein) to dissolve the clot.

If the obstruction is due to carotid stenosis, a surgical procedure known as carotid endarterectomy may be used to widen the carotid artery and increase blood flow.

Alternatively, the carotid artery can be accessed through percutaneous angioplasty. This involves the insertion of a tube (called a balloon catheter) that is fed to the site of obstruction and inflated to widen the vessel. A tiny mesh tube, called a stent, can then be placed in the vessel to keep it open.

If a watershed stroke was the result of severe blood loss or low blood pressure, your treatment is more likely to be focused on maintaining adequate fluid and blood pressure with intravenous (IV) fluids and/or a blood transfusion.

Prognosis

A watershed stroke is rarely fatal but can cause severe disability, particularly if it is not treated appropriately. Damage to the border zones of the brain can lead to difficulties with movement as well as speech and muscle coordination. Dementia (involving problems with thinking, remembering, learning, reasoning, or language) is also common.

With the appropriate rehabilitation (which may involve physical, occupational, speech, or language therapies), many of the abilities can be improved upon or restored. Even so, rehabilitation efforts can take time.

Summary

A watershed stroke is a type of stroke that involves tissues situated furthest away from the main arteries of the brain. Symptoms are similar to other types of stroke, although they are often milder and easily missed at first. Even so, a watershed stroke can lead to severe disability, including dementia and the loss of motor function, if not diagnosed and treated promptly.

A Word From Verywell

A stroke is a major event that can change your life. As you recover, you will most likely get a medical workup to identify whether you have ongoing risk factors for stroke. This is important because having a stroke places you at risk of having another one.

By taking preventive steps, such as quitting cigarettes, taking blood thinners, and exercising regularly, you can better ensure that your first stroke is your last.