Stroke Causes and Risk Factors

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Strokes are caused by blocked blood flow to the brain (ischemic stroke) or sudden bleeding in the brain (hemorrhagic stroke). Many things raise your risk of stroke. Some of these risk factors can be changed to help prevent a stroke or future strokes.

Ischemic stroke

About 87% of strokes are ischemic. The blockage in the brain is usually caused by a piece of plaque or a blood clot. If the blockage occurs locally in the brain, the condition is called thrombosis. If the blood clot travels from somewhere else in the body, it is called an embolism. Ischemic strokes are classified specifically based on where in the brain the blockage occurs and where in the body an embolism developed. In some cases, the location of the original embolism is not known.

When plaque builds up on the inner walls of the arteries, it can lead to a disease called atherosclerosis. Plaque hardens and narrows the arteries, limiting blood flow to tissues and organs. Plaque can build up in any artery in the body, including arteries in the brain and neck. Carotid artery disease occurs when plaque builds up in the carotid arteries in the neck that supply blood to the brain. It is a common cause of ischemic stroke.

Plaque in an artery can also break open. Blood platelets stick to the site of the plaque injury and clump together to form blood clots. These clots can partly or fully block an artery.

Blood clots leading to stroke can happen when there are other heart and blood conditions, such as atrial fibrillation and sickle cell disease. MRI studies show that as many as 40% of children with sickle cell disease have had a stroke, even though a medical exam does not show signs of one. The only treatment for these undetected strokes (also called silent infarcts) is to receive regular blood transfusions.

Studies have found ischemic stroke in people who have COVID-19. However, it is too early to tell whether COVID-19 can cause stroke.

Inflammation

Chronic (long-term) inflammation contributes to ischemic stroke. Researchers are still trying to understand this fully. Research shows that inflammation can damage the blood vessels and contribute to atherosclerosis. Ischemic stroke can also lead to inflammation that further damages brain cells.

Transient ischemic attack

A transient ischemic attack (TIA) is caused by a blockage in the brain just like an ischemic stroke. With a TIA, the blockage breaks up before there is any damage to your brain. It typically lasts less than an hour but can come and go. Eventually, it can become a full stroke. A TIA is also called a mini-stroke. If you are diagnosed with a TIA in an emergency room, you should follow up as soon as possible with a primary care provider and a neurologist, a doctor who specializes in treating disorders of the brain, spinal cord, and nervous system.

Hemorrhagic stroke

Sudden bleeding can cause a hemorrhagic stroke. This can happen when an artery in or on top of the brain breaks open. The leaked blood causes the brain to swell, raising pressure in the brain that can damage brain cells. There are two types of hemorrhagic stroke: intracranial hemorrhage, or bleeding within the skull, and subarachnoid hemorrhage (SAH), or bleeding between the brain and the membrane that surrounds it. Intracranial hemorrhage occurs in about 10% of stroke cases, and SAH occurs in about 3%.

Some conditions make blood vessels in the brain more likely to bleed.

• Aneurysm is a balloon-like bulge in an artery that can stretch and burst.
• Arteriovenous malformations (AVMs) are tangles of poorly formed arteries and veins that can break open in the brain.
• High blood pressure puts pressure on the inside walls of the arteries. This pressure makes them more likely to break open, especially if they are weakened from an aneurysm or AVM.

There are many risk factors for stroke. You can treat or control some but not all of them.

Factors that you can control account for 82% to 90% of all strokes:

• High blood pressure
• Obesity
• Physical inactivity
• Poor diet
• Smoking

Ischemic and hemorrhagic strokes share many of the same risk factors, such as high blood pressure, diabetes, and high blood cholesterol. Other risk factors are specific to the type of stroke. Blood clots can arise from coronary heart disease, atrial fibrillation, heart valve disease, and carotid artery disease. Bleeding can occur after taking blood thinners.

Other risk factors are based on lifestyle, genetic , and environment.

• Age is a risk factor, too. A stroke can occur at any age, but the risk is higher for babies under the age of 1 and for adults as they grow older.
• Anxiety, depression, and high stress levels, as well as working long hours and not having much contact with family, friends, or others outside the home, may raise your risk for stroke.
• Family history and genetic play a role as well. Your risk of having a stroke is higher if a parent or other family member has had a stroke, particularly at a younger age. Certain genes affect your stroke risk, including those that determine your blood type. People with blood type AB (which is not common) have a higher risk.
• Living or working in areas with air pollution can also contribute to stroke risk.
• Other medical conditions, such as sleep apnea, kidney disease, and migraine headaches, are also factors.
• Other unhealthy lifestyle habits, including drinking too much alcohol, getting too much sleep (more than 9 hours), and using illegal drugs such as cocaine, may raise stroke risk.
• Race and ethnicity is another factor. In the United States, stroke occurs more often in Black, Alaska Native, American Indian, and Hispanic adults than in white adults.
• Sex can play a role in risk for stroke. At younger ages, men are more likely than women to have a stroke. But women tend to live longer, so their lifetime risk of having a stroke is higher. Women who take birth control pills or use hormone replacement therapy are at higher risk. Women are also at higher risk during pregnancy and in the weeks after giving birth. High blood pressure during pregnancy — such as from preeclampsia — raises the risk of stroke later in life.
• Viral infections or conditions, such as lupus or rheumatoid arthritis, can cause inflammation.