Understanding the different types of "brain attack"

A network of large and small blood vessels deliver oxygen and nutrients throughout your brain. If something disrupts that blood supply, brain cells begin to die. The resulting injury — known as a stroke — may be so small that it goes unnoticed. Other times, the damage is so extensive, the consequences include devastating physical and mental challenges.

Recognizing the warning signs of a stroke and taking action can be lifesaving (learn how from the American Stroke Association). But being aware of the different types and causes of strokes may help you fine-tune your efforts to prevent them in the first place.

You may have heard a stroke referred to as a brain attack. "It's not a bad term to use, because the word 'attack' conveys the urgency and importance of timely action," says Dr. Alexis Roy, acute stroke director at Harvard­affiliated Brigham and Women's Hospital. When talking to her patients, though, she prefers to describe strokes according to their underlying causes, which fall into two main categories: ischemic and hemorrhagic.

Ischemic strokes — which result from a blockage inside one of the brain's arteries — are by far the most common, accounting for 87% of all strokes. Three common subtypes of ischemic stroke are described below. Hemorrhagic strokes, also known as bleeding strokes, usually result from a ruptured blood vessel (see "What is a hemorrhagic stroke?").

Large-artery atherothrombotic stroke

These strokes occur when a blood clot forms in one of the large arteries supplying blood to the brain, usually due to a buildup of fatty plaque (atherosclerosis). Most commonly, the plaque ruptures and a clot forms on the surface. The clot then breaks loose, travels to a narrower part of an artery, and gets stuck, cutting off the blood supply. "The carotid arteries, which run up both sides of the neck, are a common location for the plaque buildup that leads to these strokes," says Dr. Roy. The large arteries that branch out from the base of the skull are another frequent site.

The atherosclerosis responsible for these strokes can also accumulate in the heart's arteries, raising the risk of heart attacks. That's why same healthy lifestyle habits endorsed by the American Heart Association can reduce your risk of both serious conditions. For anyone who's already had a heart attack, taking a daily low-dose aspirin (if your doctor recommends that) may help prevent both strokes and subsequent heart attacks.

Cardioembolic stroke

These strokes occur when a clot that has formed in the heart travels through the bloodstream until it lodges in an artery to the brain. One prime cause of embolic stroke is atrial fibrillation (afib), which affects about one in 15 people ages 65 and older. During afib, the heart's upper chambers (atria) quiver rapidly instead of contracting forcefully, leading some blood to linger in a chamber instead of flowing smoothly through the heart. Blood most commonly pools within a tiny, pouchlike extension called the left atrial appendage, eventually forming clots that may break free and move out of the heart up to the brain.

Strokes caused by afib are among the most serious because the clots that form inside the heart tend to be large and to lodge in larger brain arteries. That translates to a bigger area of brain cell damage, Dr. Roy explains. It's why most people with afib need a clot-prevention drug, such as apixaban (Eliquis) or rivaroxaban (Xarelto).

Small-vessel strokes

Although larger strokes tend to correlate with worse outcomes, the location also matters. "Some small-vessel strokes cause very little damage — only about a half-inch in diameter. But if it affects an area critical for movement, a person might lose function on one side of their body, leaving them unable to walk," says Dr. Roy. This unpredictability is one reason many people find strokes so confusing, she adds.

In fact, you can also have a "silent" ischemic stroke. It causes no noticeable symptoms because the damaged area is small and occurs in a part of the brain that doesn't control any vital functions. However, these small-vessel strokes sometimes cause temporary balance problems or clumsiness in an arm or leg that people may attribute to another cause. And if people accumulate a number of silent strokes, the damage can manifest as memory lapses and other cognitive problems. Over time, these problems may evolve into vascular dementia, the second most common form of dementia after Alzheimer's disease.