Types of Stroke: Ischemic Stroke

What causes an ischemic stroke?
There are two types of ischemic stroke, each with a slightly different cause. The first type, thrombotic ischemic stroke, happens when a thrombus, or blood clot, slowly forms inside one of the arteries that feeds the brain. As the thrombus gets bigger, it eventually fills up the artery and keeps any blood from getting through. When blood can’t get through to the brain, an ischemic stroke happens.

The second type, embolic ischemic stroke, happens when an embolus, or floating blood clot, suddenly breaks off from a different part of the body, floats through the blood, and gets stuck in one of the arteries feeding the brain. When the embolus gets stuck in one of those arteries, blood can’t get through, and ischemic stroke happens.

What makes a thrombus form?
A thrombus is a blood clot that gradually forms over time and fills up a blood vessel. A healthy body has ways to prevent these kinds of clots from forming. In children with some illnesses, the body isn’t as good at preventing blood clots. These children can be at risk for thrombotic stroke. There are three major problems that can make clots form more easily. Most children with stroke have one or two of these problems. Some have all three; some have none. Your doctor will tell you which of the following problems may have been a factor in your child’s stroke.

Problem #1: “Thick” Blood Usually, blood cells flow freely through arteries to carry oxygen and nutrients to every part of the body. However, these blood cells also must be able to clump together and form a clot if we are injured. This is what happens when a scab forms over a cut. The body has a very complicated system that tells the blood when to flow and when to clump together and clot. In most people, this system keeps the blood flowing freely, and only allows clots to form when we need them. Some children have illnesses that affect their bodies’ ability to control when and where clots form. In these children, clots sometimes form where they are not needed. If this happens in one of the arteries that feeds the brain, it can cause an ischemic stroke.

Problem #2: Narrow Arteries Normally, blood cells flow through wide arteries that give them lots of room to move. It would take a very big clot to fill up a normal artery. Since big clots almost never form in a healthy person’s arteries, wide arteries help protect the body from blood clots that could block the flow of blood.

In a narrow artery, blood cells have much less room to move. If a tiny clot stuck to the inside wall of the artery starts to grow, it can easily fill up the narrow artery. If the clot fills up the artery, blood cannot flow and a stroke can happen.

Problem #3: “Sticky” Blood Vessels Every artery in the body has a smooth inner lining blood cells from sticking to the artery walls and forming a clot. The arrow on the left points to the smooth lining that helps protect the body from forming blood clots.

Some illnesses can damage this smooth lining. The arrow points to damaged lining that is rough and uneven. Blood cells can more easily stick to the artery walls and form a clot. If the clot is big enough to keep blood from getting through, it can cause a stroke.

Which diseases make a thrombus form?
In children, the most common illness to cause thrombotic ischemic stroke is sickle cell disease. However, there are many other illnesses that can sometimes cause thrombotic stroke. Some children are born with illnesses that can make the blood “thick” or damage the smooth lining of the arteries. Other children get illnesses when they are older, such as Systemic Lupus Erythematosus (aka “lupus”), that can damage the arteries and cause a thrombus to form. Some children with thrombotic stroke have no illnesses at all. Your doctor will tell you what illness, if any, could have played a part in causing your child’s stroke.

Next: Where does an embolus come from?

Last Updated: June 13, 2005