Strokes are either:
Ischemic. These are strokes caused by the blockage of an artery (or rarely, a vein). Most strokes are this type.
Hemorrhagic. These are strokes caused by bleeding. About 13 in 100 strokes are this type.
An ischemic stroke occurs when a blood vessel that supplies the brain becomes blocked. This affects blood flow to part of the brain. The brain cells and tissues start to die within minutes from lack of oxygen and nutrients. Ischemic strokes are further divided into 2 groups:
Thrombotic strokes. These are caused by a blood clot that develops in the blood vessels inside the brain.
Embolic strokes. These are caused by a blood clot that develops elsewhere in the body. The clot then travels to 1 of the blood vessels in the brain through the bloodstream.
Thrombotic strokes are strokes caused by a blood clot (thrombus) that develops in the arteries supplying blood to the brain. This type of stroke is usually seen in older people, especially those with diabetes or high cholesterol and a buildup of fat and lipids inside the walls of blood vessels (atherosclerosis).
Sometimes, symptoms of a thrombotic stroke can occur suddenly. They can happen during sleep or in the early morning. At other times, it may occur gradually over a period of hours or even days.
Mini-strokes are also called transient ischemic attacks (TIAs). One of more of these may happen before a thrombotic stroke. TIAs may last for a few minutes or up to 24 hours. They are often a warning sign that a stroke may occur. Symptoms of a TIA are often mild and temporary, but they are similar to those caused by a stroke.
Another type of ischemic stroke that occurs in the deep penetrating branches of the small blood vessels in the brain is called a lacunar infarct. The word lacunar comes from the Latin word meaning "hole" or "cavity." Lacunar infarctions are often found in people who have diabetes or high blood pressure.
Embolic strokes are usually caused by a blood clot that forms elsewhere in the body (embolus) and travels through the bloodstream to the brain. Embolic strokes are often caused by heart disease or heart surgery. They happen quickly and without any warning signs. About 3 in 20 embolic strokes occur in people with atrial fibrillation. This is a type of abnormal heart rhythm where the upper chambers of the heart (atria) beat irregularly.
Hemorrhagic strokes occur when a blood vessel that supplies the brain ruptures and bleeds. When an artery bleeds into the brain, brain cells and tissues don't get oxygen and nutrients. Pressure also builds up in surrounding tissues and irritation and swelling occurs. This can lead to more brain damage. Hemorrhagic strokes are divided into 2 main categories:
Intracerebral hemorrhage. Bleeding is from the blood vessels within the brain.
Subarachnoid hemorrhage. Bleeding is in the space between the brain and the membranes that cover the brain (subarachnoid space).
Intracerebral hemorrhage is usually caused by high blood pressure. Bleeding occurs quickly. There are usually no warning signs. Bleeding can be severe enough to cause coma or death.
Subarachnoid hemorrhage results when bleeding occurs between the brain and the membrane that covers the brain (meninges) in the subarachnoid space. This type of hemorrhage is often because of an aneurysm or an arteriovenous malformation (AVM). It can also be caused by trauma.
An aneurysm is a weakened, ballooned area on an artery wall. It may break (rupture). Aneurysms may be present at birth (congenital) or develop later in life because of high blood pressure or blood vessel disease (atherosclerosis).
An AVM is a congenital problem that has a disorderly tangled web of arteries and veins. The cause of AVM is unknown. It's sometimes genetic or part of certain syndromes.
Recurrent strokes occur in about 1 in 4 people who have had a stroke. They happen within 5 years after a first stroke. The risk is greatest right after a stroke and decreases over time. The likelihood of severe disability and death increases with each recurrent stroke. About 3 in 100 people who have had a stroke have a second stroke within 30 days of their first stroke. About one-third have a second stroke within 2 years.