A brain attack, or stroke, can occur when blood flow to part of the brain is interrupted in a way that injures or kills brain cells.

The term brain attack is often used to describe a stroke. Just as a heart attack happens when blood flow to the heart is interrupted, a brain attack can occur when blood flow to part of the brain is interrupted in a way that injures or kills brain cells. There are three ways this can happen:

1. A blood vessel can become blocked.
2. Blood pressure can suddenly drop.
3. A blood vessel in the brain can burst.

The way blood flow to the brain is interrupted defines the two major types of stroke: ischemic and hemorrhagic.

What Is an Ischemic Stroke?

About 87 percent of all strokes are ischemic. These strokes most often occur when an artery bringing blood to the brain becomes blocked, stopping blood flow. Less frequently, a severe drop in blood pressure causes an ischemic stroke.

Brain cells (neurons) rely on a constant stream of blood supplying oxygen and nutrients to operate normally. When blood flow is interrupted for more than a few seconds, the neurons begin to malfunction. If blood flow is not restored quickly, the neurons begin to die. This is why immediate medical evaluation and treatment is absolutely essential for people who are experiencing symptoms of a stroke.

There are two types of ischemic strokes:

Embolic Stroke

Many people wonder, “What is an embolism?” Sometimes a clot that develops elsewhere in the body—typically the heart, aorta, or carotid arteries in the neck—breaks off and travels in the bloodstream to the brain. This type of clot is called an embolus. When an embolus lodges in a brain artery, stopping blood flow, it produces an embolism that causes an embolic stroke. In addition to a blood clot, an embolus can be an air bubble or piece of debris.

Thrombotic Stroke

When a clot (thrombus) develops in a narrowed part of an artery—typically from fatty buildup in the arteries (atherosclerosis) of the brain or neck—the result is a thrombotic stroke. This type of stroke comprises about 50 percent of all strokes. A thrombotic stroke is further differentiated as a large-vessel or small-vessel thrombosis, depending on the size of the artery in which the thrombus occurs. A small-vessel thrombotic stroke deep within the brain is also called a lacunar stroke.

How Ischemic Strokes Are Categorized

Ischemic strokes are categorized according to the severity and duration of symptoms:

• Transient ischemic attack (TIA). A TIA is a sudden, transient episode of neurological dysfunction caused by lack of blood flow to part of the brain. A TIA is sometimes called a mini stroke, but it is actually a transient stroke, because it passes without causing permanent damage to the brain. TIAs typically last no more than 20 minutes or so. Since it is difficult to tell the difference between a stroke and a TIA until the TIA resolves, it’s wisest to treat a TIA as a medical emergency by calling 911.
• Progressing or evolving stroke. This is a stroke in the process of occurring. The sooner you get to an emergency department for stabilization and treatment, the better your outcome will be. If the stroke is treated quickly, you may have no lasting deficit or disability.
• Completed stroke. This is a cerebral infarction, and it means the stroke was severe enough and lasted long enough to kill a portion of brain tissue. Irreversible deficit, disability or death is likely.

What Is a Hemorrhagic Stroke

When a weakened artery in the brain ruptures, the result is a hemorrhagic stroke. Blood flowing into the brain compresses the tissue and kills brain cells.

About 75 percent of hemorrhagic strokes (13 percent of all strokes) occur within the brain itself. These are called intracerebral hemorrhages.

In the other 25 percent, the bleeding occurs in the space between the brain and the skull. These are known as subarachnoid hemorrhages.

The most common cause of a spontaneous subarachnoid hemorrhage is a ruptured aneurysm, a balloon-like outpouching from the wall of an artery,

Brain Attack Prognosis

The extent of your disability (if any) will be determined after the brain attack has ended and your condition has been stabilized. The length of time you will need to recover from a brain attack will depend on its severity. Fortunately, about 50 to 70 percent of stroke survivors are able to regain functional independence. Others are permanently disabled to various degrees.

The risk of death varies with the type of stroke and increases with age. About 40 percent of intracerebral hemorrhages cause death. About 10 to 15 percent of people who suffer a subarachnoid hemorrhage die before reaching the hospital; 40 percent die within the first week; and 50 percent die within the first six months.

With ischemic stroke, about 9 percent of patients aged 65 to 74, 13 percent of patients aged 74 to 84, and 23 percent of patients age 84 and older die within 30 days.