A stroke occurs when blood that carries oxygen to the brain is blocked.

Stroke is a medical emergency. Without oxygen, brain cells begin to die within a few minutes.

Stroke is the fifth leading cause of death in the United States, according to the Centers of Disease Control and Prevention (CDC).

Every year, nearly 800,000 people in the United States have a stroke, roughly the same amount of people who live in San Francisco.

Strokes can occur at any age, though stroke risk increases as you get older.

Types of Stroke

There are two main types of stroke:

  • Ischemic strokes are caused by blood clots.
  • Hemorrhagic strokes are caused by bleeding in or around the brain.

Ischemic Stroke

Ischemic strokes account for 87 percent of all strokes.

They happen when there’s a blood clot that blocks blood flow to a part of the brain.

There are two ways this can happen:

  1. A clot can form in a blood vessel of the neck or brain that has been narrowed by a build-up of plaque. Plaque is a combination of fat, cholesterol and other substances that build up in the inner lining of the artery walls. This condition is often referred to as atherosclerosis, or “hardening of the arteries.”
  2. A clot can break off from a blood vessel somewhere else in the body and travel to the brain where it becomes stuck in one of the brain’s tiny blood vessels. This is called embolism.

Hemorrhagic Stroke

Hemorrhagic strokes occur when a weakened blood vessel in the brain ruptures and bleeds into surrounding brain tissue.

This puts too much pressure on blood cells in the surrounding tissue, cutting off their blood supply and causing damage.

An aneurysm — a weak spot in a blood vessel wall that balloons outward — can lead to a hemorrhagic stroke, as can a tangle of malformed blood vessels called an arteriovenous malformation.

Chronic high blood pressure may also weaken spots in the artery wall, making these spots more prone to rupture.

About 13 percent of all strokes are hemorrhagic strokes.

What Is a TIA?

A TIA, or transient ischemic attack, is a temporary blockage caused by a blood clot.

TIA is sometimes referred to as “mini stroke” or “warning stroke,” because it can be a warning sign of a future stroke.

About 40 percent of people who have a TIA will have a major stroke within a year if the condition is not treated, according to the Centers of Disease Control and Prevention (CDC).

Stroke Complications

A stroke may cause temporary or permanent disabilities.

Stroke complications will depend on what part of the brain was affected by the stroke and for how long the brain was without oxygen.

Some common stroke complications include:

  • Brain swelling
  • Difficulty talking or swallowing
  • Bladder control problems
  • Seizures
  • Depression
  • Difficulty walking or moving your limbs
  • Memory loss

Treatment for stroke complications usually involves a combination of therapy and medication.