What is a Stroke?

A stroke occurs when the blood supply to part of the brain is suddenly interrupted or when a blood vessel in the brain bursts, spilling blood into the spaces surrounding brain cells. In the same way that a person suffering a loss of blood flow to the heart is said to be having a heart attack, a person with a loss of blood flow to the brain or sudden bleeding in the brain can be said to be having a "brain attack."

Brain cells die when they no longer receive oxygen and nutrients from the blood or when they are damaged by sudden bleeding into or around the brain. Ischemia is the term used to describe the loss of oxygen and nutrients for brain cells when there is inadequate blood flow. Ischemia ultimately leads to infarction, the death of brain cells which are eventually replaced by a fluid-filled cavity (or infarct) in the injured brain.

When blood flow to the brain is interrupted, some brain cells die immediately, while others remain at risk for death. These damaged cells make up the ischemic penumbra and can linger in a compromised state for several hours. With timely treatment these cells can be saved. The ischemic penumbra is discussed in more detail in the Appendix.

Even though a stroke occurs in the unseen reaches of the brain, the symptoms of a stroke are easy to spot. Including,

• sudden numbness or weakness, especially on one side of the body
• sudden confusion or trouble speaking or understanding speech
• sudden trouble seeing in one or both eyes
• sudden trouble walking, dizziness, or loss of balance or coordination
• or sudden severe headache with no known cause.

All of the symptoms of stroke appear suddenly, and often there is more than one symptom at the same time. Therefore stroke can usually be distinguished from other causes of dizziness or headache. These symptoms may indicate that a stroke has occurred and that medical attention is needed immediately.

There are two forms of stroke: ischemic - blockage of a blood vessel supplying the brain, and hemorrhagic - bleeding into or around the brain. The following sections describe these forms in detail.

Page 02