What is Stroke?
Stroke is the 4th leading cause of death in the United States, but the leading cause of disability.
Stroke is a brain (not heart) injury that affects the brain’s blood supply. A stroke happens when:
- A clot blocks a blood vessel in the brain (called an ischemic stroke) or
- A weakened blood vessel in or near the brain bursts and bleeds (called a hemorrhagic stroke).
Both situations interrupt blood flow, starving the area of oxygen and nutrients, and damaging brain cells. Stroke can lead to death or permanent disability.
The location of the clot or rupture determines the extent of disability or death. Stroke can occur in:
- The right or left side (hemisphere) of the cerebrum, which is the largest part of the brain, and controls functions on either side of the body, plus the ability to speak and think.
- The cerebellum, which is located in the lower, back part of the brain, and helps with body and eye movement, and balance.
- The brainstem, which is located directly above the spinal cord, and essential for controlling the body’s vital functions such as heartbeat, breathing and blood pressure.
Ischemic strokes can happen in several ways:
Thrombotic strokes – when a blood clot (thrombus) blocks an artery going to the brain. A build-up of cholesterol or fat deposits inside the blood vessel wall can produce clots, blocking blood flow and damaging brain cells. Thrombotic strokes can happen inside large blood vessels (large vessel thrombosis) or small vessels (called small vessel disease or lacunar infarction).
Embolic strokes – when a traveling clot (embolus) that is carried in the bloodstream blocks a blood vessel inside, or leading to, the brain. These clots typically form in the neck or heart arteries.
Hypoperfusion (or low blood flow) strokes – when not enough blood reaches the brain because of a heart attack or low blood pressure. This type of stroke occurs when the heart cannot pump enough blood to the brain, especially if one of the arteries that supply the brain is narrowed because of cholesterol build-up.
TIAs, or transient ischemic attacks – when the blood supply to a part of the brain is briefly interrupted. A TIA is considered a “warning symptom” or “minor” stroke with symptoms that generally last a few minutes. No stroke is minor, though. TIAs are often risk factors for major strokes to follow, and require immediate medical attention.
There are two types of hemorrhagic, or bleeding-related, strokes:
Intracerebral hemorrhages – when a blood vessel bursts or bleeds, and floods brain tissue located inside the brain. Aging blood vessels or high blood pressure is often the cause. Another trigger is vascular malformations – a group of abnormal blood vessels in the brain. A rupture in one of these vessels can lead to a brain bleed.
Subarachnoid hemorrhages – when an aneurysm that is near or on the brain’s surface bursts and leaks into the area between the skull and the brain. An aneurysm is a blood-filled, balloon-like bulge inside an artery. High blood pressure is often the cause, but other risk factors include smoking, oral contraceptives and substance abuse.