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What Is Stroke?

Answers to 'What Is Stroke?' 'What Causes Stroke?' and More

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Updated August 03, 2009

What Is Stroke?

Carotid Plaque in Stroke

You have heard the term over and over again but you still wonder: What is stroke anyway? Stroke is a sudden impairment in brain function. One may suffer an inability to speak or speak clearly, walk, or move a limb because blood has stopped flowing to an area of the brain. Usually, this is caused by the blockage, or the rupture, of a blood vessel.

Unlike ministrokes, which are also known as transient ischemic attacks (TIA), whose symptoms resolve on their own in less than 24 hours, strokes leave behind long-lasting neurological impairments. The severity of these impairments depends on how large the damage is to the brain, and on the part of the brain that is affected.

Ministroke/TIA Basics

What Are The Different Types of Stroke?

There are two major categories of stroke: ischemic and hemorrhagic.

Ischemic Stroke

This type of stroke is caused by the physical blockage of blood flow to an area of the brain. The most common forms of ischemic stroke are:

1) Embolic Stroke
This type of stroke occurs when a blood clot or a cholesterol plaque wanders into the brain until it reaches a narrow point where it becomes trapped. This causes a blockage of the artery and prevents blood from reaching a section of the brain. There are other, less frequent causes of embolic strokes which include:


2) Thrombotic Stroke
In this type of stroke a blood clot forms along the inside of a blood vessel causing the interruption of blood flow to an area of the brain. Such a blood clot, also known as a thrombus, usually affects very small blood vessels in the brain, especially in people who have high cholesterol.

High Cholesterol Basics

Because small blood vessels in the brain bring blood to proportionally small brain areas, thrombotic strokes tend to be small, and are sometimes referred to as lacunar strokes. In some rare instances, however, a large blood clot can form inside of one the large blood vessels in the neck, and later break off causing a large embolic stroke.

Hemorrhagic Stroke

This type of stroke occurs when a blood vessel inside of the brain ruptures, allowing blood to pool inside or around healthy brain tissue. In many cases this is the result of uncontrolled high blood pressure.

High Blood Pressure Basics

Depending on the location of bleeding, a hemorrhagic stroke is further subdivided into

  • Intracerebral Hemorrhage: Bleeding takes place inside the brain tissue.
  • Subarachnoid Hemorrhage: Bleeding takes place along a space between two of the membranes that cover the brain.
  • Intraventricular Hemorrhage: Bleeding takes place inside the ventricles of the brain, which do not contain brain tissue, but instead are filled with a fluid known as cerebro-spinal fluid. Blood inside the ventricles rarely causes a stroke by itself, but it has the potential to cause hydrocephalus a condition in which elevated intracraneal pressure can cause stroke and even death.
  • Subdural Hemorrhage: Bleeding takes place outside of the brain tissue near the skull.

Hemorrhagic strokes are most often caused by a ruptured blood vessel such as an aneurysm or a leaky arteriovenous malformation (AVM). Blood inside the brain produces a very severe headache, which is typically described by people as the worst headache of their lives.

As blood accumulates in the brain, the normal brain tissues are pushed against the walls of the skull. This process increases the pressure inside the brain, to the point that blood flow to the areas of highest pressure is completely interrupted. These areas cease to function, and cause symptoms which can range from dizziness, nausea and vomiting to a headache accompanied by typical stroke symptoms. Hemorrhagic stroke symptoms should never be ignored as very often they can evolve rapidly and in the worse cases they can lead to sudden death.

Learn about the conditions that lead to stroke

Source:

Merritt's Neurology; 11th Edition, Lippincott Williams & Wilkins; pp 275-290

Recommended Reading:
What are the symptoms of a stroke?
Am I at risk of stroke?

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