Hello jat-ga,
You are correct, some strokes are caused by blood clots that are
formed outside of the brain.
There are two main types of stroke, ischemic and hemorrhagic.
Ischemic strokes are caused by blood clots in the brain. Hemorrhagic
strokes are caused by ruptured blood vessels bleeding into the brain.
Ischemic strokes account for 70-80 percent of all strokes. There are
two types of ischemic strokes: thrombotic and embolic.
In a thrombotic stroke, a blood clot (a thrombus) forms in an artery
in or leading to the brain, blocking the blood flow. This is the most
common type of ischemic stroke.
In an embolic stroke, a blood cot (an embolus) that forms away from
the brain, usually in the heart, is carried by the bloodstream until
it lodges in an artery leading to or in the brain, blocking the flow
of blood.
Lawrence Livermore National Laboratory
“On the Offensive Against Brain Attack”
http://www.llnl.gov/str/Fitch.html
“There are two main types of strokes, ischemic and hemorrhagic.
Clots--cerebral thrombuses or cerebral embolisms--cause ischemic
strokes. Cerebral hemorrhage or subarachnoid hemorrhage causes
hemorrhagic strokes. Ischemic strokes are the most common, hemorrhagic
strokes the most deadly.
Cerebral thrombosis occurs when a blood clot (a thrombus) forms in an
artery in or leading to the brain, blocking the blood flow. It is the
most common cause of ischemic stroke. Cerebral embolism occurs when a
wandering clot (an embolus) or some other particle occurs in a blood
vessel away from the brain, usually the heart. The clot is carried by
the bloodstream until it lodges in an artery leading to or in the
brain.
A cerebral hemorrhage occurs when an artery in the brain bursts,
flooding the surrounding tissue with blood. Bleeding from an artery in
the brain can be caused by a head injury or a burst aneurysm, a
blood-filled pouch that balloons out from a weak spot in the artery
wall. A subarachnoid hemorrhage occurs when a blood vessel on the
surface of the brain ruptures and bleeds into the space between the
brain and the skull (but not into the brain itself).”
American Heart Association
http://www.americanheart.org/presenter.jhtml?identifier=4755
“What is a cerebral embolism?
A wandering clot (an embolus) or some other particle that forms away
from the brain, usually in the heart, may cause an ischemic stroke.
The clot is carried by the bloodstream until it lodges in an artery
leading to or in the brain, blocking the flow of blood.
The most common cause of these emboli is blood clots that form during
atrial fibrillation. This is a disorder found in about 2 million
Americans. In atrial fibrillation the heart's two small upper chambers
(the atria) quiver instead of beating effectively. Some blood isn't
pumped completely out of them when the heart beats, so it pools and
clots. When a blood clot enters the circulation and lodges in a
narrowed artery of the brain, a stroke occurs.”
Stanford Hospital & Clinics
http://www.stanfordhospital.com/healthLib/atoz/cardiac/types.html
“What is an embolic stroke?
Embolic strokes are usually caused by an embolus (a blood clot that
forms elsewhere in the body and travels through the bloodstream to the
brain). Embolic strokes often result from heart disease or heart
surgery and occur rapidly and without any warning signs. About 15
percent of embolic strokes occur in people with atrial fibrillation, a
type of abnormal heart rhythm in which the upper chambers of the heart
do not beat effectively.”
Stanford University Stroke Center
http://strokecenter.stanford.edu/part1.html
“Embolic Stroke (or cerebral embolism) is also caused by a clot;
however, unlike cerebral thrombosis, the clot originates somewhere
other than the brain. Embolic stroke occurs when a piece of clot (an
embolus) breaks loose and is carried by the blood stream to the brain.
Traveling through the arteries as they branch into smaller vessels,
the clot reaches a point where it can go no further and plugs the
vessel, cutting off the blood supply. This sudden blockage is called
an embolism.
You may also hear the term cerebral infarction in connection with
these two types of stroke. An infarct is an area of necrosis, or
tissue death, due to obstruction of a blood vessel by a thrombus or
embolus. Thrombotic and embolic strokes are the two types of the
cerebral infarction category of stroke.”
Other References:
BBC News
“Heart Disease & Stroke: The Facts”
http://news.bbc.co.uk/hi/english/static/in_depth/health/2000/heart_disease/stroke.stm
National Stroke Association
Types of Stroke
http://209.107.44.93/NationalStroke/AllAboutStroke/Types+of+Stroke.htm
Neuroscience for Kids
The Blood Supply of the Brain
http://faculty.washington.edu/chudler/vessel.html
American Health Assistance Foundation
EMBOLIC STROKE
http://www.ahaf.org/hrtstrok/about/EmbolicStroke.htm
Stroke (cerebrovascular accident)
http://www.netdoctor.co.uk/diseases/facts/stroke.htm
UNIVERSITY OF MARYLAND MEDICINE
Stroke / Brain Attack
http://www.umm.edu/cardiac/stroke.htm
I hope you have found this information helpful. If you have any
questions, please request clarification prior to rating the answer.
Googlenut
Google Search Terms:
stroke "blood clot"
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"embolic stroke"
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"embolic stroke" OR embolism OR embolus brain
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"embolic stroke" percent OR percengtage
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