| Causes of
Stroke Blockage of
artery
- Clogging of arteries
within the brain (e.g.
lacunar stroke)
- Hardening of the
arteries leading to the
brain (e.g. carotid artery
occlusion)
- Embolism to the brain
from the heart or an artery
Rupture of an artery (i.e.
hemorrhage)
- Cerebral hemorrhage
(bleeding within the brain
substance)
- Subarachnoid hemorrhage
(bleeding between the brain
and the inside of the skull)
What
causes a stroke?
The blockage of an artery in the
brain by a clot (thrombosis) is
the most common cause of a
stroke. The part of the brain
that is supplied by the clotted
blood vessel is then deprived of
blood and oxygen. The cells of
that part of the brain die as a
result. Typically, a clot forms
in a small blood vessel within
the brain that has been
previously narrowed due to the
long-term, damaging effects of
high blood pressure
(hypertension) or diabetes. The
resulting strokes are called
lacunar strokes because they
look like little lakes. In other
situations, usually because of
hardening of the arteries (atherosclerosis),
a blood clot can obstruct a
larger vessel going to the
brain, such as the carotid
artery in the neck.
Another type of stroke occurs
when a blood clot or a piece of
atherosclerotic plaque
(cholesterol and calcium
deposits on the wall of the
inside of the heart or artery)
breaks loose, travels through
open arteries, and lodges in an
artery of the brain. When this
happens, the flow of oxygen-rich
blood to the brain is blocked
and a stroke occurs. This type
of stroke is referred to as an
embolic stroke. For example, a
blood clot might originally form
in the heart chamber as a result
of an irregular heart rhythm,
such as occurs in atrial
fibrillation. Usually, these
clots remain attached to the
inner lining of the heart, but
occasionally they can break off,
travel through the blood stream,
form a plug (embolism) in a
brain artery, and cause a
stroke. An embolism can also
originate in a large artery (for
example, the carotid artery, a
major artery in the neck that
supplies blood to the brain) and
then travel downstream to clog a
small artery within the brain.
A cerebral hemorrhage occurs
when a blood vessel in the brain
bursts and bleeds into the
surrounding brain tissue. A
cerebral hemorrhage (bleeding in
the brain) can cause a stroke by
depriving blood and oxygen to
parts of the brain. The
accumulation of blood from a
cerebral hemorrhage can also
press on parts of the brain and
cause damage. A subarachnoid
hemorrhage is caused by the
rupture of a blood vessel that
is usually located between the
outside of the brain and the
inside of the skull. The blood
vessel at the point of rupture
is often previously abnormal,
such as from an aneurysm (an
abnormal ballooning out of the
wall of the vessel).
Subarachnoid hemorrhages usually
cause a sudden, severe headache
and are often complicated by
further neurological problems,
such as paralysis, coma, and
even death.
Overall, the most common risk
factors for stroke are high
blood pressure and increasing
age. Diabetes and certain heart
conditions, such as atrial
fibrillation, are other common
risk factors. When strokes occur
in younger individuals (less
than 50 years old), less common
risk factors are often involved.
These risk factors include
drugs, such as cocaine or
amphetamines, ruptured
aneurysms, and inherited
(genetic) predispositions to
blood clotting. Another example
of a genetic predisposition to
stroke occurs in a rare
condition called homocystinuria,
in which there are excessive
levels of the chemical
homocystine in the body.
Furthermore, scientists are
trying to determine whether the
non-hereditary occurrence of
high levels of homocystine at
any age can predispose to
stroke. Another rare cause of
stroke is vasculitis, a
condition in which the blood
vessels become inflamed.
Finally, there appears to be a
very slight increased occurrence
of stroke in people with
migraine headache.
What is a TIA?
A transient
ischemic attack
(TIA) is a
short-lived
episode (less
than 24 hours)
of temporary
impairment to
the brain that
is caused by a
loss of blood
supply. A TIA
causes a loss of
function in the
area of the body
that is
controlled by
the portion of
the brain
affected. The
loss of blood
supply to the
brain is most
often caused by
a clot that
spontaneously
forms in a blood
vessel within
the brain
(thrombosis).
However, it can
also result from
a clot that
forms elsewhere
in the body,
dislodges from
that location,
and travels to
lodge in an
artery of the
brain (emboli).
A spasm and,
rarely, a bleed
are other causes
of a TIA. Many
people refer to
a TIA as a
"mini-stroke."
Some TIAs
develop slowly
while others
develop rapidly.
By definition,
all TIAs resolve
within 24 hours.
Strokes take
longer to
resolve than
TIAs and reflect
a more permanent
and serious
problem.
Although TIAs
often last only
a few minutes
and then end,
most experts
believe TIAs
should be
evaluated with
the same urgency
as a stroke in
an effort to
prevent
recurrences
and/or strokes.
TIAs can occur
once, multiple
times, or
precede a
permanent
stroke.
A TIA from a
clot to the eye
can cause
temporary visual
loss, which is
often described
as a curtain
coming down. A
TIA that
involves the
carotid artery
(the largest
blood vessel
supplying the
brain) can
produce problems
with movement or
sensation on one
side of the
body, which is
the side
opposite to the
actual blockage.
An affected
patient may
experience
paralysis of the
arm, leg, and
face, all on one
side. Double
vision,
dizziness
(vertigo) and
loss of speech,
understanding,
and balance can
also be symptoms
depending on
what part of the
brain is lacking
blood supply.
TIAs are
often warnings
of an impending,
more severe or
permanent stroke
and must be
immediately
evaluated by a
physician. TIAs
can reflect a
local problem in
the brain, a
plugging of the
arteries to the
brain such as
the carotid
arteries, or
they can reflect
a heart problem
in which clots
dislodge and
flow into the
brain. Examples
of these heart
conditions
include atrial
fibrillation,
valve problems,
and poorly
beating or weak
heart walls.
TIAs and
hardening of the
heart arteries
can occur
together and can
reflect an
underlying
disease such as
diabetes
mellitus, high
cholesterol, or
high blood
pressure
(hypertension).
What is the impact of strokes?
In the United States, about 400,000 people a year suffer from a stroke, and up to 40% of these strokes may be fatal. The cost of strokes is not just measured in the billions of dollars lost in work, hospitalization, and the care of survivors in nursing homes. The major cost or impact of a stroke is the loss of independence that occurs in 30% of the survivors. What was a self-sustaining and enjoyable lifestyle may lose most of its quality after a stroke and other family members can find themselves in a new role as caregivers.How is a stroke recognized?
When brain cells are deprived of oxygen, they cease to perform their usual tasks. The symptoms that follow a stroke depend on the area of the brain that has been affected and the amount of brain tissue damage.
Small strokes may not cause any symptoms, but still damage brain tissue. These strokes that do not cause symptoms are referred to as silent strokes. The most common symptom of a stroke is weakness or paralysis on one side of the body or the other. There may be a partial or complete loss of voluntary movement and/or sensation in a leg and/or arm. A stroke can cause speech problems and weak muscles of the face, which can cause drooling. Numbness or tingling in the leg, arm, or face is very common. A stroke involving the base of the brain can affect balance, vision, and swallowing functions. A stroke can cause difficulty breathing and even unconsciousness.
What should be done if you suspect you or someone else is having a stroke?
If any of the symptoms mentioned above suddenly appear, emergency medical attention should be sought. The sooner treatment is started, the better the eventual outcome will be. Therefore, the first action should be to call 911 (or whatever number activates the emergency medical response in your area). The family doctor and/or neurologist should also be contacted. However, the first priority is ensuring that the ambulance arrives as soon as possible. The affected person should lie flat to promote an optimal blood flow to the brain. If drowsiness, unresponsiveness, or nausea are present, the person should lie on one side to prevent choking on his/her vomit. Although aspirin plays a major role in stroke prevention (see below), once the symptoms of a stroke begin, it is generally recommended that additional aspirin not be taken until the patient receives medical attention. If stroke is of the bleeding type, aspirin could theoretically make matters worse. |
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http://www.medicinenet.com/stroke/article.htm |
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