Types
of Stroke
Strokes
can be classified into two main categories:
- 88 percent are ischemic
strokes - strokes caused by blockage of an artery.
- 12 percent are hemorrhagic
strokes - strokes caused by bleeding.
An ischemic
stroke occurs when a blood vessel that supplies
the brain becomes blocked or "clogged" and impairs
blood flow to part of the brain. The brain cells
and tissues begin to die within minutes from lack
of oxygen and nutrients. The area of tissue death
is called an infarct. About 80 percent of strokes
fall into this category. Ischemic strokes are
further divided into two groups, including the
following:
- thrombotic strokes
- caused by a blood clot that develops in the
blood vessels inside the brain.
- embolic strokes -
caused by a blood clot or plaque debris that
develops elsewhere in the body and then travels
to one of the blood vessels in the brain via
the bloodstream.
Thrombotic
strokes are strokes caused by a thrombus (blood
clot) that develops in the arteries supplying
blood to the brain. This type of stroke is usually
seen in older persons, especially those with high-cholesterol
levels and atherosclerosis (a build-up of fat
and lipids inside the walls of blood vessels).
Sometimes,
symptoms of a thrombotic stroke can occur suddenly
and often during sleep or in the early morning.
At other times, it may occur gradually over a
period of hours or even days. This is called a
stroke-in-evolution.
Thrombotic
strokes may be preceded by one or more "mini-strokes,"
called transient ischemic attacks, or TIAs. TIAs
may last for a few minutes or up to 24 hours,
and are often a warning sign that a stroke may
occur. Although usually mild and transient, the
symptoms caused by a TIA are similar to those
caused by a stroke.
Another
type of stroke that occurs in the small blood
vessels in the brain is called a lacunar infarct.
The word lacunar comes from the Latin word meaning
"hole" or "cavity." Lacunar infarctions are often
found in people who have diabetes or hypertension
(high blood pressure).
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.
Hemorrhagic
strokes occur when a blood vessel that supplies
the brain ruptures and bleeds. When an artery
bleeds into the brain, brain cells and tissues
do not receive oxygen and nutrients. In addition,
pressure builds up in surrounding tissues and
irritation and swelling occur. About 20 percent
of strokes are caused by hemorrhage. Hemorrhagic
strokes are divided into two main categories,
including the following:
- intracerebral hemorrhage
- bleeding from the blood vessels within the
brain.
- subarachnoid hemorrhage
- bleeding in the subarachnoid space (the space
between the brain and the membranes that cover
the brain).
Intracerebral
hemorrhage is usually caused by hypertension (high
blood pressure), and bleeding occurs suddenly
and rapidly. There are usually no warning signs
and bleeding can be severe enough to cause coma
or death.
Subarachnoid
hemorrhage results when bleeding occurs between
the brain and the meninges (the membranes that
covers the brain) in the subarachnoid space. This
type of hemorrhage is often due to an aneurysm
or an arteriovenous malformation (AVM).
- An aneurysm is a weakened,
ballooned area on an artery wall and has a risk
for rupturing. Aneurysms may be congenital (present
at birth), or may develop later in life due
to such factors as hypertension or atherosclerosis
- An AVM is a congenital
disorder that consists of a disorderly tangled
web of arteries and veins. The cause of AVM
is unknown.
Recurrent
strokes occur in about 25 percent of stroke victims
within five years after a first stroke. The risk
is greatest right after a stroke and decreases
over time. The likelihood of severe disability
and death increases with each recurrent stroke.
About 3 percent of stroke patients have a second
stroke within 30 days of their first stroke, and
about one-third have a second stroke within two
years.
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