There are two main types of stroke — ischemic and
hemorrhagic. Ischemic stroke is more common and occurs
when blood flow to a part or parts of the brain is stopped
by a blockage in a vessel. Hemorrhagic stroke is more
deadly and occurs when a weakened vessel tears or ruptures,
diverting blood flow from its normal course and instead
leaking or spilling it into or around the brain itself.
of Ischemic Stroke showing blockage of one of the
brain's arteries.(right) CT scan of Hemorrhagic
Stroke. Arrow points to the area of blood in the
Treatment for each type is significantly different.
In fact, treating an ischemic stroke as though it were
hemorrhagic or vice versa could have life-threatening
consequences. Therefore, a reliable determination (diagnosis)
of which type has occurred is critical before treatment
There is a third type referred to as transient ischemic
attack (TIA) or “mini-stroke.” While they
are not true strokes because the symptoms are temporary,
TIAs are usually a warning sign of a stroke to come.
Heeding the warning signs of TIAs and treating the underlying
risk factors that trigger them can prevent many strokes.
A TIA is caused by a brief pause in blood flow to part
of the brain — the result of a temporary or partial
blockage. The symptoms of a TIA resemble those of a
stroke but they do not last as long. Most symptoms disappear
within an hour, although some may persist for up to
24 hours. Usually, no permanent brain damage occurs
as a result of a TIA. According to the National Stroke
Association, approximately 5 million Americans have
experienced at least one TIA.
Patients suffering a TIA may describe a “veil”
or “window shade” partly covering the vision
of one eye that clears up spontaneously after several
minutes. This represents the temporary blockage (occlusion)
of the retinal artery to the eye. There may also be
dizziness, imbalance, loss of coordination, confusion,
difficulty speaking or understanding, and generalized
There is no way to differentiate the temporary symptoms
of a TIA from those of an acute stroke. All patients
need medical evaluation urgently. About one-third of
those who have a TIA eventually will have an acute stroke.
Many strokes can be prevented by heeding TIA warning
signs and treating underlying risk factors.
The vast majority of strokes – approximately
83 percent — are ischemic. They are caused by
an obstruction of an artery leading to or in the brain,
preventing oxygenated blood from reaching parts of the
brain that the artery feeds. Ischemic strokes are either
thrombotic or embolic, depending on where the obstruction
or clot (thrombus or embolism), causing the blockage
Thrombotic stroke is caused by a thrombus (blood clot)
that develops in an artery supplying blood to the brain
— usually because of a repeated buildup of fatty
deposits, calcium and clotting factors, such as fibrinogen
and cholesterol, carried in the blood. The body perceives
the buildup as an injury to the vessel wall and responds
the way it would to a small wound — it forms blood
clots. The blood clots get caught on the plaque on the
vessel walls, eventually stopping blood flow.
There are two types of thrombotic stroke:
- Large vessel thrombosis,
the most common form of thrombotic stroke, occurs
in the brain’s larger arteries. The impact and
damage tends to be magnified because all the smaller
vessels that the artery feeds are deprived of blood.
In most cases, large vessel thrombosis is caused by
a combination of long-term plaque buildup (atherosclerosis)
followed by rapid blood clot formation. High cholesterol
is a common risk factor for this type of stroke.
- Small vessel disease
(lacunar infarction) occurs when blood flow is blocked
to a very small arterial vessel. It has been linked
to high blood pressure (hypertension) and is an indicator
of atherosclerotic disease.
Thrombotic disease accounts for about 60 percent of
acute ischemic strokes. Of those, approximately 70 percent
are large vessel thrombosis.
A blood clot that forms in one area of the body and
travels through the bloodstream to another where it
may lodge is called an embolus. In the case of embolic
stroke, the clot forms outside of the brain –
usually in the heart or large arteries of the upper
chest and neck – and is transported through the
bloodstream to the brain. There it eventually reaches
a blood vessel small enough to block its passage.
Emboli can be fat globules, air bubbles or, most commonly,
bits and pieces of atherosclerotic plaque, such as lipid
debris, that have detached from an artery wall. Many
emboli are caused by a cardiac condition called atrial
fibrillation—an abnormal, rapid heartbeat in which
the two small upper chambers of the heart (called the
atria) quiver instead of beating. Quivers cause the
blood to pool, forming clots that can travel to the
brain and cause a stroke. Cardiac sources of embolism
account for 80 percent of embolic ischemic strokes.
The signs of ischemic stroke are similar to those
of a TIA, except the damage can be permanent. The most
common indicator is sudden weakness of the face, arm
or leg, most often on one side of the body. Other warning
signs may include:
- sudden numbness of the face, arm, or leg, especially
on one side of the body;
- sudden confusion, trouble speaking or understanding
- sudden trouble seeing in one or both eyes;
- sudden trouble walking, dizziness, loss of balance
or coordination; and/or
- sudden severe headache with no known cause (most
common with hemorrhagic stroke).
The symptoms depend on the side of the brain that's
affected, the part of the brain, and how severely the
brain is injured. Stroke may be associated with a headache,
or may be completely painless. Therefore, each person
may have different warning signs.
Hemorrhagic stroke occurs when a vessel in the brain
suddenly ruptures and blood begins to leak directly
into brain tissue and/or into the clear cerebrospinal
fluid that surrounds the brain and fills its central
cavities (ventricles). The rupture can be caused by
the force of high blood pressure. It can also originate
from a weak spot in a blood vessel wall (a cerebral
aneurysm) or other blood vessel malformation in or around
Damage can be caused in two ways. As in the case of
ischemic stroke, oxygen- and nutrient-rich blood is
prevented from reaching the brain cells beyond the point
of rupture. In addition, leaked blood can irritate and
harm the brain cells in the areas where it accumulates.
It is the location of the hemorrhage, rather than the
amount of bleeding, that tends to be the bigger factor
in influencing the severity of the stroke. For example,
bleeds in the brainstem, though relatively tiny, can
be quite lethal, whereas the same-sized bleed in the
frontal lobe may not even be noticeable.
There are two types of hemorrhagic strokes. They are
differentiated by where the ruptured artery is located
and where the resulting blood leakage occurs.
called Intraparenchymal hemorrhage or intracranial hematoma)
This type of stroke is caused by the sudden rupture
of an artery or blood vessel within the brain. The blood
that leaks into the brain results in a sudden increase
in pressure that can damage the surrounding brain cells.
If the amount of blood increases rapidly, the sudden
and extreme buildup in pressure can lead to unconsciousness
Approximately 10 percent of all strokes are intracerebral
hemorrhages. They occur most commonly in the basal ganglia
where the vessels can be particularly delicate.
High blood pressure
(hypertension) is the most common cause of this type
of stroke. Less common causes include trauma, infections,
tumors, blood clotting deficiencies, and abnormalities
in cerebral blood vessels.
Blood Vessel Abnormalities:
Blood vessel abnormalities in the brain include arteriovenous
malformations (AVMs) and arteriovenous fistulas (AVFs).
AVMs and AVFs, also called lesions, are abnormal connections
between cerebral arteries (which carry blood to the
brain) and veins (which take blood away from the brain).
AVMs appear to be acquired prior to birth (congenital)
and tend to form near the back of the brain. Although
AVFs can be congenital, more often they are caused by
a trauma that damages an artery and a vein which are
side by side in the brain.
These blood vessel abnormalities can cause a host of
problems, but the two most common are pressure against
the adjacent parts of the brain, causing neurological
problems (such as seizures, paralysis or loss of speech),
and bleeding (hemorrhage) into surrounding tissues.
Hemorrhage from cerebral arteriovenous abnormalities
represents from 2 percent to 4 percent of all strokes.
Subarachnoid hemorrhage occurs when bleeding from
a damaged vessel causes blood to accumulate between
the brain and the skull, in the subarachnoid space,
and press on the surface of the brain instead of dispersing
into the tissue. The leaked blood can irritate, damage
or destroy surrounding brain cells.
When blood enters the subarachnoid space, it mixes
with the cerebrospinal fluid (CSF) that cushions the
brain and spinal cord. This can block CSF circulation,
which leads to fluid buildup and increased pressure
on the brain. The open spaces in the brain (ventricles)
may enlarge, resulting in a condition called hydrocephalus.
This can make a patient lethargic, confused or incontinent.
The large accumulation of blood increases the pressure
surrounding the brain, interfering with brain function.
The leaked blood also can produce a condition called
vasospasm in which the vessels narrow, impeding the
flow of blood to the brain. This can result in an ischemic
stroke. The condition typically develops five to eight
days after the initial hemorrhage.
Most often, a subarachnoid hemorrhage occurs because
a cerebral aneurysm, an abnormal bulging outward in
the wall of an artery, ruptures. SAH also can occur
because blood leaks from abnormal blood vessel connections
(AVMs and AVFs) near the surface of the brain.
A brain aneurysm is a weak bulging spot on the wall
of a brain artery very much like a thin balloon or weak
spot on an inner tube. Aneurysms form from wear and
tear on the arteries, and sometimes from injury, infection
or an inherited tendency.
There are two types of aneurysm:
– This is the most common type. It has a neck
and stem and is also known as a “berry”
aneurysm because of its shape.
|Illustration of a Saccular Aneurysm
– This is a less common type of aneurysm. It
is an outpouching of the wall on both sides of the
artery and does not have a stem.
|Illustration of a Fusiform Aneurysm
Aneurysms that cause subarachnoid hemorrhage are usually
located at the base of the brain in the Circle of Willis.
This is an area in which a lot of blood pressure changes
occur and where a lot of vessels branch off, which can
expose them to weakness.
Although it is not possible to predict whether an aneurysm
will rupture, an aneurysm is more likely to do so when
it has a diameter of 7 millimeters or more. Unruptured
brain aneurysms can be medically treated to prevent
a possible rupture.
Symptoms of a hemorrhagic stroke appear without warning.
The sudden increase in blood volume within the rigid
skull (cranium) creates intense intracranial pressure
that cannot be released. This, in turn, may trigger
a severe (“thunderclap”) headache, neck
pain, double vision, nausea or vomiting, loss of consciousness
or even death.
About 17 percent of strokes are hemorrhagic. The average
age at which people suffer hemorrhagic stroke tends
to be lower than for ischemic stroke. This is because
many of the risk factors are related to unhealthy behaviors,
such as smoking or drug use, rather than the effects
on the body of aging. The fatality rate for hemorrhagic
strokes is higher than for ischemic strokes and overall
prognosis is poorer.