Cerebral
Aneurysm
A cerebral
aneurysm (also called an intracranial aneurysm
or brain aneurysm) is a bulging, weakened area
in the wall of an artery in the brain, resulting
in an abnormal widening or ballooning. Because
there is a weakened spot in the artery wall, there
is a risk for rupture (bursting) of the aneurysm.
A cerebral
aneurysm generally occurs in an artery located
in the front part of the brain which supplies
oxygen-rich blood to the brain tissue. A normal
artery wall is made up of three layers. The aneurysm
wall is thin and weak because of an abnormal loss
or absence of the muscular layer of the artery
wall, leaving only two layers.
The
most common type of cerebral aneurysm is called
a saccular, or berry, aneurysm, occurring in 90
percent of cerebral aneurysms. This type of aneurysm
looks like a "berry" with a narrow stem.
More than one aneurysm may be present at the same
time.
Two
other types of cerebral aneurysms are fusiform
and dissecting aneurysms. A fusiform aneurysm
bulges out on all sides (circumferentially). Fusiform
aneurysms are generally associated with atherosclerosis.
A dissecting
aneurysm may result from a tear in the inner layer
of the artery wall, causing blood to leak into
the layers. This may cause a ballooning out on
one side of the artery wall or it may block off
or obstruct blood flow through the artery. Dissecting
aneurysms may occur with traumatic injury. The
shape and location of the aneurysm may affect
what treatment is performed.
Most
cerebral aneurysms (90 percent) are present without
any symptoms and are small in size (less than
10 millimeters, or less than four-tenths of an
inch, in diameter). Smaller aneurysms may have
a lower risk of rupture.
Although
a cerebral aneurysm may be present without symptoms,
the most common initial symptom of a cerebral
saccular aneurysm is a subarachnoid hemorrhage
(SAH). SAH is bleeding into the subarachnoid space
(the space between the brain and the membranes
that cover the brain). A ruptured cerebral saccular
aneurysm is the most common cause (80 percent)
of SAH. SAH is a medical emergency and may be
the cause of a hemorrhagic (bleeding) stroke.
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 occurs. About 20 percent
of strokes are caused by hemorrhagic bleeding.
Increased
risk of rupture is associated with aneurysms that
are greater than 10 millimeters (less than four-tenths
of an inch) in diameter, a particular location
(circulation in the back portion of the brain),
and/or previous rupture of another aneurysm. A
significant risk of death is associated with the
rupture of a cerebral aneurysm.
Currently,
the cause of cerebral aneurysms is not clearly
understood. The formation of cerebral saccular
aneurysms has been associated with predominantly
two factors: an abnormal degenerative (breaking
down) change in the wall of an artery, and the
effects of pressure from the pulsations of blood
being pumped forward through the arteries in the
brain. Certain locations of an aneurysm may create
greater pressure on the aneurysm such as at a
bifurcation (where the artery divides).
The
forming of a cerebral aneurysm has also been linked
to risk factors that are inherited or may develop
later in life (acquired risk factors).
Inherited
risk factors associated with aneurysm formation
may include, but are not limited to, the following:
- alpha-glucosidase deficiency
- a complete or partial deficiency of the lysosomal
enzyme, alpha-glucosidase. This enzyme is necessary
to break down glycogen and to convert it into
glucose.
- alpha 1-antitrypsin
deficiency - a hereditary disease that may lead
to hepatitis and cirrhosis of the liver or emphysema
of the lungs
- arteriovenous malformation
(AVM) - an abnormal connection between an artery
and a vein
- coarctation of the
aorta - a narrowing of the aorta (the main artery
coming from the heart)
- Ehlers-Danlos syndrome
- a connective tissue disorder (less common)
- family history of aneurysms
- female gender
- fibromuscular dysplasia
- an arterial disease, cause unknown, that most
often affects the medium and large arteries
of young to middle-aged women
- hereditary hemorrhagic
telangiectasia - a genetic disorder of the blood
vessels in which there is a tendency to form
blood vessels that lack capillaries between
an artery and vein
- Klinefelter syndrome
- a genetic condition in men in which an extra
X sex chromosome is present
- Noonan's syndrome
- a genetic disorder that causes abnormal development
of many parts and systems of the body
- polycystic kidney disease
(PCKD) - a genetic disorder characterized by
the growth of numerous cysts filled with fluid
in the kidneys. PCKD is the most common medical
disease associated with saccular aneurysms.
- tuberous sclerosis
- a type of neurocutaneous syndrome that can
cause tumors to grow inside the brain, spinal
cord, organs, skin, and skeletal bones
Acquired
risk factors associated with aneurysm formation
may include, but are not limited to, the following:
- age (greater than 40
years of age)
- alcohol consumption
(especially binge drinking)
- atherosclerosis - a
build-up of plaque (made up of deposits of fatty
substances, cholesterol, cellular waste products,
calcium, and fibrin) in the inner lining of
an artery
- current cigarette smoking
- use of illicit drugs
such as cocaine or amphetamine
- hypertension (high
blood pressure)
- trauma (injury) to
the head
- infection
A risk
factor is anything that may increase a person's
chance of developing a disease. It may be an activity,
such as smoking, diet, family history, or many
other things. Different diseases have different
risk factors.
Although
these risk factors increase a person's risk,
they do not necessarily cause the disease. Some
people with one or more risk factors never develop
the disease, while others develop disease and
have no known risk factors. Knowing your risk
factors to any disease can help to guide you into
the appropriate actions, including changing behaviors
and being clinically monitored for the disease.
The
presence of a cerebral aneurysm may not be known
until the time of rupture. However, occasionally
there may be symptoms that occur prior to an actual
rupture due to a small amount of blood that may
leak, called "warning leaks," into the
brain.
The
symptoms of an unruptured cerebral aneurysm include,
but are not limited to, the following:
- headaches
- dizziness
- eye pain
- vision deficits (problems
with seeing)
The
first evidence of a cerebral aneurysm may be a
subarachnoid hemorrhage (SAH), due to rupture
of the aneurysm. Symptoms that may occur at the
time of SAH include, but are not limited to, the
following:
- initial sign - rapid
onset of "worst headache ever in my life"
- stiff neck
- nausea and vomiting
- changes in mental status,
such as drowsiness
- pain in specific areas,
such as the eyes
- dilated pupils
- loss of consciousness
- hypertension (high
blood pressure)
- motor deficits (loss
of balance or coordination)
- photophobia (sensitivity
to light)
- back or leg pain
- cranial nerve deficits
(problems with certain functions of the eyes,
nose, tongue, and/or ears that are controlled
by one or more of the 12 cranial nerves)
The
symptoms of a cerebral aneurysm may resemble other
problems or medical conditions. Always consult
your physician for a diagnosis.
A cerebral
aneurysm is often discovered after it has ruptured
or by chance during diagnostic examinations such
as computed tomography (CT scan), magnetic resonance
imaging (MRI), or angiography that are being done
for other conditions.
In addition
to a complete medical history and physical examination,
diagnostic procedures for a cerebral aneurysm
may include:
- digital subtraction
angiography (DSA) - provides an image of the
blood vessels in the brain to detect a problem
with blood flow. The procedure involves inserting
a catheter (a small, thin tube) into an artery
in the leg and passing it up to the blood vessels
in the brain. A contrast dye is injected through
the catheter and x-ray images are taken of the
blood vessels.
- computed tomography
scan (CT or CAT scan) - a diagnostic imaging
procedure that uses a combination of x-rays
and computer technology to produce cross-sectional
images (often called slices), both horizontally
and vertically, of the body. A CT scan shows
detailed images of any part of the body, including
the bones, muscles, fat, and organs. CT scans
are more detailed than general x-rays, and may
be used to detect abnormalities and help identify
the location or type of stroke.
- magnetic resonance
imaging (MRI) - a diagnostic procedure that
uses a combination of large magnets, radiofrequencies,
and a computer to produce detailed images of
organs and structures within the body. An MRI
uses magnetic fields to detect small changes
in brain tissue that help to locate and diagnose
a stroke.
- magnetic resonance
angiography (MRA) - a noninvasive diagnostic
procedure that uses a combination of magnetic
resonance technology (MRI) and intravenous (IV)
contrast dye to visualize blood vessels. Contrast
dye causes blood vessels to appear opaque on
the MRI image, allowing the physician to visualize
the blood vessels being evaluated.
Specific
treatment for a cerebral aneurysm will be determined
by your physician based on:
- your age, overall health,
and medical history
- extent of the condition
- your signs and symptoms
- your tolerance for
specific medications, procedures, or therapies
- expectations for the
course of the condition
- your opinion or preference
Depending
on your situation, the physician will make recommendations
for the intervention that is appropriate. Whichever
intervention is chosen, the main concern is to
decrease the risk of a subarachnoid hemorrhage,
either initially or from a repeated episode of
bleeding.
Many
factors are considered when making treatment decisions
for a cerebral aneurysm. The size and location
of the aneurysm, the presence or absence of symptoms,
the patient's age and medical condition, and
the presence or absence of other risk factors
for aneurysm rupture are considered. In some cases,
the aneurysm may not be treated but the patient
will be closely followed by a physician. In other
cases, surgical treatment may be indicated.
There
are two primary surgical treatments for a cerebral
aneurysm:
- open craniotomy (surgical
clipping)
This procedure involves the surgical removal
of part of the skull. The physician exposes
the aneurysm and places a metal clip across
the neck of the aneurysm to prevent blood flow
into the aneurysm sac. Once the clipping is
completed, the skull is sutured back together.
- endovascular coiling
or coil embolization
Endovascular coiling is a minimally invasive
technique, which means an incision in the skull
is not required to treat the cerebral aneurysm.
Rather, a catheter is advanced from a blood
vessel in the groin up into the blood vessels
in the brain. Fluoroscopy (a special type of
x-ray, similar to an x-ray "movie")
will be used to assist in advancing the catheter
to the head and into the aneurysm.
Once the catheter is in place, very tiny platinum
coils are advanced through the catheter into the
aneurysm. These tiny, soft, platinum coils, which
are visible on x-ray, conform to the shape of the
aneurysm. The coiled aneurysm becomes clotted off
(embolization), preventing rupture. This procedure
is performed either under general or local anesthesia.
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