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Brain Arteriovenous Malformations (AVM)
What is an AVM?
AVM stands for Arteriovenous Malformation. An AVM is a tangle of abnormal and
poorly formed blood vessels (arteries and veins). They have a higher rate of
bleeding than normal vessels. AVMs can occur anywhere in the body. Brain AVMs
are of special concern because of the damage they cause when they bleed. They
are very rare and occur in less than 1% of the general population. AVMs that
occur in the coverings of the brain are called dural avms.
Types of AVM
AVMs can occur anywhere in the body however BRAIN AVMs are of special concern
because of the damage they cause when they bleed. They are very rare and occur
in less than 1% of the general population. AVMs that occur in the coverings of
the brain are called DURAL AVMs.
What is the Cause of AVMs?
The cause is not known. AVMs are thought to be due to abnormal development of
blood vessels in utero and may be present since birth. Most AVMs are not
inherited with the exception of a condition called H.H.T. An AVM is not a
cancer, and does not spread to other parts of the body. Dural avms, in adults
are an acquired disorder that can occur following an injury.
Who Gets an AVM?
They can occur in people of all races and sexes in almost equal proportions. The
typical time of discovery is between the ages of 20 and 40 years.
Why is it Important to Treat an AVM?
Treatment is offered is to try to prevent bleeding from the AVM. Bleeding may
injure the surrounding brain resulting in a stroke , with possible permanent
disability or even death. The risk of bleeding is 4% per year, which means that
4 out of every 100 people with an AVM will have a bleed (hemorrhage) during any
one year. AVM's may also produce headaches, seizures and progressive paralysis,
and the treatment may alleviate these symptoms.
What are my risks of bleeding over my lifetime?
The risk of bleeding over one's lifetime may be high especially if the AVM is
discovered in a young person.
Table 1. Risk of Bleeding from an AVM
Life Expectancy Risk1 of Bleeding
10 years 33.5%
20 years 55.8%
30 years 70.6%
40 years 80.3%
50 years 86.8%
Example: Mr. J.L. is 40 years old and has an AVM. The risk of him bleeding over
the next 40 years2 is a little over 80%. This is Mr. J.L.ís cumulative risk of
bleeding over his lifetime.
1Cumulative risk of bleeding
2The average lifespan for a healthy Canadian male is about 75 years
What Kind of Symptoms do AVMs Cause?
Symptoms of an AVM:
A variety of symptoms may be produced which will depend on the location and size
of the AVM. Common problems including:
1. Seizures: An AVM in the brain may act as an irritant resulting in abnormal
electrical activity. Seizures may develop as a result of this hyperactivity.
2. Headache: Headaches may be caused by the high blood flow through the AVM .
These headaches may be similar to a migraine or be actual migraines. They may be
mild or quite disabling. Sudden, severe headaches can be caused by bleeding.
These headaches are often followed by nausea , vomiting , neurological problems
or a decreasing level of consciousness.
3. Stroke-like symptoms: Brain AVMs may cause stroke-like symptoms by depriving
the nearby brain tissue of oxygen and nutrients. The symptoms vary with the
location of the AVM and include:
Weakness or paralysis on one side of the body
Numbness and tingling
Problems with vision, hearing, balance, memory and personality changes
4. Bleeding: This is the most serious complication of an AVM. It is the main
reason for recommending treatment. Bleeding from an AVM will occur in about 4
out of 100 people with a brain AVM every year. Sometimes, a bleed may be small
and produce no noticeable symptoms. Approximately 50% of the bleeds are
significant with permanent disability in half of these cases and death in the
Note: It is important to know that an AVM can be present and not produce any
Why do AVMs Bleed?
AVMs are poorly formed blood vessels and because they are not built as strongly
as the normal blood vessels, they are more prone to bleeding.
Bleeding and Pregnancy
There is an increased risk of hemorrhage from an AVM during pregnancy usually
after the first three months of pregnancy. This hemorrhaging does not occur only
during labour. It is thought to be due to the increased blood circulation that
occurs during pregnancy. Although not all AVMs bleed during pregnancy, we
recommend delaying pregnancy until after the AVM has been completely treated.
How are AVMs Diagnosed?
There are three main tests that are used to diagnose AVMs. These are :
Cerebral Angiography (Angiogram): A thin tube is inserted into an artery in the
groin. This thin tube is threaded up to the blood vessels from the groin toward
the brain. Dye is injected into the blood vessels of the brain and pictures are
taken. An AVM will show up as a tangle of blood vessels. Doctors are able to see
the exact location and size of the AVM. This is the most accurate test.
Magnetic resonance imaging (MRI) : is a method of producing highly detailed
images of the body without the need for x-rays. MR angiography (MRA) utilizes
"pulse sequences " specifically designed to show the arteries and veins of the
brain as well as the AVM. MRI examination shows in detail the AVM and it
relationship to the brain.
Computerized Tomography (CT scan): uses X-rays to image different parts of the
body. CT scanning is an excellent method of detecting bleeding into the brain or
the fluid spaces around the brain. The study of the brain may be done either
without or with dye. On the CT scan it may be possible to see an arteriovenous
malformation of the brain, in particular after X-ray dye is given.
Your doctor will recommend the best treatment for you and this will be
determined by the size of your AVM and also the location. It is not uncommon to
recommend a combination of treatments.
Another option is to do nothing at all and just monitor the AVM. Your doctors
may recommend observation if they feel that treatment can not be offered safely
or when an AVM is discovered at a late age.
Under general anaesthesia a small catheter (plastic tube) is advanced from the
groin, into the brain vessels and then into the AVM. A liquid, non-reactive glue
is injected into the vessels which form the AVM to block the AVM off. There is a
small risk to this procedure and the chances of completely curing the AVM using
this technique depend on the size of the AVM. It is frequently combined with the
other treatments such as radiation or surgery.
This treatment is also known as Radiosurgery or Stereotactic Radiotherapy. A
narrow x-ray beam is focused on the AVM such that a high dose is concentrated on
the AVM with a much lower dose delivered to the rest of the brain. This
radiation causes the AVM to shrivel up and close off over a period of 2-3 years
in up to 80% of patients. The risk of complications is low. Until the AVM is
completely closed off, the risk of bleeding still persists.
This is the oldest method for treating AVMs. The AVM is surgically removed in an
operating room under general anesthesia. Since AVMs do not grow back, the cure
is immediate and permanent if the AVM is removed completely. The risks of
surgery are considered to be high for AVMs that are located in deep parts of the
brain with very important functions.