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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 other half.

 

Note: It is important to know that an AVM can be present and not produce any symptoms.



 

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.

 


 

Treatment


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.

Embolization

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.

Radiation Treatment

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.

Surgery

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.