An Arterio-Venous Malformation, or AVM, is an abnormal collection of blood vessels. Normally, oxygenated blood is pumped by the heart through branching tubes called arteries to the brain, where it enters a fine network of tiny vessels called capillaries. It is in these capillary beds where the blood nourishes the tissues. The “used” (deoxygenated) blood then passes back to the heart through branching thin walled tubes called veins. Arterial-Venous Malformations are areas that lack the tiny capillaries. The location of the connection between the artery and the vein is called the shunt. The area of tissue is called a nidus of the AVM. An AVM can be thought of as a "Short Circuit" where the blood does not go to the tissues but is pumped through the shunt and back to the heart without ever giving nutrients to the tissues. What
causes AVMs? We don't know what causes most AVMs. People are born with AVMs although they do not appear to be hereditary. AVMs occur about equally in both sexes and in different races. An estimation of 3 million people in the United States are born with vascular malformation, 10% of which are AVMs. AVMs may be caused by a rupture or clotting of a blood vessel during fetal development. It is usually not associated with any other problems at birth.
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Most patients do not know that they have an AVM. A number of the patients with AVMs have seizures or persistent headaches. An AVM can put additional strain on the blood vessels and the surrounding tissues. For the very young (under the age of twenty) this is usually not a problem. The increased flow of blood caused by the shunt weakens the blood vessels. These weakened blood vessels can rupture. This is known as a hemorrhage or a bleed. If an AVM bleeds, the patient experiences an extremely severe headache. The bleed may cause a stroke and even death. About 4% of people with AVMs experience initial bleeds each year. The chance of bleeding is not known for those whose AVMs have bled previously. Larger AVMs occasionally may cause progressive neurological problems by putting pressure on the brain or by altering the blood flow.
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AVMs can be seen on outpatient
imaging studies such as CT's or MRI's.
A CT, or computerized axial tomography scan, uses x-rays to create
cross-sectional images of the body. An MRI or magnetic resonance
imaging scan uses magnetism and radio-waves to create a detailed
picture of the body. Patients will be put on a bed surrounded by
a tunnel-like magnet. Unlike x-rays, there are no known side effects
of MRI. |
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| What are the treatments
for AVMs?
Treatment options for AVMs include embolization, radiation, and surgery or a combination of these methods. Recent studies have revealed that for most cases, embolization is the safest and most effective procedure. To avoid bleeding, the aneurysm must be eliminated. Parietal treatment of the AVM is not known to offer any benefit except for very specific conditions. Each treatment has its advantages and disadvantages. Treatment decisions should be made with your doctor. |
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Embolization is a method of plugging the blood vessels of the AVM. Under X-ray guidance, a small tube called a catheter is guided from the femoral artery in the leg up into the area to be treated. Once the area is reached, glue or sometimes even a wire coil is placed to block off the area.
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| What happens during embolization?
During the embolization the
patient is awake but is made comfortable with the help of the anesthesia
team who monitors and gives him/her medicines by an intravenous line.
After the embolization, the patient usually spends the night in the
Neurological Intensive Care Unit (NICU) where he/she is monitored
closely. Patients are usually hospitalized for one night for each
embolization and usually require 2-3 embolizations at 2-6 week intervals.
Patients resume their normal full activity immediately upon each
discharge. There may be some mild headaches after the embolization
related to the blood vessels of the AVM clotting, or some nausea
related to some of the medicines that are given. What are "investigational studies"? • AVMs are a rare condition
affecting about 250,000 people in the United States. Much remains to
be known. These questions can only be answered by studies. All studies require the consent of the patient, approval of the hospital, and often the approval by the FDA and the company involved in making the medicine or material. You may be asked to participate in such study. The nature of the study and the reason for the study are explained in a consent form that you will be asked to sign. Many people with AVMs will never experience any adverse symptoms. With age, however, the risks of a rupture increase. The consequences of a rupture can be quite severe. In many cases preventative treatment is needed. Risks Many patients with AVMs have seizures or persistent headaches. If a rupture occurs, the patient almost always experiences an extreme headache. There is no known activity that is known to protect or cause a bleed. There is reservation, however, towards the use of aspirin, aspiring-containing compounds, or non-steroidal anti-inflammatory agents.
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