Arteriovenous Malformations

WMK:

An Arteriovenous Malformation, or AVM, is an abnormal collection of blood vessels. Normally, oxygenated blood is pumped by arteries to the brain, where it enters a fine network of tiny capillaries. It is in these capillary beds where the blood nourishes the tissues. The deoxygenated blood then passes back to the heart through veins. Arteriovenous 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 most AVMs is not known. 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.

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.

AVMs can be seen on outpatient imaging studies such as CT's or MRI's. Angiograms are inpatient procedures needed to image the arteries and veins before any treatment. An angiogram is an x-ray movie of the blood flowing through the blood vessels. It is made by injecting contrast into the arteries going into the head and taking a series of x-rays films.

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. Each treatment has its advantages and disadvantages.

Embolization is a method of plugging the blood vessels of the AVM. Under X-ray guidance, 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.