Monday, July 28, 2008

Continuing AVM Education

Continuing AVM Education
Below is an explanation of what Arteriovenous Malformations are by Dr. Ed Zimney. This blog can be found on Dr. Z's Medical Report at

I appreciate very much Dr. Z's explanation of what AVM's are. He provides a very concise explanation. I have tried to post the weblink for the actual page in which he posted his explanation on AVMs (see however, the link would not work once I posted it with my favorite links. I have provided Dr. Z's main blog url though.

The Tangle of Arteriovenous Malformation as written by Dr. Ed Zimney 12/2006 at:

"An AVM is an abnormal tangle of blood vessels that develops before birth. They can be located anywhere in the body, but those in the brain or spinal cord are more likely to cause symptoms. It is believed that about 300,000 people in the U.S. have an AVM, while only about 36,000 (12 percent) have any symptoms and very few of these people have symptoms severe enough to be life-threatening. About 300 people (one percent) of those with AVMs die each year as a direct result of the condition.
Under normal circumstances, arteries, which carry oxygen rich blood away from the heart become progressively smaller and smaller until they become capillaries, the smallest blood vessels. Capillaries allow the oxygen from the arterial blood to enter tissues and cells where it is required for life. As the cells use up the oxygen, the deoxygenated blood begins to collect in the smallest veins. The veins grow in size until they eventually return all the blood to the heart and back to the lungs for reoxygenation. In an AVM, however, capillaries are bypassed and the small arteries are connected directly to the small veins. In addition, there are many of these abnormal connections giving an AVM the appearance of a tangled up knot of vessels. These tangled knots can vary in size from very small to very large.
Whether an AVM causes symptoms depends in part on its location and in part on whether the vessels leak blood or actually rupture. As noted above, arteries normally decrease in size gradually, which allows the blood pressure also to drop as the capillaries are approached. But in an AVM, the arteries connect right to the veins and expose the veins to a much higher blood pressure than normal. Veins are normally thin-walled because they do not need to withstand higher blood pressure and therefore they are not always able to handle the pressure. This can result in minor leaking of blood, without symptoms, all the way to a rupture with resulting hemorrhage.
If an AVM is small or located away from important structures, it may never cause symptoms unless it bleeds. But if an AVM is located close to important tissue it can press on the tissue and cause symptoms even without bleeding. Oftentimes, AVMs are located in the brain or spinal cord. The brain and spinal cord are tightly enclosed within bone and any abnormal growth can press on these tissues causing neurologic symptoms. Or they may just sit there, for example if they are flat and near the surface, and be unnoticed unless they begin to bleed. Bleeding inside the brain can cause major damage called a hemorrhagic stroke. This may require emergency surgery to remove the blood and to stop the bleeding.
If an AVM becomes symptomatic or if it bleeds, it may need to be treated. There are basically three approaches to treating an AVM and they depend on size, location and whether some of the vessels are actually supplying some tissue with oxygenated blood. One type of procedure is to insert a catheter through an artery and extend it to the AVM at which point some material is injected into the AVM with the hope of clogging it up so no more blood passes through it. This doesn’t always completely work and in some cases cannot be done because too much blood flow might be obstructed. Another approach is through surgery where an attempt is made to tie off parts of the AVM and to remove other parts of it. Because of the tangled nature of the AVM, this type of surgery can be very difficult or dangerous, especially if the AVM is in the brain.
The last technique is to use a highly focused radiation beam to damage the vessels in such a way that over time they simply shrink up and close off. This technique uses the gamma knife technology, which uses radiation as a surgical tool, with no actual cutting through the skin. Further developments in the field of treatment for AVMs will likely come from improved imaging techniques (e.g., MRI) combined with precisely delivered radiation."

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