Arteriovenous Malformations (AVMs) | Boston Children’s Hospital

AVM stands for Arteriovenous Malformation. We believe that, in almost all cases, it developed during the development of the child in utero, and it basically involves two different kinds of blood vessels that should not be directly connected, actually being connected. In the body we have the arteries, which are the vessels that carry blood from the heart to the rest of the body. The arteries are thick walled and they’re designed to carry high flow and high pressure blood. Once the blood gets to wherever it’s going in the body, the arteries split again and again until ultimately they get to the capillaries which are the tiny microscopic vessels where the oxygen is given to all the tissues of the body. Once the oxygenation has taken place, it’s the veins that takes the blood back to the heart from the brain, and the veins are very thin walled and they’re designed to carry low pressure, slow flow blood back to the heart. So the arteries and the veins are quite different in how they’re built, and they really should not have blood in direct communication. An AVM consists of an area, where for some reason during development, the arteries and the veins are directly connected by a very tiny network of very small vessels, where there’s basically no pressure drop that’s happening, so you have the high pressure blood going straight from the arteries into the vein, as a kind of short circuit. That pressure builds up to the point where there’s a weak spot that eventually ruptures and causes a bleed. Thankfully, the initial bleed is often contained by the surrounding pressure within the skull. This allows a clot to form, which temporarily stops the flow of blood, stabilizing the patient. We still need to treat the AVM before that weak spot ruptures again, because every bleed in the brain is potentially a severe risk to the patient. If the AVM occurs at a very young age and is very high flow, it can cause other trouble, such as heart failure, for example, just because of the degree of flow through the AVM. Arteriovenous Malformations, as you heard Dr. Orbach say, is a tangle of blood vessels, that grew abnormally, and has a risk of bleeding, and so the goal of treating an AVM is to try to reduce that risk of bleeding, hopefully to make it go away altogether. There are basically four ways to treat an AVM. One way is surgery. You can just cut it out. And if you remove the AVM, the goal is by making it go away, hopefully you’ve taken away the risk of bleeding. A second way to treat an AVM is with radiation. It’s kind of like getting a sunburn. If you treat an AVM with radiation, over a period of time, those blood vessels begin to thicken up, and they begin to close off the tubing that blood travels through, and the end result is that the AVM shrivels up, and hopefully over a period of time, months, years, that AVM disappears. The third way to treat it is with embolization, and the idea there is something that Dr. Orbach can do, for example, where you can thread a very tiny wire up through the blood vessels inside the body, you can squirt different types of agents to plug up the pipes from the inside, which can help to slow down or stop the flow of blood inside an AVM. The fourth way to treat it is to observe it. Sometimes, the safest thing to do, if the AVM is very big or if it is in a very sensitive part of the brain, is to just watch it, because it may be that the risk of treating the AVM might have more side effects and might be more dangerous than leaving the AVM alone. The great thing about, I think, what we have here at the Cerebrovascular Center, is that we have all of those treatments available here, we can provide them individually or in combination, and when decisions are made to treat an AVM, they’re done with everybody at the table, and we try to put together the best plan possible for treating the child with their AVM.

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