AVM stands for Arteriovenous Malformation is a tangle of blood vessels, that grew abnormally, and have a risk of bleeding. In almost all cases, it developed during the development of the child in utero. It basically involves two different kinds of blood vessels that should not be directly connected, actually being connected.

In the human body, there are 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 take 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 a potentially severe risk to the patient.

If the AVM occurs at a very young age and is a very high flow, it can cause other trouble, such as heart failure, etc.