So, it’s definitely nothing to do with cancer, though two of the available treatments are also used for tumours.
An AVM is an incorrect connection between your arteries and your veins. Your arteries are high pressure vessels that are used to pump blood away from the heart to every part of your body. As they get further and further away from the heart, they get smaller and smaller to make sure that the blood gets to everywhere at the same pressure.
Then, blood flows through a capillary bed and it is in these capillary beds that oxygen and nutrients are exchanged to the tissues of your body.
On the outflow side of the capillary bed is a vein and each vein flows together, forming bigger and bigger veins as the blood flows like a brook, then a stream, then a river back to the heart. Your veins are all low pressure vessels: no heart pumping them back, just the constant ooze of used blood from the capillaries.
An AVM is a tangle of blood vessels where one or more of the capillaries should be. The trouble with an AVM is that it doesn’t slow down the high pressure blood like a capillary bed does and it squirts into the vein at higher pressure than the vein is designed for. An AVM is an often complex set of vessels, letting through an amount of blood. Some people have a fistula, which I believe is like a shunt, a very direct connection from artery to vein in a big flow. I had a dural AV fistula.
Anyway, the risk with these things is that the vein isn’t designed for the high pressure arterial blood and over time can stretch and eventually split, leaking high flow blood into wherever your AVM is – if into your brain, it causes a haemorrhagic stroke, which is life-threatening or disability-threatening.
The other effects that an AVM can have are that the shortcut of blood round the circuit can lead to insufficient pressure in parts of your arteries, meaning the tissue being supplied with blood doesn’t get the oxygen or nutrients it needs and can die off (this is called necrosis). Secondly, the blood that is pumping into a vein doesn’t just flow “downhill” towards the heart because it is coming into the vein at high pressure, so it can flow a bit both ways along the vein. Where it flows back, against the normal return route towards the heart, it can again cause a disruption to the oxygenation and nutrient delivery to other nearby tissues and possible necrosis. (The reverse flow of blood in a vein is called “reflux” or “retrograde” flow).
Brain AVMs can also simply put pressure on nearby brain tissue which affects the working of the brain and lead to migraine-like headaches or seizures or other effects.
AVMs may need surgery or embolization or radiation therapy to close off the erroneous flow, or to clip it off or cut it out so as to remove the risk of a haemorrhage. Where an AVM is not in the brain or spine, other approaches/treatments are used.
… I’m no doctor and I don’t know if this is exactly how it all works but it is how I envisage it in my own case. Hope it helps.
Richard