The cause of AVMs is not known.
AVMs are presumed congenital (that is, present at birth). They are thought to arise from developmental derangements at the embryonic stage of vessel formation, at the fetal stage. However, this has never been clearly established and they may arise after birth.
Unlike the association of head trauma or other injuries with the development of dural arteriovenous fistulae (DAVF), there are no known environmental risk factors for AVMs.
Most AVMs are termed "sporadic", which implies that they arise spontaneously without a specific gene mutation being passed on from parent to child. There is no clear familial inheritance, except in families with Heriditary Hemorrhagic Telangiectasia (HHT). HHT patients are at some 10,000 fold higher risk of developing a brain AVM than the non-HHT population.
"HHT is a genetic disorder that causes abnormalities of blood vessels....A person with HHT has a tendency to form blood vessels that lack the capillaries between an artery and vein. This means that arterial blood under high pressure flows directly into a vein without first having to squeeze through the very small capillaries. This place where an artery is connected directly to a vein tends to be a fragile site that can rupture and result in bleeding. We usually call a blood vessel that is abnormal in this way a telangiectasia (tel-AN-jee-eck-TAZE-ee-ya), if it involves small blood vessels. We tend to call it an arteriovenous malformation (AVM) if it involves larger blood vessels. So, an AVM might be thought of as a big telangiectasia. The basic abnormality in the blood vessel is the same."
- Hereditary Hemorrhagic Telangiectasia Foundation (www.hht.org )