What is a dural arteriovenous fistula?
A dural arteriovenous fistula (DAVF) is an abnormal connection between the arteries and veins of the brain.
Normally a fine network of microscopic capillaries connects arteries and veins in all tissues including the brain. Capillaries assist in slowing down the blood flow between arteries and veins. A DAVF is a tangle of feeding arteries and draining veins in the brain that have abnormal connections which bypass the normal capillaries. The word “dura” refers to the membrane covering the brain and spinal cord. The high pressure blood flowing from arteries directly into thinner walled draining veins or venous sinuses results in a risk of brain haemorrhage (bleeding). This abnormal blood flow between arteries and veins is called a shunt. DAVF can vary in size, between a few millimetres to several centimetres and can occur anywhere in the dura directly outside of the brain or spinal cord.
The cause of DAVF in a specific patient may not be always be discovers. In general they are not thought to be inherited from parents but instead caused by previous blood clots in the large draining veins of the brain (called venous thrombosis), head injuries, previous brain surgery, or brain infections. Some types of DAVF, termed “high-grade” fistulas, have a risk of bleeding into or around the brain which may have severe consequences. The risk is further increased following a previous bleed. Other types of fistula may have very little risk, termed “low-grade”. Some patients have no symptoms and the DAVF is discovered incidentally on a CT or MRI scan. Nevertheless this does not mean that the DAVF carries no risk and further investigation is commonly required.