A dural arteriovenous fistula 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 found. 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. A DAVF in the brain has a risk of bleeding although some DAVF are more dangerous than others. If this does occur it may have severe consequences. The risk is further increased following a previous bleed.
You may have been referred for endovascular treatment if you have previously suffered a bleed as a result of a DAVF or have experienced common symptoms of DAVF such as tinnitus, decreased function of nerves supplying the head and face, problems with the eyes (bulging eye or visual disturbances), raised intracranial pressure, seizure, or other neurological symptoms. 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.
“Endovascular” means that access to the brain or surroundings is achieved by threading a very fine tube through your arteries. Embolisation is a way of blocking abnormal blood vessels and is usually carried out to prevent the DAVF from bleeding. This is done by injecting a special glue-like liquid into the DAVF to cut off the blood vessels supplying the fistula.
Endovascular treatment is performed by specialist doctors called interventional neuroradiologists (INRs)
If the DAVF is particularly large or complex, an embolisation may be performed prior to further surgical excision (removal) of the lesion to reduce blood flow to the DAVF and ensure that further surgical treatment is safer.
All treatments and procedures have risks associated with them. Risks may vary depending on the size, position, and configuration of the blood vessels. Rarely it is not possible to embolise a DAVF safely.
Minor, common side effects and risks
During the DAVF embolisation a contrast agent (iodine based) will be injected into the arteries. This allows for the doctor to visualise the blood vessels when an X-Ray is taken. Contrast agents are considered safe but have the potential to cause an allergic reaction. The department and team are well equipped to deal with reactions in the rare event of this happening. It is important that you contact the department as soon as possible before your procedure if you have reacted to an x-ray contrast agent before or have severe asthma and have been admitted to hospital with an asthma attack in the past year.
The contrast agent is excreted through the kidneys and may affect the kidney function after the procedure. This is more common in patients with pre-existing kidney dysfunction and some patients will have a blood test to test the kidney function beforehand to ensure that it is safe to have contrast.
The procedure will need to take place under a general anaesthetic. The anaesthetist will discuss the risks of general anaesthesia with you.
Serious but rare risks
DAVF embolisation may be a complex procedure. Serious complications are rare but possible:
The procedure may cause a stroke, the risk varies but is in the range of approximately 5% (1 in 20 patients) in most cases. This may be caused by rupture of the aneurysm during treatment or occlusion of blood vessels. Strokes can take different forms but most commonly involve weakness in the arms or legs and difficulty with speech or vision. This may be temporary or permanent, mild or severe.
There is a very rare risk of catastrophic brain injury resulting in death of approximately 1% (1 in 100 patients).
The use of X-rays during any procedure results in a very small increase in the risk of developing cancer in the future. Very rarely there is temporary hair loss and skin reddening that may occur up to a few weeks after the procedure.. We make every effort to reduce radiation dose to as low as possible.
We are required by law to ask patients of childbearing capacity between the ages of 12 and 55 years are required by law to be asked about the possibility of pregnancy when undergoing examinations involving x-ray. In the urgent case of a thrombectomy, the procedure will most likely still go ahead but with additional precautions in place. .
The small bruise at the place where the needle is inserted (usually the groin or wrist) may become large and uncomfortable and you may need more treatment, including surgery.
Surgical excision is an alternative. This involves making an incision in the skull (craniotomy) to allow the surgeon to access the DAVF. The feeding arteries and draining veins that remain in the brain are then clipped off. Surgery is a well established and effective treatment and can provide protection from DAVF rupture or haemorrhage. Surgical excision has its own specific risks and your neurosurgeon will discuss these in detail with you.
The DAVF embolisation is performed while you are under a general anaesthetic. The anaesthetic team will put you to sleep prior to the procedure. The procedure is performed by your doctor in the angiography suite in the neuroradiology department and it usually takes between one and three hours. A dedicated team of radiologists, radiographers, anaesthetists, and nurses in the angiography suite will monitor you closely throughout the procedure.
Once the procedure has started your doctor will place a thin flexible plastic tube (catheter) into the femoral artery in the groin or artery in the wrist. The catheter then passes through the main artery in the body called the aorta and finally into the arteries in the neck and brain (cerebral arteries). When the most accessible feeding blood vessel is identified, further catheters (including a microcatheter) are placed inside the first catheter and into this artery and up to the point of the fistulous connection. Embolic material (glue-like) is then injected into this point to obliterate the DAVF. Occasionally small platinum coils will be used in addition. The embolic material creates an artificial blood clot and blocks further blood flowing into the DAVF. X-Rays are taken during the procedure to ensure the DAVF is obliterated.
After the procedure the catheters are removed and the blood vessel in the groin or wrist is sealed off with a collagen plug or manual compression to prevent bleeding.
The procedure is done under a general anaesthetic and therefore you should not feel any pain. Sometimes it can be uncomfortable around the wrist or groin access site afterwards, but usually this settles with simple analgesics.
It usually takes 2-3 hours.
When you arrive on the ward you will need to stay in bed for a few hours to recover. During this time, the ward nurse will check you regularly, including looking at the site where you had the catheter put into your groin, to make sure there is no bleeding. If you do have bleeding, we will ask you to stay in bed resting a bit longer. You may have some bruising around your groin, which can be sore, but most people have little or no after effects.