Dural Arteriovenous Malformation

Just what is this?

What is a DAVM?

DAVMs vary in size. Some are tiny and go unnoticed for many decades. Others form large and tortuous channels of arteries which pulsate strongly as they connect directly to their corresponding veins. AVMs can be found anywhere in the brain, including the brain cortex, the white matter, and the brainstem.

DAVMs are made up of arteries and veins which are connected in such a way that there is no capillary bed at all. This causes the pressure of the arteries to be transmitted directly into the veins within the AVM. This unusual flow of blood creates an area of high pressure and high turbulence that causes the AVM to become larger over time, and to affect the function of the surrounding brain tissue.

What Are the Causes of the Dural AVMs?

Unlike other brain AVMs which are congenital, dural AVMs are believed to be acquired. Dural AVMs are not infectious or inherited. A dural AVM is not a cancer, which means it cannot spread to other parts of the body. Occasionally, a dural AVM has been reported following cranial surgery.

Who Gets a Dural AVM?

Dural AVMs occur in people of all races and sexes. In a population of 1,000,000 people, less than 1 person will be found to have a dural AVM. 10-15% of all AVMs are dural in nature. There is a male-female ratio of 1:3 in dural AVMs. The reasons for the development of dural AVMs are unknown. They may result from a blood clot in a large venous channel which then forms a connection between a dural artery and vein during the repair. The risk of bleeding from a dural AVM is believed to be much less than from a brain AVM.

What are the Symptoms of a Dural AVM?

1. Noise in the head (bruit)
2. Pulsatile tinnitus (ringing in the ears)
3. Swelling or redness of eye (depending on location)
4. Stroke-like symptoms
5. Headache
6. Seizures
It is important to know that a dural AVM can be present and not produce any symptoms.

Stroke-Like Symptoms Due to DAVMs

Dural AVMs may cause stroke-like symptoms by overloading the veins in the adjacent brain tissue. The symptoms are unusual for a dural AVM and warrant treatment. The doctors call this "venous congestion" because the flow of blood through veins of the brain is slowed by the blood arriving in the veins of the brain coming from the dural AVM. The symptoms resulting from "venous congestion" vary with the location of the dural AVM and include:
-weakness of paralysis on one side of the body
-numbness and tingling
-problems with vision
-personality changes
-problems with balance
-problems with memory
-speech problems

Headaches and Dural AVMs

Headaches may be caused by the high blood flow through the AVM in the dura. As the dura has pain fibers, the patients may have the sensation of a headache. Your physician will try to determine if your headache is due to a dural AVM, but this may be difficult.

Bleeding from Dural AVMs

This is the most serious complication of a Dural AVM. It is one of the two reasons for recommending treatment. Bleeding from a brain AVM is believed to occur in 4 out of 100 people with a brain AVM every year. The risk of bleed from a dural AVM is not known but it is believed to be lower than 4% per year. The headache occurs suddenly and may be followed by nausea, vomiting, neurological problems or a decreasing level of consciousness. Sometimes, a bleed may be small and produce very mild symptoms.

Occasionally, if the veins are highly pressurized when they drain the blood from the arterial side of a dural AVM, the pressure may cause these veins in the brain to rupture. These veins have a thin wall that is meant to withstand low pressure normally found in the venous system. If the vein is constantly under high pressure - the vein "develops" into an artery.

Why are DAVMs so dangerous?

To understand why brain AVMs are dangerous it is important to first understand the way that normal blood vessels are connected with one another:

The Normal Artery-to-Vein Connection

There are two main types of blood vessels: the arteries and the veins. Arteries bring oxygen-rich blood from the heart and lungs into organs such as the muscles, bones and brain, and veins bring it back to the heart and lungs where it is re-oxygenated. As the arteries travel deeper and deeper into the tissues, they become thinner and thinner, until they reach a point of maximal narrowing - this area is known as the capillary bed. Blood flow slows down in order to be transferred from arteries into veins

Thus, one of the most important functions of the capillary bed is to relieve some of the pressure generated by blood as it flows through the larger arteries into the tissues.

Veins spring out of the capillary beds, and they get progressively larger as they exit the organs on their way to the heart and lungs, where blood is finally replenished with oxygen.

Abnormal Artery-to-Vein Connections

What Does a DAVM Look Like?

Diagnosis of Dural AVMs

There are three main tests that are used to diagnose Dural AVMs. These are:
Cerebral Angiography (Angiogram)
Computerized Tomography (CT scan)
Magnetic Resonance Imaging (MRI scan)

For the purpose of confirming the diagnosis of a dural AVM, everyone requires a cerebral angiogram. Dye is injected into the blood vessels through a plastic tube inserted into a vessel in the groin, and X-Ray pictures of the blood vessels in the covering lining (dura) of the brain. Sometimes, dural AVMs are discovered accidentally during CT or MRI scans for other unrelated problems. The CT scans and MRI scans produce images of slices through the brain. These tests help the doctors to see exactly where the dural AVM is located.

The following are indications for treatment of a Dural AVM:
Neurological dysfunction
An episode of bleeding
Intolerable symptoms

Treatments

1. No treatment
2. Embolization
3. Surgery
4. Gamma Knife

What is an Embolization Treatment?

In this form of treatment, a liquid, non-reactive glue is injected into the dural AVM to block off the feeding arteries. There is only a minute risk to this procedure. We know that the chance of completely curing the dural AVM using this technique is low, but it is an excellent method of reducing the symptoms such as noise or pain due to dural AVM.

Your doctor will recommend the best treatment for you and this will be, in part, determined by your symptoms, and by the size and location of your dural AVM. Many dural AVMs do not require treatment.

Surgical Treatment of Dural Arteriovenous Malformations (DAVM)

This is the principal method for treating dural AVMs that require treatment - specifically those dural AVMs that have bled or cause neurological dysfunction. The dural AVM is surgically removed in an operating room under general anaesthesia. Since dural AVMs do not grow back, the cure is immediate. An angiogram is done after the operation and the cure is permanent if the AVM is removed completely. The risks of surgery can be low for dural AVMs because it involves the lining of the brain only. For more information on the Gamma Knife proceedure please see the tab at the top of this page.

AVMs and Pregnancy

Intracerebral hemorrhage (ICH) and subarachnoid hemorrhage (SAH) of an AVM are uncommon complications of pregnancy. The occurrence of SAH during pregnancy is ~1:1,000 pregnancies, a rate that is five times higher then in non-pregnant women. In a review of all ICH complicating pregnancy, 77% were caused by aneurysms, and 23% by AVM. In compiling all of the data, it is noted that the AVM hemorrhages were in younger women, but there was no relation between hemorrhage and parity or gestational age. It is recommended that women with AVMs considering pregnancy consult with their physician. Many women go on to have normal pregnancies and deliveries

Your doctor will recommend the best treatment for you and this will be, in part, determined by your symptoms, and by the size and location of your dural AVM.