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Dural Arteriovenous Malformations (DAVM)

 

What is an AVM and a DAVM?


AVM stands for Arteriovenous Malformation. It is a tangle of abnormal blood vessels (arteries and veins).

A DURAL AVM is an arteriovenous malformation that occurs in the coverings of the brain - the dura - hence the name Dural AVM.



 

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.



 

Noises and AVMs


Noises or bruits are an inconsistent feature and are not specific to dural AVMs. Recent complaints of noises in the head of recent onset should be evaluated by a physician.



 

Stroke-Like Symptoms Due to AVMs


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.



 

Bleeding from Dural AVMs


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.



 

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:

  1. Neurological dysfunction
  2. An episode of bleeding
  3. Intolerable symptoms


 

Treatment


There are three options currently available for patients who are found to have a dural AVM:

  1. No treatment
  2. Embolization
  3. Surgery