The arteries carry the blood from the heart to the tissues and the veins carry the blood from the tissues to the heart.
It is an abnormal connection of the vessels in the tissues that surround the brain or spinal cord in which one or more arteries are directly connected to one or more veins or venous spaces called paranasal sinuses .
In an arteriovenous fistula or DAVF (for its acronym in English), there is a direct connection between one or more arteries and veins or paranasal sinuses that gives rise to many problems.
Arteriovenous fistulas differ from arteriovenous malformations in that the latter are located within the tissue of the brain or spinal cord, but the former are found in the lining of the brain or spinal cord, such as the dura mater or the arachnoid.
The most serious problem associated with arteriovenous fistulas is that they transfer arterial blood of high pressure to the veins or the venous sinuses that drain the blood of the brain or the spinal cord. This results in an increase in the pressure of the venous system around the brain or spinal cord.
Types of arteriovenous fistula
There are two main types of arteriovenous fistulas:
Dural arteriovenous fistulas and carotid-cavernous fistulas: These are acquired lesions, which means that patients are not born with them, but develop them later in life. They can be the result of infection or traumatic injuries, but most develop without any specific precipitating event.
Patients with dural arteriovenous fistula usually present with a thud in an ear that follows the heartbeat, which is called a murmur.
Patients with carotid-cavernous fistulas usually have swelling and redness of one or both eyes in addition to a murmur.
Although dural arteriovenous fistulas are found outside the brain, they can cause a wide range of neurological symptoms. The symptoms depend to a large extent on the drainage pattern.
Symptoms may include:
- Bruit (abnormal sound associated with turbulent blood flow).
- Tinnitus (ringing in the ears)
- Visual disability.
- Papilledema (swelling of the optic disk indicative of intracranial pressure).
How are dural arteriovenous fistulas diagnosed?
Currently, whenever possible, an attempt is made to close arteriovenous fistulas before the increase in pressure in the venous system causes irreversible damage to the brain or spinal cord.
The following tests can be used to diagnose a dural arteriovenous fistula:
- Magnetic resonance.
- Computed tomography.
Angiography, also called an arteriogram, is a special test in which a neuroradiologist injects a dye into the blood vessels of the brain and obtains images of the blood vessels. At this point, the angiogram is the test that most accurately shows the fistula and its relation to the surrounding arteries and veins.
Dural arteriovenous fistulas occur at an average age of 50 to 60 years, but people have been diagnosed at various ages. These abnormalities affect both men and women, but the hemorrhages of the DAVF occur more often in men.
These vascular abnormalities are usually acquired, which means that they are not present from birth. In most cases, the cause is not obvious. However, DAVFs may be associated with trauma, surgery, tumors or infection.
Arteriovenous fistula treatment
A combination of two methods can be used, depending on the type of arteriovenous fistula:
Minimally invasive endovascular embolization:
Typically enough to cure most arteriovenous fistulas.
During this procedure, a catheter is passed through the groin to the arteries of the brain that lead to the fistula and liquid embolic agents such as NBCA, glue or Onyx are injected into these arteries. This injection shuts off that artery and reduces the flow of blood through the arteriovenous fistulas.
Reserved for arteriovenous fistulas that can not be closed with endovascular embolization. During the microsurgical resection, a craniotomy is performed and, using the microscope, the fistula is isolated from the tissues surrounding the brain or spinal cord.