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An arteriovenous malformation (AVM) is a tangle of arteries that have developed abnormally. They may occur anywhere in the body.
Normally, blood flows from the heart into large arteries that lead to smaller arteries that lead to capillaries. The capillaries lead to small veins that lead into larger veins until the blood flows back to the heart.
When an AVM of the brain or spinal cord develops, medium sized arteries may feed directly into a vein. This puts an unusually large amount of blood through the vein. It also means that oxygen-rich blood doesn't get into the capillaries that normally feed the brain tissue.
Treating Arteriovenous Malformations at the Neurovascular Center
At the Neurovascular Surgery Center, we offer the full spectrum of treatment options for arteriovenous malformations and the aneurysms that sometimes come with them. In addition,the Neurovascular Surgery Center has state-of-the-art approaches for dealing with complications of AVMS such as stroke, blood clotting in the brain and neurological problems resulting from AVMS.
Complications of Arteriovenous Malformations (AVMs)
Overtime, as more blood flows through the AVM, the amount of blood going to the brain around the AVM may be reduced. This can cause seizures or neurological problems such as weakness or numbness in the limbs.
Sometimes, are associated with AVMS. (An aneurysm is a weak spot in the wall of an artery that bulges or balloons from the wall of the artery.) The aneurysm may be within the AVM or on an artery that feeds the AVM.
Either the aneurysm or the AVM may bleed. There is an estimated 3% to 4% per year risk that a cerebral AVM will bleed. If it does, there is an estimated 40% to 50% risk of a major stroke. Depending on where the bleeding occurs, a person could have weakness in the arms or legs, inability to speak or inability to understand speech. In severe cases, a person may go into a coma.
Unlike cerebral aneurysms, once an AVM has bled the chances of its bleeding again in the next several days do not go up. For this reason, surgery may not be needed when an AVM bleeds. The exceptions to this are if the bleeding is due to an aneurysm on an artery that feeds the aneurysm or if the bleeding is extensive. In the latter case, surgery may be needed to remove the blood clot.
Treatment Options for Arteriovenuous Malformations
There are four treatment options in dealing with AVMs:
- Conservative management
- Stereotactic radiosurgery
- Surgery to remove the AVM
This means managing a person's symptoms with anti-seizure medications. This may be recommended for very old patients with unruptured AVMs, or very large AVMs that present high risks if treated any other way. The decision to treat an AVM by conservative measures should be made in coordination with a neurovascular specialist.
Stereotactic radiosurgery delivers a single, high dose or radiation in a precisely focused way. This procedure causes the blood vessels to thicken and close off over a period of time, as long as 18 months to two years. Stereotactic radiosurgery may be advocated in certain AVMs which are small, typically less than 3 cm. Particularly if the AVM is in a deep location or if the patient is a poor candidate for surgery because of risks of anesthesia, etc.
Embolization is the injection of a glue-like material into the abnormal arteries to block them. During this procedure, the neurovascular surgeon uses an angiogram to help him or her place a small tube in the arteries feeding the AVM. When the tube has been properly placed, the glue-like material is injected into the arteries. This procedure is done to try to shrink an AVM before doing other treatments such as surgery or stereotactic radiosurgery. In rare cases, embolization may be used to eliminate a small AVM.
Surgical Removal of an AVM
Several factors are considered before an AVM is surgically removed. These include the size of the AVM, where it is located, how it is formed and its relationship to the arteries that feed the AVM and the veins that drain it. The patient's age and general physical condition are also taken into consideration in the decision-making process for surgical treatment.
Family Screening for AVMs
In most cases, AVMs of the brain and spinal cord develop spontaneously without a cause that can be identified. In these cases, there is no need for family screening. It is unlikely there is a genetic component. There are exceptions, however. The rare disease Osler-Weber-Rendu syndrome appears to run in families. It causes arteriovenous fistula in the lungs and related brain malformations. Usually there is a history of family members who have the condition.