What is an AVM?

An arterial venous malformation is a nest of tangled blood vessels that may occur in many parts of the body. Normally, blood travels from the heart to all the body's tissues through the arteries. These arteries get progressively smaller to the point where they become very thin-walled capillaries. Nutrients in the blood enter and feed body tissues through the capillaries. The now nutrient-poor blood returns to the heart through the veins.

In AVMs, there are no capillaries and blood flow patterns are highly irregular (high pressure arteries feed into low pressure veins). When AVMS involve parts of the central nervous system (the brain, spinal cord and their respective coverings, specifically the dura), there is a danger of hemorrhage and stroke.

How do you get an AVM?

The most likely cause of AVMs is genetic. There are no known risk factors for the development of an AVM. Although about one quarter of all AVMs bleed or hemorrhage within the first 15 years of life, most AVMs are discovered between the age of 20 and 40. The majority of AVMs become symptomatic by age 50.

How often do AVMs occur?

Approximately one in 280,000 individuals, or just over one tenth of one percent of the population have AVMs.

How is an AVM detected?

Occasionally, an AVM may be detected in a routine medical exam by a physician who hears a bruit, that is, an abnormal sound heard when a stethoscope is placed over an artery. More commonly, individuals with AVMs may see their doctor because of severe headaches or seizures. Approximately 50% of all patients with AVM are first seen because of bleeding or hemorrhage. Most often, this is caused because of an "ictus", that is the sudden onset of severe headache which may be accompanied by a period of loss of consciousness. The symptoms of an ictus are caused by the AVM bleeding into the brain, into the fluid filled ventricles within the brain, or into the subarachnoid space (space surrounding the brain). Roughly 25% of all patients with AVM's are seen because of seizures. These are rarely life-threatening and may be controlled through the use of medications . Bleeds, however, are potentially debilitating and even life threatening. Because of this, all AVMs should be evaluated by a neurosurgeon.

How is it diagnosed?

A careful history and physical examination are the first steps in diagnosis. In most cases where bleeding in the brain is suspected, a CT scan will be obtained. This will almost always demonstrate the bleed. An AVM may have many "feeding" blood vessels. As much as 7 percent of AVMs will have an associated aneurysm. . If AVM is the suspected cause of a hemorrhage, a cerebral angiogram (an x-ray examination of your blood vessels) will most often be the next diagnostic test. Computer tomography (CT) scanning performed with and without contrast may also show an AVM. In the same manner, magnetic resonance imaging (MRI) and MRA will often show AVMs.

What are the treatment options and associated risks?

Treatment options depend upon whether or not there has been a hemorrhage, size, location, "feeding" arteries, draining veins, age and general health of the patient. In limited cases, AVMs may be inoperable, or the risks associated with operating may be too high. Therefore, observation may sometimes be the preferred course of treatment.

In general, there are three main treatment options. The first choice is usually open surgery which immediately cures the AVM. Surgery itself is the principle risk factor. Embolization, where a catheter is inserted to the point of the AVM and glue and other clotting materials are inserted into the AVM to stop unnecessary blood circulation, is sometimes as option. Embolization may be used to help surgery. Stereotactic radiosurgery is a third option, and is often used in the case of smaller AVMs. Because resolution of an AVM may take from one to three years following stereotactic radiosurgery, the principle risk from this non-invasive surgery is that the AVM will rupture prior to obliteration.

What risks are associated with AVM is left untreated?

The majority of AVMs present with symptoms by the age of 50. Approximately two to four percent bleed, or hemorrhage, annually. Left untreated, AVMs present a high risk of hemorrhagic stroke. Each bleed represents a 10% mortality risk and a 30-50% morbidity, or long-term health consequence.

Sacred Heart Neuroscience Center