Arteriovenous Malformations

Arteriovenous malformations (AVMs) are tangles of dilated, thin-walled blood vessels that occur anywhere within the brain or on the dura mater (the covering of the brain). If an AVM ruptures, it can cause a stroke, brain damage, or death.

AVMs are abnormal connections in which capillaries are absent, so blood is diverted directly from arteries to veins. There are several types of AVMs:

True AVM;
Occult or cryptic AVM or cavernous malformation;
Venous malformation;
Hemangioma; and
Dural fistula (includes three kinds).

An AVM can burst and spill blood into the brain, causing symptoms of hemorrhagic stroke.

WHAT ARE THE SYMPTOMS?

When they occur, common symptoms may include focal or generalized seizures or severe headache. Sudden signs and symptoms associated with hemorrhage into the braincan occur in minutes and may include:

Difficulty moving, speaking, or seeing;
Difficulty with memory;
Weakness or paralysis of a limb;
Dizziness;
Confusion; and
Hallucinations.

Rarely, patients present with slowly progressive neurological deficit caused by "steal" phenomena, wherein the high flow in the AVM steals blood from the brain, resulting in symptoms like the ones listed above but that slowly progress over months rather than rapidly developing as with hemorrhage. More than 50 percent of people who have symptoms experience intracranial hemorrhage.

CAUSES AND RISK FACTORS

Scientists don't know why AVMs occur; they appear to be congenital birth defects (present at birth, but are not hereditary) that appear more often in men than in women. There is a 25 percent chance of an AVM bleeding over the course of 15 years, and the risk of bleeding is slighter higher between ages 11 and 35. If a person has an AVM bleed, he or she is at slightly increased risk of recurrent bleeding for the next year. A second bleed increases the chances of more bleeds.

DIAGNOSIS

To diagnose an AVM, a physician may recommend one or more of the following:

Computed tomography (CT) brain scan;
Cranial magnetic resonance imaging (MRI) brain scan;
Cerebral angiogram or intra-arterial catheterization angiography;
Magnetic resonance angiography (MRA);
CT angiography (CTA);
Transcranial doppler (TCD);
Xenon CT scanning;
Carotid duplex scanning;
Radionuclide single-photon emission computed tomography (SPECT) scanning;
Transesophageal echocardiography; and
Electroencephalogram (EEG).

Before treating an AVM, physicians usually perform a Wada activation test on the patient.

TREATMENT APPROACH

The goal of treatment is to limit bleeding, control seizures, and remove the AVM(s) if possible. Treatment and the risks of surgery depend on the type, symptoms, location, and size of an AVM. If an AVM has bled, is in an area of the brain that is reasonable to treat, or is not too large, it will be considered for treatment. A bleeding AVM is an emergency that requires immediate treatment. A combination of the following treatments is likely:

Open surgery/surgical resection;
Microsurgery;
Stereotactic radiosurgery (Gamma Knife surgery);
Endovascular embolization/occlusion; and
Anticonvulsant medication.

If the AVM is in an area that is not easily treated, physicians may use conservative medical therapy. The patient may be instructed to avoid activities that may excessively elevate blood pressure, avoid taking anticoagulant drugs (such as warfarin), and have regular checkups with a neurologist.

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