Arteriovenous malformations (AVMs) are abnormal masses of blood vessels—arteries and veins called the nidus—that develop while an unborn baby is growing inside the mother’s uterus. The blood in the arteries dumps directly into the veins with no network of tiny capillaries in between, which normally occurs. And because the blood vessels that make up these masses are abnormally fragile, the malformations may bleed, leading to serious complications.
Although AVMs can occur anywhere (arms, hands, legs, feet, lungs, heart, liver and kidneys), about half of them are found in the brain, brainstem and spinal cord. Because they hemorrhage easily, AVMs can cause strokes, paralysis and the loss of speech, memory or vision. There is about a 10% fatality rate associated with an AVM hemorrhage. Visit Lurie Children's Division of Plastic and Reconstructive Surgery to learn more about AVMs that occur in parts of the body other than the brain.
Brain AVMs occur in approximately three of every 100,000 people, and about 40 to 80% of them experience some bleeding. It has been estimated that the annual risk of bleeding is about 1 to 4%. After age 55, the risk of bleeding decreases. Pregnancy and labor has been associated with an increased chance of AVM rupture. Although people are born with AVMs, the malformations are rarely discovered before age 20.
Some researchers suggest there is a genetic link for some AVMs, but no one is sure. The majority of AVMs are discovered in people ages 20 to 40. Some evidence indicates that the malformations develop when the unborn fetus is 45 to 60 days old, but other information suggests that AVMs are primitive structures left over after fetal blood-circulating systems develop.
Based on the clinical symptoms such as severe headache or neurological problems, the following tests may be used:
Typically, the first symptom of an AVM hemorrhage in the brain is either a sudden severe headache or seizures. The headache may be focused in one specific area or it may be more general. Sometimes the headache is mistaken for a migraine. Other symptoms may include vomiting, stiff neck, confusion, irritability, sleepiness, lethargy or weakness anywhere in the body.
Vision may also be affected; a person may experience decreased, double or blurred vision. About 25% of patients experience loss of vision, weakness or mental changes, depending on the exact location of the AVM.
Additional signs of a bleeding AVM in the brain are impaired speech or smell, dizziness, paralysis of the facial muscles, drooping eyelids, fainting, and ringing or buzzing in the ears.
The treatment team typically consist of a neurologist, neuroradiologist, neuropsychologist, neurosurgeon and anesthesiologist; a careful evaluation is key to successful treatment. The following are treatment options to be considered:
Approximately 10% of AVM hemorrhages are fatal. Seizures and neurological changes may be permanent in another 10 to 30% of cases of AVM rupture. If an AVM bleeds once, it is about 6% likely to bleed again in the next year if it is not treated. As time passes from the initial hemorrhage, the risk for further bleeding drops to about 3 to 4%, the baseline natural history risk. If the AVM has not bled, it is possible that it will bleed at a natural history risk rate of 3 to 4% per year. Some AVMs harbor features that make them more likely to bleed. Untreated AVMs can grow larger over time and rarely go away by themselves.
In children, surgical removal can cure the AVM, but long-term angiographic follow up is recommended since the AVM can recur in rare cases. In AVM’s that have been treated radiosurgically and have been documented as obliterated on 2-to-3-year post-treatment angiograms, long-term follow-up angiography is also recommended.