What is a Brain Arteriovenous Malformation?
A brain arteriovenous malformation (AVM), also called a cerebral arteriovenous malformation or simply AVM, is an abnormal tangle of blood vessels in the brain. AVMs can cause bleeding in the brain, seizures, and other neurologic problems. They occur in less than 1% of the population. Most patients are born with their AVMs but in some cases AVMs can form later in life. The most common age for brain AVMs to be diagnosed is in the 30’s to 40’s, but they can be diagnosed in children as well as older adults. Men and women are equally likely to have an AVM.
Figure 1. MRI brain showing an AVM in the right occipital lobe.
How are AVMs discovered?
Unruptured AVMs often cause no symptoms and hence are discovered “accidentally” after brain imaging for other reasons. The most common first symptom caused by an AVM is bleeding in the brain. This occurs in 70% of symptomatic patients. Patients whose AVMs bleed often have sudden onset of a severe headache, and may also have weakness, nausea, vomiting, neck stiffness or sound/light sensitivity. In severe cases patients may progress to coma. Bleeding is associated with a 10-20% chance of death and a 10-20% chance of disability. Less commonly, the first symptom of an AVM is a seizure(25% of symptomatic cases). The average age of patients with seizure is 25 years. Less commonly, the first symptom of an AVM may be weakness or other focal neurologic symptoms that leads to the identification of their AVM. Headaches are common in patients with AVMs, with 5-15% of patients complaining of long-standing headaches before their AVM is detected. However, most people with chronic headaches do not have an AVM. The best available data suggests that AVMs have a 1-3% per year risk of bleeding once discovered.
How are Arteriovenous Malformations Diagnosed?
AVMs are diagnosed in different ways. Diagnosis of an AVM that has caused bleeding is typically made on Computerized Tomography (CT), which uses X-rays to view internal structures of your body, in this case, of your brain. In patients where the AVM has not caused bleeding, often Magnetic Resonance Imaging (MRI) is also performed, which uses magnetic and radio waves to create high resolution images of the brain tissue and surrounding structures.
To determine the exact location, size and anatomy of an AVM, the blood vessels in the brain are imaged in a test called “angiography.” Angiography can be performed non-invasively with CTA or MRA. Cerebral catheter angiography is the third option, which is an invasive test that requires a catheter to be placed into the arteries that supply the brain in order to inject contrast material (“x-ray dye”) for imaging of the blood vessels. Usually the catheter is placed into the leg artery in the groin and maneuvered into the brain arteries. The procedure involves minimal discomfort and may be performed with light sedation (the patient is awake) or general anaesthesia (the patient is asleep). Angiography is considered the “gold-standard” for imaging an AVM. It is an invasive test, with a very small risk of serious harm to the patient (most importantly a small risk of causing a stroke). It is performed in conjunction with CT or MRI as it provides additional information.
Figure 2. Cerebral angiography showing an abnormal tangle of blood vessels characteristic of an AVM.
How are AVMs Treated?
Today there are four management options for people who have been diagnosed with a brain AVM.
Medical therapy: medications are prescribed to manage symptoms if necessary (seizures for example). No effort is made to remove the AVM. This option may be chosen when attempts to treat the AVM with other means may pose more risk of harm to the patient than the AVM itself.
Surgical therapy: this requires opening the skull (craniotomy) in order to remove the AVM. In order for surgery to have any benefit, the entire AVM must be removed. Surgery immediately eliminates the risk of bleeding from the AVM but can also cause harm to the patient depending on the size of the AVM and where the AVM is located. For example, removing a larger AVM in a part of the brain that performs important functions is riskier than removing a smaller AVM in a part of the brain than is “less important.” After removing the AVM, the skull bone is secured in its original position.
Radiosurgery: whereby a single treatment of highly focused radiation dose is used to obliterate the AVM. Radiosurgery is performed by a team consisting of a neurosurgeon and radiation oncologist. Unlike traditional surgery, the effect of radiosurgery is not immediate; once administered the radiation destroys the AVM usually over a couple of years. While not always effective, radiosurgery has high cure rates for smaller AVMs, and is often the treatment of choice for AVMs in locations where traditional surgery would be very risky. There is a small risk of bleeding in the brain (usually delayed), and there is a very small chance of delayed development of malignant tumors.
Endovascular therapy: this is a minimally invasive procedure where catheters placed into the arteries, usually through the leg artery in the groin, are used to seal off the AVM with a glue-like substance (“embolization”). In some cases endovascular therapy alone can “cure” the AVM, but most AVMs cannot be cured this way. Most often endovascular therapy is used prior to radiosurgery or surgical removal of the AVM to make those treatments safer or more effective. The main risk of endovascular therapy is causing a stroke or bleeding in the brain.
Often multiple treatment options are combined, especially for difficult, large and complex AVMs. Selecting the appropriate treatment is critically important to give each patient the best possible prognosis. Patients are urged to seek treatment at centers that are experienced with AVM treatment and can provide all of the above treatment options.
Figure 3. Angiogram after surgical removal of the AVM.
Safety and Complications
Surgical risks and outcomes depend on AVM location, size and pattern of veins draining the AVM. The Spetzler-Martin grading scale, which combines these three factors, is used by surgeons to evaluate the surgical risks of resection of a given AVM.
The best method of treating an AVM should be determined on an individual basis. Immediately after a brain hemorrhage (bleed), the treatment may be to simply remove the blood clot and leave the AVM for treatment in a delayed fashion. In some patients after a large hemorrhage, the AVM and the blood clot may be removed at the same time. For unruptured AVMs, a detailed discussion of the risks and benefits of various treatment options including conservative management should be conducted with the patient and family.
There are inherent risks with either conservative or interventional treatment options. Data suggests a 1-3% per year risk of hemorrhage from an AVM. Given that most AVMs are identified in the 3rd or 4th decade of life, and the fact that AVM hemorrhage is associated with a 10-20% risk of death or serious disability, some patients may elect to undergo treatment for their AVM.
Which Procedure Should I Have?
The treatment of choice for an AVM, like all medical decisions, should be carefully discussed and decided upon by both the physician and the patient. In the case of both ruptured and unruptured AVMs, the treating physician should discuss the risks and benefits of each available treatment option. The physician will usually make recommendations for one treatment over another, depending on the facts of each individual patient.
A Note on “A Randomized Trial of Unruptured Brain Arteriovenous Malformations” or the ARUBA trial
The NIH-funded ARUBA was designed to guide the decision on whether to choose conservative or interventional treatment options for patients with unruptured AVMs. This particular clinical question was very challenging to uniformly study in a broad spectrum of AVMs with variable Spetzler-Martin grading risk features. Despite the results advocating a conservative approach to unruptured AVMs in the short-term, the management implications have been widely debated since the natural history of AVMs in the medically treated arm was not negligible (>3% rupture risk per year) and a longer term study follow-up is pending. Patients with unruptured AVMs would likely benefit most from discussing their management options with an experienced team of neurointerventionalists, neurologists, neurosurgeons, neuroradiologists, and radiation experts.