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AVMs: Knotty Problems

Brain arteriovenous malformations (AVM) are sometimes described as abnormal “tangles” of blood vessels in the brain. These tangles are notoriously tricky to treat. If they rupture (burst), the bleeding can be life-threatening, but surgery can also be risky. So experienced neurosurgeons must examine each case carefully to determine which option is likely to give the patient the best outcome.

At Columbia Neurosurgery, our department includes experts in these knotty situations. Neurosurgery Department Chairman Dr. Robert Solomon has treated more than 1,000 AVMs with microsurgery. Dr. Philip Meyers, Co-Director of the Neuroendovascular Service at NewYork-Presbyterian, has treated hundreds more using endovascular surgery.

On Wednesday, January 24, the two specialists will use Facebook Live to present on AVMs and answer questions from the public. The doctors will give an overview of AVMs, discuss when treatment is necessary and go over the latest treatment options. Viewers will be able to ask questions while the broadcast is live, or by commenting on the Facebook post in advance. It’s a great chance to learn from some of the leading experts in AVM treatment.

“Being an expert in AVM surgery is critical to achieving good results,” explains Dr. Solomon, and it is easy to understand why. Surgeons must evaluate the many treatment options—Gamma Knife, linear accelerator, embolization and microsurgery, for example—which can be used alone or in combination. Then the surgeon must perform the complex treatment or treatments. In general, surgeons who specialize in the problem are likely to have better overall outcomes when treating it.

Part of this expertise has to do with determining which patients are most likely to be helped by which treatments. To determine how risky AVM surgery is likely to be, surgeons evaluate three factors: an AVM’s size, location and blood flow. Each factor is worth a certain number of “points.” The total number of points is written as a Roman numeral between I and V, and that is considered the AVM’s grade.

The fewer the points and lower the grade, the less risky surgery is. As points increase, the risks of surgery increase, and other treatment options become more favorable. Note that only an expert should grade a specific AVM and direct its treatment—but in general, the system is as follows:


Size is worth up to three points. A small AVM (smaller than 3 cm) receives only one point. A slightly larger AVM, between 3 and 6 cm, receives two points. An AVM greater than 6 cm receives three points.


Location is worth up to one point. Neurosurgeons evaluate whether the AVM is located in a brain area that, if affected by surgery, would disrupt a specific function (e.g., movement, speech, vision, etc.). An AVM in such an area receives one point.


Blood flow is worth up to one point. If the AVM’s blood flow involves the brain’s deep venous system, the AVM receives one point. (There is some overlap with location here, as AVMs with deep venous drainage are also generally located more deeply in the brain.)

The neurosurgeon adds the total number of points to come up with the AVM’s grade:

Grade I

Very low risk to remove. The benefits of the surgery far outweigh the risks. An example of a Grade I AVM would be a small AVM located in a noncritical area right at the surface of the brain.

Grade II

Low risk to remove. This type of AVM may have received two points for being medium-sized, or one point for having a small size and one for its location or venous drainage. In any case, this AVM is also relatively low-risk for surgical treatment.

Grade III

Intermediate risk to remove. Grade III AVMs must be considered very carefully by experts. Some of these would be well-treated with surgery, and some with another method (see below). A medium-size AVM in an area critical to thought or speech would be an example of a Grade III AVM.

Grade IV and V

High risk to remove. The risks of surgery generally far outweigh the benefits for these AVMs. They are usually best treated with another method.

The other methods include endovascular embolization, or filling the AVM with a substance that blocks off its blood flow. This is a particular area of expertise for Dr. Meyers.

Doctors weigh the risks of the various treatments against the risk of not treating the AVM at all. “Unruptured AVMs have about a 3 percent risk of rupture per year,” explains Dr. Meyers.

Unfortunately, given the complexity of AVMs, it has been hard for doctors to get useful data about the risks and benefits of various treatments for particular types of AVMs. But Dr. Solomon and Dr. Meyers hope that is changing.

Dr. Solomon cautioned a few years ago that one big study, called ARUBA, didn’t get detailed enough to provide useful information. (We posted about his response to that study in The Lancet here.) But since then, more studies have been published that address some of ARUBA’s flaws.

“We hope that the available data becomes ever more useful for counseling and treating our patients,” says Dr. Meyers.

Dr. Solomon agrees. But while there remains more to learn about treating AVMs, he says, these knotty problems are best handled by experts in their care.

For more from the experts in AVM surgery tune in to on Wednesday 1/24 at 2pm EST.

Find out more about Dr. Robert Solomon on his bio page here.

Find out more about Dr. Philip Meyers on his bio page here.

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