Arteriovenous Malformations (AVM)
In an arteriovenous malformation (AVM), blood flows directly from arteries into veins. Ordinarily, capillaries connect arteries and veins to one another, but in an arteriovenous malformation, capillaries are absent. Columbia University Irving Medical Center/NewYork-Presbyterian Hospital is proud to be a regional center for excellence in the treatment of brain AVMs. Treatment may include one of several surgical options.
AVMs may occur within the brain itself or within the dura. Dural arteriovenous malformations and AVMs in the brain both have the potential to cause several complications:
- Hemorrhage: Typically, arteries accommodate high-pressure blood flow; blood flows through veins at lower pressure; and capillaries manage the intervening pressure gradient. Without capillaries, high-pressure blood surges from arteries directly into veins. Vein walls may weaken or rupture, causing hemorrhage and stroke—a medical emergency.
- Compression of affected area: Some AVMs can grow large enough that they encroach on nearby tissue or interfere with the flow of cerebrospinal fluid.
- Low blood supply to affected area: Without capillaries, the tissues around an AVM may not receive adequate nutrients from the blood, and cellular waste products may not be cleared as effectively.
AVMs vary widely in terms of size, location, type of blood flow, and many other factors. An AVM may cause all, some, or none of the complications listed above.
Some AVMs never cause noticeable symptoms. They may be found incidentally, during a brain scan performed for another reason.
When symptoms do appear, they tend to arise in midlife, in men slightly more often than in women. The presenting symptoms are likely to be serious problems like hemorrhage (approximately 50% of cases) or seizure (approximately 25% of cases).
A brain hemorrhage is a medical emergency that has the potential to cause disability or death; however, hemorrhage due to AVM tends to have a somewhat better prognosis than brain hemorrhage resulting from other conditions. This may be because of the younger age at which AVM hemorrhage tends to occur, or because the brain has already compensated to some extent for problems of blood flow and compression in the affected area.
Individuals with an AVM may also experience problems with speech, vision, or movement. Some patients with AVMs report experiencing headaches, especially with pain concentrated in the region of the AVM. With careful questioning, up to two-thirds of patients with an AVM report experiencing subtle learning difficulties as children.
An AVM is most often identified on CT (computed tomography) scans or MRI (magnetic resonance imaging) scans.
These are painless, noninvasive scans that use either X-rays (CT scans) or radio waves and magnets (MRI scans) in conjunction with a computer to form images of the body’s structures.
If an AVM is identified on CT or MRI, the next step is an angiogram. In this scan, a specialist injects a dye that can be seen on X-ray into the bloodstream, then takes X-ray images of the blood flow. Information gathered during the angiogram allows a neurosurgeon to plan the appropriate treatment for the AVM.
Most AVMs are formed during fetal development, at about eight weeks of gestation. The exact cause is currently unknown, and no risk factors have been identified. It seems that AVMs are not inherited.
AVMs are rare disorders, occurring in about one in 500 individuals.
Treatment decisions rely on weighing the risks of surgery against the risks of future hemorrhage or other complications. Experienced specialists consider the location and size of the AVM, whether it has hemorrhaged in the past, its pattern of blood flow, the pressure inside it and many other factors.
AVMs are assigned grades that reflect the level of risk inherent in their surgical removal.
- Grade I and II AVMs are low-risk for surgery. For young, healthy patients with Grade I or II AVMs, the best option is usually to have the AVM surgically removed.
- Grade III AVMs present a more complex treatment picture. Grade III AVMs are considered moderate-risk for surgical removal. Depending on features of the individual AVM, there may also be moderate or higher risk associated with not performing surgery. Grade III AVMs should be carefully evaluated by highly experienced specialists.
- Grade IV and V AVMs are considered high-risk for surgery. These are most often treated with medication and/or procedures like radiosurgery and embolization.
Surgical options include:
- Microsurgical resection: A neurosurgeon uses an operating microscope and specialized instruments to enter the skull, expose, and remove the AVM. Following this procedure, blood pressure must be strictly monitored and controlled, and a high-quality angiogram must be performed to confirm that the AVM has been completely removed.
- Embolization: A catheter is threaded from an artery in the groin through the circulatory system to the site of the AVM. There the catheter injects a “glue” or other substance that embolizes the malformed vessel. Embolization is often used to prepare for microsurgery or radiosurgery.
- Radiosurgery: During radiosurgery, an interventional neuroradiologist sends targeted doses of radiation precisely to the AVM. No incisions are made. The treatment is delivered in one session, and the vessels of the AVM shut down and shrink over the course of months or years. Gamma knife, proton beams, and linear accelerators can all deliver radiosurgery.
Studies consistently demonstrate that the best possible AVM patient outcomes are achieved by experienced surgeons and interventional radiologists at neuroscience centers of excellence, like Columbia Neurosurgery.