Arteriovenous Malformation, or AVM, is an abnormal cluster of blood vessels in the brain or spine. While normal blood vessels carry blood with oxygen and other nutrients throughout the body, AVM vessels carry blood without nutrients. Most researchers believe that nearly all AVMs are congenital, or present from the time of birth.
Ordinarily, blood is carried from arteries that branch into capillaries throughout the body. Blood is then carried back to the heart through veins. With an AVM, however, arteries carry blood directly to veins, bypassing any capillaries and creating a short circuit of blood flow, referred to as a shunt.
What are the symptoms of AVM?
AVMs often don’t produce symptoms. In some cases, AVMs are discovered while other conditions are evaluated in what doctors call an incidental finding. If they are present, symptoms vary according to the location of the malformation. In rare cases, an AVM can cause epilepsy, neurological problems or pain. Cerebral AVMs can cause headache and epilepsy with other specific symptoms that usually depend on the location of the malformation and the individual.
What are the treatment options?
In rare cases, with seniors for example, it might be best to leave an AVM untreated and observe the patient over time. For nearly all other patients, there are three treatment options: surgical removal, endovascular therapy and stereotactic radiosurgery.
If an AVM is completely removed during surgery, the condition can be cured. However, brain surgery is invasive with risks that include stroke, infection, neurological problems and complications from anesthesia.
In a procedure known as endovascular therapy, doctors use an angiogram to image the AVM. A small catheter injects dye into the vessels, which are x-rayed. Doctors then use the catheter to inject special glue into the lesion. While the technique is less invasive than open surgery, it doesn’t always treat the entire AVM.
Partially treated AVMs are still capable of bleeding and causing a stroke. As a result, most neurosurgeons believe that a patient with a partially treated, or embolized, AVM remains at risk for future problems. Endovascular therapy is typically used to reduce the size of the AVM prior to surgical removal or stereotactic radiosurgery.
Stereotactic radiosurgery precisely aims radiation beams at the AVM from multiple angles. Over time, the radiation causes the AVM blood vessels to narrow and eventually close off, eliminating the risk of hemorrhage or stroke.
The primary advantage over surgical removal is that radiosurgery is noninvasive and doesn’t carry the risks of open surgery. Moreover, some AVMs are located in areas of the brain that cannot be approached safely with conventional surgery. In those cases, radiosurgery may be the only feasible treatment option.
Radiosurgery also can be used in conjunction with other AVM therapies. Doctors can use radiosurgery, for example, to eliminate an AVM remnant not removed during surgery. Radiosurgical treatment for AVMs is an outpatient procedure and allows patients to immediately resume normal routines.
Radiosurgery for AVMs carries a few disadvantages. First, the radiation can take up to three years to fully destroy the malformation, during which time patients remain at risk for additional AVM bleeding. It’s also possible patients can experience significant neurological damage as a result of an AVM hemorrhage after radiosurgery, even if the treatment is in the process of destroying the malformation.
Second, not all AVMs disappear after radiosurgery. Small AVMs, those with a diameter of 3 centimeters or less, have an 80 percent chance of disappearing after a single treatment. Larger AVMs have a lower rate. As a result, it’s not uncommon for only a portion of an AVM to disappear after radiosurgery. Such patients are often treated with a second course of stereotactic radiosurgery.
Finally, even if an AVM is cured with radiosurgery, symptoms can persist. Some patients who suffer headaches or seizures before AVM treatment, for example, continue to experience them even when the AVM is destroyed. In such cases, the cause is thought to be scar tissue that develops around the AVM during its formation as well as the process of destroying it.
CyberKnife differs from other radiosurgery systems in that it doesn’t require a rigid metal frame screwed to the patient’s skull for targeting tumors and immobilizing patients. The CyberKnife achieves highly accurate targeting with computer imaging that continuously updates the tumor location and, therefore, eliminates the need for a metal frame. Moreover, other radiosurgery systems are limited to treating AVMs of the brain. However, CyberKnife can treat AVMs in the spinal cord as well.