Arteriovenous Malformations (AVM)
Arteriovenous malformations (AVM) involve an abnormal connection between one of the brain's arteries and veins. Although most AVMs are congenital, the exact cause of their formation is unknown. Approximately 0.14% of the U.S. population is affected with AVMs, and the incidence is equal in men and women.
AVMs are troublesome for many reasons. First, AVMs allow blood from the heart to bypass the brain's capillaries, which normally deliver oxygen and nutrients to the brain tissues. This may result in neurologic deficits.
The detoured blood also causes increased pressure on the fragile wall of AVM. The AVM may become swollen due to the effects of this pressure. The ballooned AVM can press down on adjacent brain tissue, inducing seizures or causing compressive damage to surrounding brain tissue.
A much more serious complication is the risk of an AVM hemorrhage (bleeding). This can be a life-threatening emergency, damaging surrounding brain tissues and in severe cases may even result in death. It has frequently been observed that small AVMs tend to bleed more frequently than larger ones. Once an AVM has bled, the re-bleed rate is 4% per year. Fortunately, hemorrhage from an AVM is rarely fatal (<10%), which is in contrast to the high mortality rate of ruptured aneurysms (>90%). However, neurologic deficits can still result from the compression and destruction of the surrounding brain tissue.
Symptoms
The presentation of AVMs varies from person to person. Unless the AVM enlarges or bleeds, it frequently causes no symptoms. AVMs may present with new onset seizures. Seizures resulting from AVMs often occur after age 20. The symptoms of AVM hemorrhage include sudden and severe headache, vomiting, vision change, abnormal weakness, decreased sensation or a change in mental status. The headache that often heralds hemorrhage from an AVM is similar to a classic migraine.
Complications and Treatments
Upon presentation, work-up includes a complete neurologic examination to detect any deficits. Additionally, CT or MRI scans of the brain are used to diagnose AVMs. Video X-rays of blood vessels using injected dye (angiography) can provide even more detailed images of abnormal vessels in the brain.
The final goal of the treatment is to remove or cut off the blood supply to the AVM. This will prevent further growth of the AVM and eliminate the risk of rupture. Current treatment options of AVM are surgery to clip off the AVM, embolization, radiosurgery or a combination of these therapies.
The location and size of the AVM, as well as the patient's overall health and desire to undergo surgery, must be considered in the ultimate decision as to which treatment is recommended. The technical challenges of surgically excising AVMs located in the critical or deep portion of the brain make it crucial that the surgeon performing the operation is highly skilled and well versed in the appropriate approach to the AVM. The neurosurgeons at the Maxine Dunitz Neurosurgical Institute have extensive experience in surgically excising AVMs.
Embolization of AVMs involves placing a long, thin flexible tube into a blood vessel in the leg. This tube is advanced through the blood vessel to reach the AVM, and a glue-like material is then injected into the abnormal vessel, cutting off the blood flow to the AVM. Occasionally, embolization is used in combination with surgery to allow for an easier and less hazardous operation.
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