It's estimated that some 300,000 Americans are affected by arteriovenous malformations (AVMs). Simply put, an AVM is a tangle of dilated blood vessels in the brain. These vessels disrupt normal blood flow by pooling blood within the dense center, or "nidus," of the tangle.
The vast majority of people with AVMs will go undiagnosed and will suffer few if any symptoms from this congenital disorder. When an AVM is detected early, doctors monitor the blood vessels carefully because they can enlarge and cause problems over time.
In rare instances, AVMs can rupture. More commonly, patients between the ages of 10 and 30 may experience severe headaches or seizures or may suffer a stroke from a hemorrhage (bleeding) in the brain. More than 90 percent of patients who experience these problems survive with appropriate treatment.
Scans of a 9-year-old Gamma Knife patient with a 4.8 cc AVM.
Prior to treatment, patients undergo thorough, specialized imaging studies — usually computed tomography (CT), magnetic resonance imaging (MRI) and angiography — to determine the exact size, location and blood-flow patterns of the AVM. A multidisciplinary team then discusses the case to develop an appropriate treatment plan. Treatment usually involves some combination of embolization, open-skull surgery and Gamma Knife radiosurgery. It's important for the treatment team to have access to all of these options in a state-of-the-art facility housing dedicated angiography suites, microsurgical-equipped operating rooms and a Gamma Knife radiosurgery suite.
Embolization
Prior to radiosurgery treatment or open-skull surgery, patients with multiple AVMs or lesions larger than 3cm usually require embolization. The goal of this procedure is to diminish the amount of blood flowing into the AVM by filling it with specially designed particles, micro-coils or glue. The "emboli," or clots formed by these agents, plug the vessels of the AVM. This makes the AVM more manageable by decreasing the amount of bleeding that will occur during surgery, or by reducing the size of the nidus, which creates a smaller target for radiosurgery.
Open-skull surgery
If the patient has already suffered a bleed, surgery is often recommended to eliminate the immediate risk of another hemorrhage. Surgery is also usually indicated for AVMs that are larger than 3cm. In this case, embolization is usually performed prior to the surgery.
Using precise microsurgical tools, the neurosurgeon exposes the AVM and "resects," or removes, its nidus. If resecting all of the vessels feeding the AVM poses too great a threat of bleeding, the remaining AVM vessels may be treated effectively with radiosurgery after the open-skull surgery.
Gamma Knife radiosurgery
Gamma Knife radiosurgery, either alone or in combination with embolization techniques is often the best option for complex, deep-seated or brain-stem AVMs. Radiosurgery success is inversely related to the size and flow rate of AVMs — in other words, the smaller the AVM and the lower the bloodflow rate, the more successful radiosurgery is likely to be.
The effects of radiosurgery become clearer over time. In adults, AVMs of about 3cm generally take two to three years following radiosurgery to disappear completely. For reasons as yet unclear, radiosurgery benefits children with AVMs much more rapidly. It is not unusual to see a child's AVM disappear in less than one year and even six months past radiosurgery.
For small lesions (3cm or less), radiosurgery can eliminate nearly 80 percent of the AVM with less than 1 percent treatment mortality and less than 3 percent treatment morbidity. For larger AVMs (3-5cm), multiple treatments of Gamma Knife radiosurgery spaced one to three years apart may be an option until complete obliteration has been confirmed by angiography.
