June 13, 2020
Although rare, arteriovenous malformations (AVMs) in the brain can have devastating consequences. Brain AVMs account for about 2% of all hemorrhagic strokes each year and are often the cause of brain hemorrhage in children and young adults. AVMs vary greatly in terms of risks posed to patients, and there are several treatment options — further complicating care for patients with this intricate vascular pathology.
"Successful AVM management requires a deep dive into all these issues," says Bernard R. Bendok, M.D., chair of Neurosurgery at Mayo Clinic in Phoenix/Scottsdale, Arizona. "The treatment strategy must be matched to the particular AVM and the patient. There are multiple techniques for managing AVMs, and it's ideal to be seen at a center that excels in all of them."
Detailed anatomy of an arteriovenous malformation
Illustration shows the detailed anatomy of an arteriovenous malformation. Mayo Clinic is able to duplicate this complexity in 3D models to guide decision-making.
Determining the optimal treatment strategy requires detailed understanding of an AVM's anatomy. Mayo Clinic uses the latest imaging technology, including 3D modeling software and augmented reality visualization, to guide decision-making.
"When surgery is indicated, these imaging modalities help us to find a safe corridor and complete the surgery in an elegant fashion," says Chandan Krishna, M.D., a neurosurgeon at Mayo Clinic's campus in Arizona. "AVM is a pathology that requires not just one set of eyes, or clinicians working in silos, but a team approach."
Assessing an AVM's risks
The most potent factor influencing an AVM's risk to the patient is prior hemorrhage. But signs of AVM bleeding can be subtle. "Susceptibility-weighted imaging might be required to see the hemorrhage," Dr. Bendok says. "In addition, small hemorrhages that are thought to be caused by hypertension might actually be due to a micro-AVM."
Other important factors affecting an AVM's risk include size and location. In general, small AVMs and AVMs located deep in the brain are likelier to bleed. A brain aneurysm, which is found in about 20% of people with an AVM, also increases bleeding risk. "The aneurysm can pose greater danger to the patient than the AVM itself," Dr. Bendok says. "In that situation, if the AVM isn't treatable, treating the associated aneurysm might reduce the risk of bleeding."
Full understanding of an AVM's potential danger requires detailed imaging, starting with cerebral angiography. "Aneurysms and venous stenosis may not be seen on regular MRI," Dr. Bendok says. "Also, sometimes an AVM that is being monitored undergoes changes that can be detected only on advanced imaging. AVMs are three-dimensional — it's important to go beyond 2D views of a 3D problem."
3D view of aneurysm and intraoperative blood flow
On the left, augmented reality fluorescence technology provides a 3D view in color of an aneurysm (yellow arrow). On the right, fluorescence provides a 3D view of intraoperative blood flow.
To obtain clear views of cerebral anatomy and real-time blood flow, Mayo Clinic uses 3D models produced from MR angiography. "This technology quite accurately determines the amount of blood flow through the major blood vessels," Dr. Krishna says. Holography and augmented reality visualization provide additional information. "This combined imaging gives a better understanding of the flow dynamics to the AVM and the draining vessels, and how they intertwine with the underlying anatomy and functioning of the brain," Dr. Krishna says. "We can also see the normal vein tracks around the AVM, and then superimpose a functional MRI to plan a safe and effective surgical corridor. The more information we have, the safer the surgery becomes."
Matching treatment to patient needs
As a major tertiary center, Mayo Clinic offers the full range of treatment options for AVMs, including microsurgical resection, endovascular embolization and stereotactic radiosurgery. A new hybrid operating room allows patients to undergo angiogram and surgery in a single setting. Small AVMs can sometimes be treated with glue embolization to avoid surgery. Glue embolization can also be used to treat an aneurysm within an AVM. "Our 4D MRI is very helpful in showing us the impact of embolization on the AVM," Dr. Bendok says.
Radiosurgery can successfully treat AVMs that are less than 2 to 3 centimeters in diameter. Patients are closely monitored for recurrence of bleeding after radiosurgery, as it may take a few years for the AVM to resolve. Radiosurgery can also be used to treat AVMs considered inoperable, including AVMs located in the brainstem.
Arteriovenous malformation before and after staged radiosurgery
On the left, MR angiogram shows an arteriovenous malformation (yellow arrow). On the right, MR angiogram shows resolution of the malformation after staged radiosurgery.
For larger AVMs, Mayo Clinic uses staged radiosurgery: multiple radiation sessions, each aimed at a portion of the lesion. "Dividing the AVM into two or three pieces and treating each component three months apart has a 50% chance of obliterating the AVM," Dr. Bendok says. "Any remaining lesion becomes safer to remove surgically later." This use of combination treatments requires experience and expertise in multiple treatment strategies. "Mayo Clinic is able to integrate all of these modalities," Dr. Bendok says.
"Every AVM is unique — even AVMs with the same size and location are dramatically different from one another," Dr. Krishna says. "Careful study of the anatomy and all possible surgical solutions is critical for optimal management of this condition."