Arteriovenous Malformations (AVM)
An arteriovenous malformation (AVM) in the brain is a complex tangle of thin-walled blood vessels—an abnormal connection between arteries and veins within the tissue of the brain or spinal cord—that can break more easily than normal, healthy vessels.
Unlike an aneurysm or stenosis, which can occur and be cured at any point in a person’s life, AVMs are usually congenital, or part of the brain from birth.
Symptoms of an arteriovenous malformation can vary depending on the location of the lesion and can include:
- Intracranial hemorrhage (more than 50% of patients)
- Seizures (20-25% of patients)
- Change in vision (double vision)
- Change in speech (garbled speech)
- Change in gait, strength, or coordination
WHAT CAUSES AN AVM TO BLEED?
An arteriovenous malformation contains abnormal, weakened blood vessels that direct blood flow away from normal brain tissue.
These abnormal blood vessels dilate, or get bigger, over time and can eventually rupture from the high pressure of blood flow from the arteries to the veins. The chance of having an intracranial hemorrhage (ICH) from an AVM is 1-3% per year.
WHAT HAPPENS IF AN AVM BLEEDS?
There is a 10-15% risk of death from the initial bleed and a 25-30% risk of permanent disability from the brain injury.
Most AVM’s are diagnosed after a patient shows symptoms, but sometimes are found incidentally. The most common testing approaches include:
- Computed tomography (CT) scan
- Magnetic resonance imaging and angiogram (MRI and MRA)—this looks at both brain tissue and the blood vessels of the brain
- Digital subtraction angiography (DSA)
Brain AVMs must be treated delicately and many patients are treated using a combination of therapies.
AVMs are a neurovascular disorder that require a neurosurgeon to have expertise in all three areas of treatment: conventional surgery, endovascular surgery and radiosurgery. In general, treatment of an AVM is recommended if it has bled, if it is an area of the brain that can be easily treated and is not too large in eloquent areas of the brain serving vital functions of the body.
A multidisciplinary team must consider the neuroimaging, anatomical, functional and dynamic information of an AVM patient before formulating a strategic treatment plan.
Creating the plan involves weighing the relative risks and benefits of a conservative approach vs. surgery vs. radiosurgery vs. embolization (deliberate blocking of a blood vessel or part of a blood vessel) or a combination of these therapies.
Treatment options include:
- Medical therapy
- Endovascular embolization
Of these options, the practice of embolization has advanced the treatment of AVMs most notably in recent years.
Embolization is a minimally invasive endovascular technique that consists of placing a microcatheter inside the AVM and injecting an embolic agent under x-ray guidance to occlude, or fill, the irregular blood vessels.
Craniotomy and AVM resection using microsurgery is a direct approach to remove the AVM and obtain cure. It is usually reserved for lesions located in more accessible areas of the brain.
Radiosurgery is another minimally invasive approach that involves aiming multiple narrow beams of highly focused radiation from different directions to converge directly at the AVM. The high dose of radiation concentrated only in the AVM and sparing the brain promotes a gradual occlusion of the AVM. This process will not cure the AVM immediately but rather over time the AVM “dies off.”
Our treatment of brain AVMs is greatly enhanced by incorporating a combined modality approach. For example, to make surgery significantly easier—and possibly reduce operating time and intraoperative blood loss—we might perform an embolization beforehand. Or, if we reduce the size of the AVM significantly either through surgery or embolization, the lesion may then be treated with stereotactic radiosurgery—and due to the resulting changes in the blood vessel walls, the AVM could be destroyed over the course of 2-3 years.
The key to successful treatment is to use the technology and the different options for treatment wisely for a positive patient outcome.
Videos courtesy of Rush University Medical Center.