General Information about Brain AVM
- An AVM is an abnormal collection of blood vessels where blood from arteries in the brain flows directly into draining veins without the normal capillaries in between. AVMs appear as a “tangle” of vessels.
- They are present at birth and appear in less than 0.14 percent of the U.S. population, or about 280,000 individuals.
- About one quarter of AVMs hemorrhage by age 15 and the majority become symptomatic by age 50.
- About half of patients with AVMs suffer a hemorrhage, or bleeding, and about 25 percent suffer seizures.
- Other symptoms include headaches, pressure on surrounding brain tissue, and bruits, or murmurs in a vessel caused by flowing blood that are audible to the patient.
- The cumulative risk of hemorrhage from an AVM is an estimated 2 percent to 4 percent per year. Each episode of bleeding carries a 30 percent risk of death and about a 25 percent risk of significant long term morbidity.
- AVMs can be identified by magnetic resonance imaging (MRI) brain scans. The scans also provide information about location and old hemorrhages without symptoms. AVMs also need to be evaluated by cerebral angiography to learn about the structure.
- AVMs are graded by the Spetzler-Martin grading system. This system uses three important characteristic of the AVM to arrive at the grade:
Size — the larger the size the higher the grade.
Location – eloquent areas of the brain (sensory, motor, language, visual cortex, hypothalamus and thalamus, internal capsule, brainstem) result in a higher grade.
Pattern of venous drainage—drainage from the veins into the deep structures of the brain result in a higher grade
- The higher the grade of an AVM the more difficult it is to treat, and the higher the risks associated with them.
Options vary according to the history and probable future of the AVM and patient age.
- Surgery is the most common approach.
Other treatment options include stereotactic radiosurgery, especially for small AVMs in critical locations. The risks of hemorrhage are not decreased until approximately two years after the treatment, but this approach avoids the risk of damage to critical structures and bleeding found in open surgery.
- Some AVMs may be treated by minimally invasive endovascular embolization to block blood flow through the vessels.