Arteriovenous malformations, or AVM, are complex tangles of dilated, thin-walled blood vessel abnormalities. In the case of AVM, large arteries within the brain become directly connected to veins. Resultantly, the rapid, high pressure blood flow that normally occurs in the large arteries is delivered directly into the veins, bypassing the brain. This high pressure causes the thin, fragile blood vessels to expand and push against nearby areas of the brain or “steal” blood away from the surrounding brain tissue which can lead to a stroke or scarring of the brain. Moreover, the malformed arteries or the AVM itself may rupture, causing a type of stroke known as intracranial hemorrhage (bleeding within or around the brain). The blood that escapes from the ruptured AVM may damage the surrounding areas of the brain and/or cutoff or decrease normal blood flow to areas of the brain.
Arteriovenous fistulas or AVF are defined as abnormal connections (shunts) between arteries and veins, and are similar to AVM. AVF more often involve the arteries and veins and the coverings of the brain and spinal cord and cause symptoms either by increasing the pressure in the draining veins of the brain and spinal cord or by causing hemorrhage. Traditionally, the treatment for AVF was largely limited to open surgical procedures, which resulted in significant morbidity and mortality. Over the past 20 years or so, surgeons have perfected the treatment of AVF through minimally invasive endovascular embolization procedures using catheter technology, which is now the more common approach. The goal of treatment is to prevent hemorrhage or remedy the symptoms associated with increased pressure in the brain or on the spine.
When an AVM is diagnosed, an angiogram or arteriogram may be performed. This type of imaging study is used to view the blood vessel anatomy involved in the AVM, and to assist in developing a plan for treatment.
AVM Treatment Options
There are three major approaches to treating an AVM which can be used either alone or in combination. The type of treatment recommended will depend on the patient’s history and symptoms, as well as the features of the AVM including its size, location within the brain, and the arteries and veins involved.
Embolization is an endovascular technique that is used to block the vessels of the AVM. A tiny catheter or tube is inserted into the groin and guided via x-ray technology to the affected vessels in the brain that are causing the AVM. Material is then injected into the catheter to permanently block and close off the vessels. These materials might include glue-like substances or small platinum coils.
There is a large advantage to performing an embolization prior to undergoing other methods of treating AVM. Embolization can often decrease the size of the AVM, rendering radiosurgery or open surgery much safer. In addition, embolization may totally block the AVM’s blood flow, causing other types of treatment unnecessary.
Surgical treatment of AVM requires removing a portion of the skull so that microsurgical instruments can be used to remove the AVM. This procedure is often done in combination with embolization. Embolization prior to surgery is considered to be a lower-risk option than surgery alone.
Gamma Knife Radiosurgery
Despite its name, radiosurgery does not actually involve surgery. Instead, beams of radiation are used to cause scarring within the blood vessels of the AVM, thereby eliminating it. This procedure is recommended for patients with AVMs that are small and located in specific areas of the brain. Radiosurgery is generally successful in completely eliminating the AVM provided that the AVM is sufficiently small. However, a period of two to three years must pass before the full effect of radiosurgery can be determined. The obvious advantage of this procedure is that treatment can be provided without incision; however, it is not suitable for everyone.