Brain Arteriovenous Malformation (Brain AVM, BAVM)
Brain AVMs are an abnormal tangle of small vessels (called nidus) which directly connect brain arteries to brain veins, without any capillaries in-between (as should be normally the case). This results in a kind of short circuit, whereby blood goes directly from arteries, through the nidus, and into the veins, bypassing brain tissue, as seen in these images:
Why, when, and how AVMs form?
The short answer is that we don’t always know why or how. They are probably present at birth in tiny, microscopic forms at least in some cases. In a minority minority of patients, there is a genetic predisposition to forming the AVM (Wyburn-Mason syndrome, also known as CAMS, Hereditary Hemorrhagic Teleangiectasia, Clippel-Trenaunay-Weber syndrome, among others), but most cases seem to be “sporadic” or random. In the future, we will likely find abnormal genes in some of these people, but at the present time we don’t yet know what they are. The positive aspect of this is that in most AVMs are not inherited.
How do AVMs cause problems
First is bleeding — the vessels which make up the nidus are fragile and can rupture, which results in bleeding into the brain. Arteries which feed the AVM over time can form aneurysms (weakness in arterial wall which leads to bulging) which can rupture as well. These aneurysms behave very differently from the more common brain aneurysms, which are separately discussed. Finally, veins which empty or “drain” the AVM, over time can get either narrowed or enlarged, both of which can lead to rupture. The outcome of bleeding depends on location and extent of bleeding and subsequent treatment. Patients who survive bleeding may be left with permanent neurologic damage, such as paralysis. Some patients develop epilepsy (seizures) because of bleed-related brain damage. The overall probability or risk of bleeding at any given time is generally quite low — most AVMs have a bleeding risk of about 1-2% per year. This number adds up over a lifetime, and many patients with an AVM will bleed at some point, as in case of this patient, where arrows point to bright blood products inside the brain and brain ventricles:
Other ways in which AVMs cause problems is by “stealing” blood away from the brain. This can cause strokes (not bleeding types, but an ischemic ones) and seizures (epilepsy). In yet other patients, flow through the AVM competes with flow through the brain by congesting (backing up) veins, resulting in high venous pressures, which can cause seizures, brain dysfunction, and bleeding.
AVMs can form anywhere in the brain. Location of the AVM is one of the main determinants of what kind of neurologic problem will arise should the AVM start to “act up.” For example, AVMs in the left temporal lobe are likely to cause problems with making speech, because most people have their speech circuits in the left temporal lobe. AVMs in the brainstem (central part of the brain) cause all kinds of problems because of the many vital structures located there.
AVMs can be diagnosed either as a result of bleeding or other problems, or “incidentally.” With increased availability of MRI and CT scans, many patients are found to have an AMV after having a scan for an unrelated problem (such as CT scan after minor head trauma). Following AVM diagnosis, patients are usually referred to neurointerventional radiologist and/or neurosurgeon, and undergo a diagnostic cerebral angiogram.
Cerebral angiogram is a procedure where a small, long plastic catheter is put into large artery in the leg and under x-rays navigated into several neck arteries that supply blood to the brain. A contrast dye is injected through the catheter, and flow of dye from arteries through AVM and into veins, as well as contrast flow through normal brain vessels, is photographed by x-ray cameras. This provides specialists in AVM treatment with all manner of important information about the AVM that is necessary to decide how best to treat it. The vast majority of physicians specializing in AVM treatment require an angiogram before any treatment is contemplated.
Many additional diagnostic tests can be useful, such as MRI, MRA, CTA, EEG (for evaluation of possible seizure activity) and other tests. The exact sequence and nature of diagnostic tests depends on particular AVM characteristics and treating doctor preference.
Treatment issues and modalities are usually complex, and depend on a number of factors such as AVM location, size, bleeding history, perceived future bleeding risk, patient age and overall medical condition. Although excellent methods have been developed to assess AVM treatment safety, the approach remains highly individualized. Much does, and should, depend on your doctor’s preference. In general, three types of treatment are available — catheter embolization, surgery (by itself or combined with pre-surgical catheter embolization), and radiation.
1) Catheter Embolization – A catheter is introduced through the groin (like a regular cerebral angiogram) and navigated into an artery in the neck. Through this catheter, or series of catheters, a very small microcatheter is taken under x-ray into an artery which feeds the AVM, and this artery and parts of the AVM are embolized (plugged up) with a glue-like substances. Two main types are available — nBCA glue and Onyx. We usually perform this procedure under general anesthesia. This kind of treatment is attractive because it is not very invasive, there is no open surgery, and no scar. In this patient, whose CT scan with hemorrhage is seen above, the angiogram showed an arteriovenous malformation, outlined by the white oval. A microcatheter was used to deliver glue into the AVM, shutting it down completely. No surgery was necessary.
Only a minority of small AVMs can be completely cured by embolization. Most will still need to be surgically removed after embolization, though embolization can make surgery considerably smoother by reducing bleeding.
2) Surgery – only a minority of small AVMs can be completely cured by embolization. Most will still need to be surgically removed after embolization. Pre-surgical embolization can decrease blood flow through the AVM, allowing surgery to proceed in a more bloodless, controlled manner.In most cases, it is very important to remove the entire AVM to eliminate any risk of bleeding and other issues, which often requires surgery. Pre-surgical embolization can be done in one session or in steps, depending on factors such as size and anatomy. Finally, some AVMs are located in areas that allow for their removal by surgery alone, without the need for preoperative embolization. In this case, a left temporal lobe hematoma (arrows) is seen on an MRI study adjacent to an AVM nidus (inside white oval)
The angiogram shows an AVM, with an associated aneurysm – the site of bleeding. The arteries supplying the AVM are catheterized and glue delivered. After embolization, only a small part of the AVM remains. It is, however, important that the entire AVM be removed, and patient goes to surgery.
After surgery, the entire AVM is gone:
3) Radiation therapy — a relatively new method of treatment involves targeting the “nidus” of the AVM with a highly concentrated and potent form of radiation, often called “Gamma Knife.” Gamma knife can deliver very high doses of radiation to a precisely mapped area, while keeping radiation dose to everything outside of the target at relatively low levels. High doses of radiation to the nidus cause it to involute, or shrink, over time. Although this treatment has not been around as long as embolization or surgery, it is highly effective for the right kind of AVM. It is often the only reasonable treatment for AVMs located in vital parts of the brain, where embolization or surgery are not feasible because of high risks of brain damage. Gamma Knife is usually an outpatient treatment, and is non-invasive (although a cerebral angiogram is usually required for “targeting” the AVM). In centers with appropriate experience, overall results are excellent. Disadvantages include small but much feared possibility of radiation brain damage and lack of cure immediacy (irradiated AVMs are not cured right away, but slowly shrink over months to years). While the AVM remains “alive”, a risk of rupture remains.
This left temporal lobe AVM was treated by Gamma Knife in several sessions:
Follow up angiogram shows complete disappearance of the AVM:
Our Role: Brain AVM treatment should only be undertaken in a multidisciplinary fashion. Our role, as neurointerventional radiologists, is centered on performance of cerebral angiography and catheter AVM embolization, the NYU team consists of neurosurgeons, radiation specialists, diagnostic radiologists, neurologists, and other staff. To refer a patient or make an appointment, you can contact the Bernard and Irene Schwartz Interventional Neuroradiology Center at 212-263-6008