Arteriovenous Malformations (AVM’S)
This information is intended to aid your understanding of brain arteriovenous malformations, (AVM's) and your treatment options.
WHAT IS A BRAIN AVM?
An AVM is a collection of blood vessels that are abnormal in the brain. The AVM is composed of a tangle of arteries and veins that form a clump. Arteries are the large, thick walled blood vessels that carry blood from the heart to the brain under high pressure; while veins are the softer blood vessels that carry blood back to the heart (veins can usually be seen on the back of your hand). The tangle of blood vessels that make an, AVM may be large, with the tangle web of blood vessels being several inches across, or small, perhaps the size of an olive. AVM’s are supplied by arteries that branch off of normal brain arteries. It can be visualized as a branch on a tree that goes to a bad portion of the tree. Typically there are one to four arteries that supply an AVM, occasionally more. These arteries can be blocked off or removed at surgery safely because they supply only the AVM, not the normal brain.
HOW DID I GET AN AVM?
We think most patients are born with their AVM, like a birthmark. There is no known cause for why people have AVM’s, and it is probably a random event as your brain develops. Drugs and trauma to the head are not thought to cause AVM’s. It is very rare that there is a family history of brain AVM’s, they are not inherited and other family members do not need to worry that they may have a brain AVM.
WILL MY AVM GROW LARGER?
Brain AVM’s do not grow like a tumor. Generally they remain about the same size after they are diagnosed. However the blood vessels that compose an AVM can change over time. Some arteries and veins may get larger or portions of the blood vessels may close up. Some blood vessels may dilate. These dilations on an artery are called aneurysms; on the veins the dilations are called “varices” (much like varicose veins that can occasionally be found on your leg). Rarely AVM’s may get notably bigger or smaller.
IS AN AVM THE SAME THING AS AN ANEURYSM, HEMANGIOMA, CAVERNOMA, VENOUS MALFORMATION OR ANGIOMA?
No, these are other lesions of blood vessels that can occur in the brain, but are very different from AVM’s.
WHAT CAN AVM’S DO THAT IS BAD?
There are basically three things that can happen to an AVM to cause problems: bleeding, seizures, or steal blood from the normal brain.
BLEEDING IN THE BRAIN FROM AVM’S
The blood vessels that make up an AVM are not normal; they tend to have weaker walls than normal blood vessels. Bleeding occurs when one of these blood vessels ruptures. If this occurs there is usually sudden onset of the worst headache of your life, different than a usual headache. Fortunately when an AVM bleeds it usually stops quickly, perhaps spilling a tablespoon of blood into the brain and then the hole in the vessels seals itself. If bleeding however continues, then it can make the patient much sicker, cause paralysis, blindness, difficulty communicating, thinking, or even threaten life. If an AVM bleeds there is a high risk that it will bleed again in the future, sometime over the next year. For this reason if an AVM has bled, we generally recommend it be treated to prevent rebleeding. This treatment may be delayed several days or weeks after the first bleeding episode because the risk of early rebleeding, within the first few weeks is quite low.
WHAT IS THE CHANCE MY AVM WILL BLEED IN THE FUTURE?
If the AVM has bled in the past there is a much higher chance it will bleed in the future. The overall risk that an AVM will bleed is thought to be 1% to 2% per year if there has not been a bleed in the past. Over a longer period of time, the overall risk is higher. When patients are followed for up to 25 years, about 25% of these patients will have a bleed or stroke from the AVM. The risk remains the same from year to year; it is just there is a longer time period over which the AVM can cause problems. To understand this risk, consider a car trip. The risk of having an accident is higher if you drive 100 miles than 10 miles. The risk of each 10-mile segment is the same, but you are exposing yourself to the risk for a longer time. However, if the angiogram shows risk factors for bleeding, such as aneurysms on arteries or abnormalities in the draining veins, then the risk is probably higher, and these finding are typical in AVM’s that present with bleeding. These risk factors are usually visible on the first angiogram that is done to evaluate the AVM. We will discuss these findings with you after your angiogram.
SEIZURES FROM AVM’s
Seizures, also called epilepsy, are a common finding with AVM’s. It appears the abnormal blood vessels irritate the surrounding brain and sometimes cause seizures. Usually medication such as Dilantin or Tegretol can control the seizures, even if the AVM is not treated, but some AVM’s, especially larger ones, cause seizures that cannot be controlled easily. Removal of an AVM does not always insure that seizures will be stopped. The AVM may cause some damage to the brain that results in persistent epilepsy, even after the AVM is cured. Generally however, successful treatment of an AVM provides better control of seizures.
OTHER EFFECTS OF AVM’S
An AVM is fed by arteries that carry blood to the brain, and after the blood passes through the AVM it returns to the heart through veins. Some of these same arteries also carry blood to the normal brain. Sometimes the AVM can in a sense steal blood from the normal brain, by diverting the blood to the AVM. If this occurs a patient may notice weakness in the arm, hand or leg, difficulty speaking, and occasionally difficulty thinking clearly.
HEADACHES AND AVM’s
Many patients complain of headaches and the cause is not always clear especially if the AVM has never bled. Patients with large AVM’s and AVM close to the surface of the brain seem to have more headaches. After removal of an AVM patients generally find their headaches better.
HOW IS AN AVM DIAGNOSED?
The presence of an AVM can usually be diagnosed on an MRI scan or CT scan. However, to define the risk factors for an AVM and plan treatment it is necessary to do a conventional cerebral arteriogram. A MRI type of angiogram does not aid in planning treatment. We have prepared a similar paper that describes angiography and you should review that brochure.
WHAT DOES THE ANGIOGRAM SHOW IN AN AVM?
An angiogram is performed for several reasons. It confirms the diagnosis of the lesion, allows planning for treatment, and informs us about whether you have a high or low risk lesion. While an MRI or CT scan usually can diagnose an AVM, the angiogram is used to confirm that diagnosis. Sometimes the angiogram shows you have some lesion other than an AVM, such as a hemangioma, cavernoma, or venous malformation. Occasionally an angiogram will demonstrate other vascular abnormalities associated with AVM’s including aneurysms. Brain AVMs can be either moderate risk or high risk. The angiogram shows abnormalities on blood vessels that lead us to think the AVM has a high risk of bleeding. These findings include aneurysms on arteries or dilations in the veins, both of which appear to be related to increased risk of bleeding. If these two findings are not present, there is still a risk the AVM can bleed, but perhaps the risk is lower.
HOW ARE AVM’s TREATED?
There is basically three treatments for brain AVM’s:
1. surgery to remove it,
2. stereotactic radiation (SRS) to lead to scar formation in the blood vessels and close the AVM, and
3. embolization to plug up the blood vessels that compose the AVM.
SURGERY FOR BRAIN AVM’s
Surgery has the advantage of leading to immediate cure of the AVM, as the purpose of the surgery is to cut out the AVM from the brain. Your surgeon who would do the surgery will talk with you in details about this type of therapy, including the risks, benefits and alternatives. Embolization can make surgery safer and easier by blocking off the arterial supply to the AVM. This procedure allows the surgeon to cut out the AVM with less risk of bleeding during surgery.
STEREOTACTIC RADIOSURGERY FOR BRAIN AVM’s
Also known as “SRS”, and uses either a linear accelerator or gamma knife, both about equal in terms of safety and effectiveness, this procedure can lead to scarring of the abnormal blood vessels that make up an AVM, leading to cure of the AVM. The advantage to this approach is that it avoids surgery, although it may take years to become effective and retreatment may be necessary. Your radiation therapist who delivers this therapy will talk with you regarding the procedure, risks, benefits, and alternatives. Embolization may make SRS more effective by reducing the size and flow through the AVM.
WHAT IS EMBOLIZATION FOR AVM’s
Embolization is a procedure that is commonly done as part of the therapy for brain AVM’s. This procedure may be done prior to surgery or SRS, or sometimes as the sole therapy for an AVM. The procedure involves doing an angiogram, even if one has been done in the past. If you do not understand what an angiogram is please refer to the other pamphlet, which describes that procedure in detail, and make sure your questions are answered about that procedure. At OHSU we have the most advanced imaging system in the region for performing these procedures, including a Philips biplane unit, which allows simultaneous x-rays to be taken from the front and the side of the patients head. This capability allows us to see the catheters in your head from both the front and side at the same time. Once a catheter has been put in the artery in the leg and navigated into the artery in the neck (carotid or vertebral) leading to the brain, pictures are taken and saved. These pictures of the arteries in the neck and brain provide a roadmap to the AVM. The pictures are stored in a computer and displayed continuously on the monitor. We then take a much smaller catheter, called a “microcatheter”, and navigate it over a very thin wire, called a “microguidewire” into the arteries of the brain leading to the AVM. Typically there are from one to four arteries that lead to an AVM, occasionally more. The microcatheter is then navigated over the wire to the AVM. To do this we are constantly using the x-ray and roadmap to go into the desired blood vessels. At any point of a branching of blood vessels, we can steer the microcatheter right or left, up or down, to select the blood vessel we want to enter. As noted above, the artery that supplies an AVM goes directly into the AVM, and does not go to normal brain. Once the microcatheter is in place in the artery, that artery is blocked off.
HOW ARE THE ARTERIES TO AN AVM PLUGGED UP DURING AN EMBOLIZATION PROCEDURE?
Arteries in the brain that supply an AVM, as well as all arteries, are like water pipes in your house, and can be plugged up with a number of different devices. We generally use particles that look like sand, or tiny platinum wire coils that look like steel wool, or glues. Each of these have certain risks and benefits, and we make the decision about which agent to use based on our experience of what will be safest for the patient and most effective for a particular patients AVM. Often a combination of agents is used. These embolic devices have been used for years and have no known long-term adverse effects. They may or may not be removed if surgery is done, but do not cause problems if left in place. The embolic agents are either pushed or injected gently through the microcatheter and out the tip into the artery supplying the AVM. Once the artery is plugged up the microcatheter is removed from the artery and directed into other abnormal arteries supplying the AVM.
DOES AN EMBOLIZATION PROCEDURE HURT?
The plugging up of an artery is painless. However, movement of the microcatheter in the brain can cause headache pain during the course of the embolization procedure. We generally place you under a general anesthetic and have you completely asleep for these procedures so you will not be uncomfortable. After an embolization procedure occasionally patients will complain of a headache, it should not be severe, and we will give you pain medicines as necessary.
HOW LONG DOES AN ANGIOGRAM AND EMBOLIZATION PROCEDURE TAKE?
The length of time to take pictures (the angiogram part) and do the embolization may last from about one to three hours.
WHERE SHOULD MY FAMILY AND FRIENDS WAIT?
If your family or friends accompany you, they can come to the IRU with you and wait. During the procedure there is a waiting area by the 11th floor elevators (Family Waiting Room) and progress reports will be sent out to the family members or friends if you so wish. We will discuss the results of this test with your family if you want us to do so. We can only send progress reports to your family if they are in the 11th floor Family Waiting Room. If the phone rings they should answer it, as we will call out at the beginning of the procedure and every hour until the procedure is finished.
WHAT ARE THE RISKS OF THE EMBOLIZATION?
The risk that something will go wrong during an embolization procedure is low. We make every effort to insure the procedure will go well. There are however risks whenever catheters are put in the body and brain. The risks include blocking a normal artery in the brain and causing a stroke, or having an artery bleed during the course of the procedure. Strokes and bleeding in the brain can be life threatening, or result in paralysis, blindness, difficulty communicating, or other bad things. These normal blood vessels could be inadvertently by the embolic device moving into the wrong artery, blood clots forming on the catheter, or damage from the catheter as it is moved through the arteries. Rarely catheters get stuck in the artery and cannot be removed. This rare complication generally does not cause any problems. We do many things to try to prevent these problems from arising. Another risk is that we are attempting to block off bad blood vessels in your AVM, and in trying to do so we may find that the risk are higher than we expected. In this case we would stop the procedure without accomplishing our original goals. Some embolization procedures can be lengthy, and the x-rays can cause temporary hair loss. If you experience this hair loss, be assured that it will grow back. The typical places for this hair loss are on the back of the head or above the right ear.
WITH THESE RISKS BEING WHAT THEY ARE, WHY SHOULD I UNDERGO AN EMBOLIZATION PROCEDURE?
The presence of an AVM by itself presents risks to the patient of bleeding, strokes, and seizures, as described above. We feel these risks exceed the risk of our treatment of the patients AVM. At OHSU we have performed over 2,500 embolization procedures of lesions in the brain, head and neck, and spine, including AVM’s. This extensive experience is one of the most important factors determining the safety of this procedure. As a general guideline we think that if the risk of an embolization were less than 5%, meaning a 95% chance of a good outcome without significant problems, then we would perform the procedure. Most AVM’s treatments are straightforward and the risk in the majority of cases is much less. Every AVM is different, and with our past experience will discuss with you in more detail any particular risk factors associated with planned treatment of your AVM.
COULD I NEED MORE THAN ONE EMBOLIZATION PROCEDURE?
Most AVM’s can be treated in a single session. Occasionally if the AVM is large or difficult to gain access, additional procedures may be necessary.
AFTER THE EMBOLIZATION, WHEN WOULD I HAVE SURGERY OR STEREOTACTIC RADIOSURGERY?
The embolization procedure generally results in permanent blockage of the artery. Surgery or stereotactic radiosurgery can be done as early as the next day, or may be delayed up to a week to ten days if surgery is planned, or even longer if stereotactic radiosurgery is planned.
CAN I HAVE AN MRI SCAN AFTER AN AVM EMBOLIZATION, SURGERY AND SRS?
The coils, particles, and glues used during embolization are not magnetic and you may have an MR scan after this procedure, and it is routine to do one. The clips used during surgery generally do not interfere with MR imaging, but you should check with the doctor who does the surgery.
WHAT SHOULD I BRING WITH ME THE DAY OF THE PROCEDURE?
Bring an accurate list of your medications, and the names, addresses, and phone numbers of your primary care physicians and any doctors you want us to send the report to. Hand carry any x-ray, CT, MRI or angiogram studies you have had in the past. You take these back with you at the end of the procedure. Do not leave the hospital without them.
WHAT SHOULD I DO THE MORNING OF THE PROCEDURE IN REGARDS TO MEDICATION AND FOOD?
If you are having a general anesthetic, you should not eat or drink anything after midnight before the day of your procedure. If you do eat or drink the anesthesiologist will cancel your procedure.
You should take your regular medications, especially medications for high blood pressure. If you are on aspirin or Plavix, it is okay to take them as regularly scheduled. If you take Glucophage, you should not take it the day of your procedure or for the next two days. If you are on coumadin (Warfarin) let us know. We generally will have you stop it three days ahead of your procedure, but in certain cases will do the study while you are taking that medicine.
HOW CAN I CONTACT YOU AFTER THE EMBOLIZATION PROCEDURE IS PERFORMED AND I HAVE LEFT THE HOSPITAL?
Prior to the patients being discharged from the hospital we will give you instructions for follow-up. During the day we can be reached at 503-494-7736.
If it is after hours please call the paging operator at 503-494-9000 and ask for the Neurointerventional services or the Neurosurgeon on call to be paged.
If it is an emergency go to the nearest emergency room.
