Brain Arteriovenous Malformation (AVM)
An arteriovenous malformation (AVM) is a tangle of abnormal blood vessels in the brain or spinal cord. Blood flows directly from arteries to veins, without passing normally through small capillary vessels. The veins from an AVM are often enlarged and contain arterialized (red) blood under increased pressure.
An AVM can occur anywhere in the brain, including the brainstem. They may develop on the surface or be deep inside. They can be large or very small. AVMs may have aneurysms on the blood vessels going to or inside them. An aneurysm-like outpouching called a varix can occur on one of its draining veins.
Because of its altered blood flow, the brain tissue right around an AVM may not get enough oxygen. A brain AVM may produce seizures or other neurological symptoms. It may rupture (bleed) into an area of its surrounding brain or into the spinal fluid cavities (ventricles).
The risk for a first hemorrhage from an AVM is felt to be about 1–3% per year. The risk of death related to a bleed is 10–15% and the chance for a permanent neurological problem is up to 30%. The risk for a repeat hemorrhage is increased, especially in the first 6–12 months. With hemorrhage into the brain, normal brain tissue is damaged, which can result in temporary or permanent loss of normal function.
On the other hand, some AVMs will never bleed. Others may be asymptomatic, only to be discovered by accident on a brain imaging study done for another reason.
Signs and Symptoms
Some AVMs may never produce any symptoms. When an AVM becomes symptomatic, it is most often due to a hemorrhage (bleed) or seizure. In general, hemorrhage from an AVM may present with headache, nausea, vomiting, loss of consciousness, seizure or loss of neurological function (such as weakness or difficulties with speech or vision). The severity of the symptoms are related to the size and location of the hemorrhage. Patients who experience a seizure may develop epilepsy.
The exact cause of an AVM is not known. Although they are not inherited, most are likely present from birth.
A brain AVM is often diagnosed during evaluation for a brain hemorrhage or seizure. It may also be discovered by accident on brain imaging studies obtained to investigate some other condition. Common tests used in the diagnosis and evaluation of an AVM include computerized tomography ( CT ) [which may lead to a CT angiogram ( CTA )], magnetic resonance imaging ( MRI ), functional MRI ( fMRI ), cerebral angiogram and electroencephalogram ( EEG ).
Treatment of an AVM can be challenging. The decision to treat is complex. Our specialized neurosurgeons and neuro-interventionalists at Goodman Campbell work together as a team to recommend the best choices for you.
Many factors including your age, general health, history of hemorrhage, as well as the size, location and architecture of your AVM are taken into consideration. One or more options may be considered:
- Observation may be recommended following careful consideration of many factors. Essentially, the main reason to consider treatment of an AVM is to prevent the risk of bleeding. If the risks involved with treatment are higher than the calculated life-long risk associated with hemorrhage from the AVM, observation might represent the better choice.
- Stereotactic radiosurgery (SRS) is a precise type of radiation therapy done as an outpatient procedure. With careful planning and computer assistance, small beams of radiation from different paths intersect at the AVM. The AVM gets a very high dose of radiation while the rest of the brain gets very little. The radiation scars the AVM vessels closed. The risk of a permanent neurological problem from radiosurgery is very small. SRS may cure up to 80% of small AVMs, but less than half of larger ones. SRS may take several years to work. The risk for hemorrhage is not lessened until the AVM is gone. In some instances, your doctors may consider treating individual portions of a larger AVM by using three to five separate treatments given over a period of time.
- Embolization is performed through an angiogram-like technique. A small catheter is used to inject glue-like material into the AVM to seal off its blood flow. Currently, it is difficult to completely obliterate an AVM safely using only embolization. Embolization is typically used when needed alongside surgery or SRS. Embolization includes some risk for stroke or hemorrhage. As with any treatment, the decision to embolize carefully weighs its benefit against any potential risks.
- AVM resection is done through a craniotomy: an open surgical procedure to remove the AVM. A navigation system (similar to GPS), based on your brain imaging studies, is used to map out the AVM and help guide the surgery. A window is made in the skull which is replaced at the end of surgery. The standard risks of craniotomy (such as infection, stroke or hemorrhage) are relatively small. A high-powered microscope is used to aid in the surgical removal of the AVM. Surgery provides the chance for immediate and complete removal of the AVM.
- Anti-seizure medicine is used to prevent further seizures. Sometimes, it may be used for a short period around the time of surgery.
- Therapies In some instances, an AVM and its subsequent treatments may affect your motor skills, speech, swallowing or even cognitive abilities, depending on its size and location. Physical, occupational and speech therapies may be used to help regain or compensate for any diminished abilities. These rehabilitative therapies may be performed in an inpatient or outpatient setting.
Follow-up care includes monitoring of your clinical condition. MRI scans or CTAs may be checked for several years following SRS or embolization treatment to see if the AVM is closing off. Formal angiography is usually done after surgery or at some point following SRS or embolization to confirm that the AVM is no longer filling with blood.