Brain AVM (Arteriovenous Malformation): Symptoms, Causes, and Treatment
Updated: 2 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026
Quick answer
A brain AVM (arteriovenous malformation) is a rare tangle of abnormal blood vessels that shunts blood from arteries straight into veins. It can cause seizures, headaches and weakness, but in about 50% of cases the first sign is brain bleeding. The yearly bleeding risk is around 2% to 3%. Treatment includes surgery, embolization, radiosurgery or monitoring for low-risk AVMs. [1] [2]
What the research says
According to PubMed:
Treatment outcomes vary by method. A meta-analysis of 16 studies (6,124 patients) with unruptured brain AVMs found microsurgery had the highest obliteration rates (99% for Spetzler-Martin grade I-II, 86% for grade III) and the lowest hemorrhage risk (0.6%/yr for grade I-II, 1.3%/yr for grade III). Radiosurgery was moderately effective (76% obliteration for grade I-II, 47% for grade III-IV), and conservative management carried a 1.9-2.6%/yr hemorrhage risk (Ogolo et al., DOI).
Intervention vs. observation. In a single-center cohort of 220 patients (108 ruptured, 112 unruptured), 10-year hemorrhage-free survival was 66% with observation versus 93% with intervention, with annual follow-up hemorrhage rates of 3.2% and 0.4%, and no worse functional outcomes (Koyanagi et al., DOI).
AVMs and hereditary hemorrhagic telangiectasia (HHT). A systematic review of 91 surgically treated patients with HHT-associated brain AVMs found a pooled incidence of new permanent neurological deficits of 9.9%, with no significant difference from sporadic AVM cohorts, although the small sample size precludes definitive conclusions (Buvala et al., DOI).
Study details are from PubMed abstracts.
What is a brain arteriovenous malformation?
An arteriovenous malformation (AVM) is a tangle of blood vessels that creates irregular connections between arteries and veins in the brain. Arteries carry oxygen-rich blood from the heart to the brain, while veins carry oxygen-depleted blood back to the lungs and heart. An AVM disrupts this vital circulation [1].
Arteriovenous malformations can develop anywhere in the body, but the most common locations are the brain and spinal cord. Overall, brain AVMs are rare [1].
The cause of brain AVMs is not clear. Most people who have them are born with them — they form during a baby's growth in the womb. However, they can also form later in life. Rarely, an AVM is a trait passed down in families [1].
Some people with brain AVMs experience symptoms such as headaches or seizures. Others never have symptoms, and the AVM is discovered on a brain scan done for an unrelated issue. Sometimes an AVM is found only after the blood vessels burst and bleed, known as a hemorrhage. Once diagnosed, a brain AVM can be treated to prevent complications such as brain damage or stroke [1].
How a brain AVM changes blood flow
Normally, the heart sends oxygen-rich blood to the brain through arteries. The arteries slow blood flow by passing it through a series of smaller and smaller vessels. The smallest vessels, called capillaries, slowly deliver oxygen through their thin, porous walls to the surrounding brain tissue. The oxygen-depleted blood then passes into small vessels and larger veins, which return it to the heart and lungs [1].
The arteries and veins in an AVM lack this supporting network of capillaries. Instead, blood flows quickly and directly from the arteries to the veins. Because the flow is so fast, surrounding brain tissue cannot absorb enough oxygen [1].
What are the symptoms of a brain AVM?
In some people, a brain AVM causes no symptoms until it bursts and bleeds (hemorrhage). In about half of all brain AVMs, a hemorrhage is the first sign of the malformation. When symptoms do occur before bleeding, they typically include seizures, headaches or pain in one area of the head, and muscle weakness or numbness in one part of the body [1].
Some people experience more serious symptoms depending on where the AVM is located in the brain. These include a very bad headache, weakness, numbness or paralysis, vision loss, trouble speaking, confusion or difficulty understanding others, and trouble walking [1].
Symptom | What it can look like | Why it matters |
Seizure | Sudden convulsions or loss of awareness | Often the first sign before any bleeding |
Headache | Pain in one area of the head; a very bad headache in some cases | New or changing headaches warrant prompt evaluation |
Muscle weakness or numbness | On one side or one part of the body | Signals the AVM is affecting brain tissue |
Vision loss | Changes or loss of sight | Depends on AVM location near visual areas |
Trouble speaking | Slurred or hard-to-find words; difficulty understanding others | Points to language centers being affected |
Trouble walking | Unsteadiness or balance problems | Can mimic stroke-like symptoms |
When to seek emergency care: A bleeding brain AVM is dangerous and requires emergency medical care. Get medical help right away if you notice seizures, severe headaches, or any of the symptoms listed above [1].
When symptoms typically appear
Symptoms of a brain AVM can begin at any age, but they usually appear between ages 10 and 40. An AVM can damage brain tissue over time — the effects build slowly and often cause symptoms in early adulthood. By middle age, however, brain AVMs tend to remain stable and are less likely to cause symptoms [1].
What causes a brain AVM?
The exact cause of brain AVMs is not known. Researchers believe most are present at birth and form during a baby's growth in the womb, though they can also develop later in life [1].
Brain AVMs are seen in some people who have hereditary hemorrhagic telangiectasia (HHT), also called Osler-Weber-Rendu syndrome. HHT affects how blood vessels form in several areas of the body, including the brain [1].
What are the risk factors?
Anyone can be born with a brain AVM, but two factors may raise the risk [1].
Risk factor | How it raises risk |
Being male | Brain AVMs are more common in men |
Family history | Brain AVMs rarely occur in families; a specific genetic risk factor is not clear, but inherited conditions such as HHT can raise risk |
What complications can a brain AVM cause?
The complications of a brain AVM mostly stem from bleeding, disrupted oxygen flow, and vessel damage [1].
Bleeding in the brain (hemorrhage). An AVM puts extreme pressure on the walls of the affected arteries and veins, making them thin or weak, and it may break open and bleed into the brain. The risk ranges from around 2% to 3% each year, and may be higher for certain AVM types and in people who have bled before. Studies have not found that pregnancy increases hemorrhage risk, but more research is needed. Brain AVMs account for about 2% of all hemorrhagic strokes each year, and are often the cause of brain hemorrhage in children and young adults [1]
Reduced oxygen to brain tissue. Blood rushes quickly past the missing capillary network, so surrounding tissue cannot easily absorb oxygen. Tissue can weaken or die off, causing stroke-like symptoms such as trouble speaking, weakness, numbness, vision loss, or unsteadiness [1]
Aneurysm formation. Extreme pressure on thin, weak vessel walls can cause a bulge called an aneurysm, which may be at risk of bursting [1]
Brain damage. The body may grow more arteries to supply the fast-flowing AVM, so some AVMs enlarge and compress nearby brain. This can block protective fluid flow; if fluid builds up, it pushes brain tissue against the skull [1]
Vein of Galen AVM in babies
The vein of Galen type involves a major blood vessel and causes serious complications in babies. Symptoms are present at birth or appear soon after, including fluid buildup in the brain, head swelling, swollen scalp veins, seizures, failure to thrive, and congestive heart failure [1].
How is a brain AVM diagnosed?
To diagnose a brain AVM, a healthcare professional reviews symptoms and conducts a physical exam. Imaging tests are usually performed by radiologists trained in brain and nervous system imaging, known as neuroradiologists [2].
Test | How it works | What it shows |
Cerebral angiography (arteriography) | A thin catheter is threaded from a groin or wrist artery to the brain; dye is injected and vessels are imaged with X-rays | The most detailed test; reveals the feeding arteries and draining veins critical to planning treatment |
CT scan / CT angiography | A series of X-rays creates cross-sectional brain images; dye in a vein highlights vessels | Detailed brain structure; feeding arteries and draining veins viewed in greater detail |
MRI / MR angiography | Powerful magnets and radio waves create detailed images; dye may be injected to view circulation | More sensitive than CT; shows subtle tissue changes, exact AVM location, and any related bleeding |
How is a brain AVM treated?
The main goal of treatment is to prevent hemorrhage (bleeding). Treatment can also help control seizures and other brain symptoms. The right approach depends on your age, health, and the size and location of the AVM. Medicines may be used to treat AVM-related symptoms such as headaches or seizures [2].
Surgical removal (resection)
Surgery may be recommended if the AVM has bled or sits in an easily reached area. The surgeon removes part of the skull, seals off the AVM with special clips under a high-powered microscope, and carefully removes it from surrounding tissue before reattaching the skull. Resection is usually done when removal carries little risk of hemorrhage or seizure. AVMs in deep brain regions carry higher complication risk, so other treatments may be recommended [2].
Endovascular embolization
A catheter is inserted into an artery in the leg or wrist and threaded to the brain with X-ray guidance. Positioned in a feeding artery, it delivers an embolizing agent — small particles, a gluelike substance, microcoils, or other materials — that blocks the artery and reduces blood flow into the AVM. This approach is less invasive than traditional surgery. It may be performed alone, but is often used before other surgical treatments to shrink the AVM or lower bleeding likelihood. In some large AVMs, it can reduce stroke-like symptoms by redirecting blood back to brain tissue [2].
Stereotactic radiosurgery (SRS)
Precisely focused radiation — many targeted beams converging on the AVM — damages the abnormal vessels and causes scarring. The scarred vessels then slowly close over 1 to 3 years. No cuts in the body are needed. SRS may be done for small AVMs that are hard to remove with traditional surgery, or for AVMs that have not caused dangerous hemorrhages [2].
Monitoring
Sometimes doctors choose to monitor a brain AVM rather than treat it. This may be recommended when there are few or no symptoms, or when the AVM sits in a hard-to-treat area. Monitoring includes regular checkups with the care team [2].
Treatment | How it works | Best suited for |
Surgical resection | Remove part of the skull, clip and remove the AVM | AVMs that have bled or are easily reached, with low complication risk |
Endovascular embolization | Catheter delivers particles or a glue-like agent to block the feeding artery | Less invasive; alone or before other surgery to shrink the AVM; can redirect blood in large AVMs |
Stereotactic radiosurgery | Focused radiation beams scar and close vessels over 1–3 years | Small AVMs hard to reach surgically, or those without dangerous bleeds |
Monitoring | Regular checkups without treatment | Few or no symptoms, or AVM in a hard-to-treat location |
Potential future treatments
Researchers are working to better predict hemorrhage risk in people with brain AVMs by studying AVM features seen on imaging and inherited conditions linked to AVMs, such as HHT. New imaging tools — advanced MRI techniques and 3D models — could help visualize the AVM and nearby tissue to improve surgical precision and safety. Ongoing advances in embolization, radiosurgery, and microsurgery are also making previously hard-to-access AVMs safer to treat [2].
How can you cope and find support after a brain AVM diagnosis?
A brain AVM diagnosis can be overwhelming, but several steps can help [2].
Learn about your AVM: ask your healthcare professional about its size and location and how that affects your treatment options
Accept your emotions: complications such as hemorrhage and stroke bring emotional as well as physical concerns, and some mood changes may be caused by the injury itself
Keep friends and family close: strong relationships provide both practical support and encouragement
Find someone to talk with: a friend, family member, counselor, medical social worker, clergy member, or support group; national organizations such as the American Stroke Association and the Aneurysm and AVM Foundation can help you find support groups
How should you prepare for a brain AVM appointment?
A brain AVM may be diagnosed in an emergency right after bleeding, found after other symptoms prompt a brain scan, or discovered during diagnosis or treatment of an unrelated condition — often leading to a referral to a neurologist or neurosurgeon [2].
Write down your symptoms, including any that seem unrelated [2]
List all medicines, vitamins, and supplements [2]
Ask a family member or friend to come along [2]
Prepare questions: What are other possible causes of my symptoms? What tests will confirm the diagnosis? What are my treatment options and the pluses and minuses of each? What results can I expect? What kind of follow-up should I expect? [2]
Your doctor will likely ask when symptoms started, whether they are continuous or occasional, how severe they are, and what seems to improve or worsen them. In the meantime, avoid any activity that may raise blood pressure and stress an AVM — such as heavy lifting or straining — and avoid taking blood-thinning medicines such as warfarin unless your doctor advises otherwise [2].
What is the bottom line on brain AVMs?
A brain arteriovenous malformation is a rare but important condition: most people never know they have one until symptoms appear, and in about half of cases the first sign is bleeding. Knowing the symptoms — seizures, one-sided headaches, weakness or numbness — and seeking prompt care can prevent the most serious outcomes. Modern diagnosis relies on detailed imaging, and treatment spans three complementary approaches: surgical removal, catheter-based embolization, and focused radiosurgery, with careful monitoring a valid option for low-risk AVMs [1] [2].
Next steps: Talk with a healthcare professional if you or someone you love has experienced seizures, unusual headaches, or sudden one-sided weakness or numbness. Early evaluation matters. For sudden severe headache, weakness, or loss of speech or vision, call 911 or your local emergency number.
Frequently asked questions
What are the symptoms of a brain AVM?
Symptoms can include seizures, headaches or pain in one area of the head, and muscle weakness or numbness in one part of the body. Depending on location, more serious symptoms may occur — very bad headaches, weakness or paralysis, vision loss, trouble speaking, confusion, or trouble walking. In about half of all brain AVMs, the first sign is a hemorrhage (bleeding in the brain), which is an emergency [1].
Is a brain AVM dangerous?
An AVM carries an ongoing risk of bleeding — around 2% to 3% each year — with higher risk after a previous bleed. A hemorrhage can damage brain tissue, and reduced oxygen flow can cause stroke-like symptoms. Because a bleeding AVM is an emergency, prompt medical evaluation and treatment can help prevent serious complications such as brain damage or stroke [1] [2].
How is a brain AVM treated?
Treatment depends on age, health, and the AVM's size and location. The three main options are surgical removal (resection), endovascular embolization (blocking the feeding artery with a catheter), and stereotactic radiosurgery (focused radiation that closes the vessels over 1 to 3 years). Some low-risk AVMs are simply monitored with regular checkups [2].
Can you live with a brain AVM without treatment?
Yes — monitoring is an option when an AVM causes few or no symptoms, or sits in a hard-to-treat area. Your care team can weigh the yearly bleeding risk against treatment risks. In the meantime, avoid heavy lifting or straining and blood-thinning medicines such as warfarin unless your doctor says otherwise [2].
What causes a brain AVM?
The exact cause is not known. Most brain AVMs are present at birth and form during growth in the womb, though they can also form later in life. Brain AVMs are more common in men, and rarely run in families — certain inherited conditions, such as hereditary hemorrhagic telangiectasia (HHT), can raise the risk [1].
This article is educational and is not a substitute for professional medical advice, diagnosis, or treatment. If you have a sudden, severe headache, seizure, or new weakness, seek emergency care immediately.
Related Reading
Learn more in our guide to CT Angiogram (CTA): What It Shows, How to Prepare and What to Expect.
MRA (Magnetic Resonance Angiography): What It Is, Why It's Done, Procedure and Results explains how magnetic resonance angiography makes detailed pictures of your blood vessels without X-ray radiation.
Functional MRI (fMRI): What It Shows, How It Works and How to Prepare explains how functional MRI maps important brain areas before surgery.
Cerebral Angiogram: What It Shows, How to Prepare, What to Expect, Risks and Recovery explains how a catheter and contrast dye show the brain's blood vessels, how to prepare and the risks.
References
Mayo Clinic Staff. Brain AVM (arteriovenous malformation) - Symptoms and causes. Mayo Clinic. May 29, 2026. https://www.mayoclinic.org/diseases-conditions/brain-avm/symptoms-causes/syc-20350260
Mayo Clinic Staff. Brain AVM (arteriovenous malformation) - Diagnosis and treatment. Mayo Clinic. May 29, 2026. https://www.mayoclinic.org/diseases-conditions/brain-avm/diagnosis-treatment/drc-20350265
Ogolo D, et al. Comparative treatment outcomes of management modalities for unruptured brain arteriovenous malformations: a systematic review and meta-analysis of 6,124 patients. Neurol Res. 2026. PMID 42826096. https://doi.org/10.1080/01616412.2026.2741676
Koyanagi M, et al. Intervention versus observation for brain arteriovenous malformations: long-term hemorrhagic outcomes in a single-center cohort study. J Neurointerv Surg. 2026. PMID 42728087. https://doi.org/10.1136/jnis-2026-025581
Buvala J, et al. Permanent neurological morbidity after microsurgical resection of hereditary hemorrhagic telangiectasia-associated brain arteriovenous malformations: a systematic review and illustrative case. Brain Spine. 2026;6:107455. PMID 42830897. https://doi.org/10.1016/j.bas.2026.107455
National Institute of Neurological Disorders and Stroke. Arteriovenous Malformations (AVMs). National Institute of Neurological Disorders and Stroke. Last reviewed March 13, 2026. https://www.ninds.nih.gov/health-information/disorders/arteriovenous-malformations-avms
American Association of Neurological Surgeons. Arteriovenous Malformations. AANS. April 4, 2024. https://www.aans.org/patients/conditions-treatments/arteriovenous-malformations/
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