AVM Awareness Month: What You Need to Know About Brain AVMs

This article originally appeared in The Neurotransmitter, Dr. Grunch’s weekly newsletter.

Picture a healthy, active 28-year-old. No real medical history. One afternoon she gets the worst headache of her life, the kind that hits like a thunderclap. Within an hour she’s in the ER, and the CT scan shows bleeding in her brain. The cause isn’t a tumor or a stroke from clogged arteries. It’s something she was very likely carrying for years without knowing it: an arteriovenous malformation, or AVM.

October is AVM Awareness Month, so let’s talk about what AVMs are, why they matter, and how we treat them. My goal is for you to walk away feeling informed, not scared.

What exactly is an AVM?

Normally, blood travels from your heart through arteries (high pressure), into tiny capillaries (where the pressure drops and oxygen gets delivered to tissue), and then back to the heart through veins (low pressure).

In an AVM, the capillaries are missing. Arteries plug straight into veins through a tangled knot of abnormal vessels we call the nidus (Latin for “nest”). Without capillaries to absorb the pressure, high-pressure arterial blood slams directly into veins that were never built to handle it [1, 4].

Here’s the analogy I use with patients: imagine hooking a fire hose directly to a garden hose. It might hold for a long time. But that garden hose is under constant strain, and if it ever gives out, it gives out suddenly.

AVMs can occur anywhere in the body, but the ones I deal with as a neurosurgeon are in the brain and, less commonly, the spinal cord. This article focuses on brain AVMs.

How common are they?

AVMs are rare. Studies estimate that roughly 10 to 18 out of every 100,000 people have a brain AVM, with about 1 new case diagnosed per 100,000 people each year [4, 9]. For comparison, brain aneurysms are far more common (see my article from last month).

Most brain AVMs are thought to form during development, which is why we often say people are “born with” them. But they’re not always static. They can change over time, and certain inherited conditions, such as hereditary hemorrhagic telangiectasia (HHT), raise the chance of having one. Most people with an AVM have no family history at all.

What are the symptoms?

Many AVMs cause no symptoms and are found by accident on a scan done for something else. When they do cause problems, the most common first signs are bleeding in the brain (in roughly half or more of symptomatic patients) and seizures (about one-third) [4, 9]. Other symptoms include:

• Headaches, sometimes in one consistent location

• Seizures, especially new seizures in a young adult

• Weakness, numbness, or tingling on one side of the body

• Vision changes, trouble speaking, or problems with balance

• Slowly progressive neurologic problems, which happen when the AVM “steals” blood flow from nearby brain or backs up pressure in the veins

When to call 911: a sudden, severe “worst headache of my life,” a first-time seizure, sudden weakness or numbness, trouble speaking, confusion, or loss of consciousness. Don’t drive yourself and don’t wait it out.

The big question: what’s the risk of it bleeding?

Across the major studies, the overall risk of an AVM bleeding is about 2% to 4% per year [1, 5, 8].

That number changes a lot depending on the individual AVM:

• Never bled before: roughly 1.3% to 2.2% per year [5, 6].

• Already bled once: roughly 4.5% to 4.8% per year, especially in the first few years after the first bleed [5, 6].

• Other higher-risk features: a location deep in the brain, drainage only into deep veins, and an aneurysm sitting on one of the feeding arteries [8].

Those risks add up over a lifetime. If an AVM has a 2% chance of bleeding each year, the odds it bleeds at some point over 30 years is roughly 45%. That’s why a young patient and an 80-year-old patient with the exact same AVM may get very different recommendations.

And a bleed is serious. Some patients recover fully, but others are left with lasting neurologic deficits, and a bleed can be fatal. That’s the risk we’re always weighing against the risk of treatment.

How do we diagnose an AVM?

• CT scan: usually the first test in the ER. It’s fast and great at showing bleeding.

• MRI and MRA: show the AVM’s size, its exact location, and the brain tissue around it.

• Cerebral angiogram: the gold standard. A thin catheter is guided into the brain’s arteries and dye is injected so we can map exactly which arteries feed the AVM and which veins drain it. This roadmap drives every treatment decision [1].

How neurosurgeons grade AVMs

Since 1986, neurosurgeons have used the Spetzler-Martin grading scale to estimate the risk of surgery [7]. It looks at three things:

• Size: smaller than 3 cm, 3 to 6 cm, or larger than 6 cm

• Location: whether it sits in “eloquent” brain, meaning areas that control movement, sensation, language, or vision

• Venous drainage: whether it drains into deep veins

Points add up to a grade from I to V. Lower-grade AVMs (I and II) are usually smaller, on the surface, away from critical areas, and generally safer to remove. Higher-grade AVMs (IV and V) carry much more surgical risk, and we often lean toward other strategies, including observation.

What are the treatment options?

The only way to eliminate the bleeding risk is to completely get rid of the nidus [1]. We have three main tools, and many patients need a combination:

• Microsurgical resection: open surgery (a craniotomy) to remove the AVM. When it’s fully removed, the cure is immediate. It’s often the best option for lower-grade AVMs.

• Endovascular embolization: a catheter is threaded through the blood vessels to the AVM, and a glue-like material is injected to block off feeding vessels. It’s most often used to shrink an AVM or make surgery or radiation safer, and it rarely cures an AVM on its own.

• Stereotactic radiosurgery (such as Gamma Knife): not actually surgery. Focused radiation causes the abnormal vessels to scar and close down gradually, usually over two to three years. It’s a good option for smaller AVMs in deep or critical areas. The catch is that the AVM can still bleed while you wait for it to close.

• Observation (medical management): no procedure. We monitor the AVM and treat symptoms, such as controlling seizures and blood pressure.

If you or someone you love has an AVM, ask to be evaluated at a center that offers all three treatment options (open surgery, endovascular, and radiosurgery) with a team that discusses your case together. That way your recommendation is based on what’s best for you, not on which tool one doctor happens to use.

A quick word about spinal AVMs

Since many of you follow me for spine content: AVMs and related vascular malformations can also occur in and around the spinal cord. They’re even rarer, and they can show up as sudden back pain with weakness or as a slow, progressive loss of leg strength, numbness, and bladder or bowel trouble that is easily mistaken for a more common spine problem. If symptoms don’t match the usual story, imaging of the spinal cord and its blood supply may be needed.

The bottom line

• An AVM is an abnormal tangle where arteries connect directly to veins, skipping the capillaries.

• They’re rare, often present in young adults, and many are found by accident.

• The main danger is bleeding: about 2% to 4% per year overall, higher if it has already bled.

• Treatment options include surgery, embolization, radiosurgery, or careful observation, and the right choice is very individual.

• Sudden severe headache, a first seizure, or new weakness means call 911.

If you’re looking for community and support, organizations like The Aneurysm and AVM Foundation (TAAF), the Niekro Aneurysm & AVM Foundation, and The Bee Foundation offer resources, support groups, and survivor stories.

Share this with someone who needs to read it. Awareness really can save a life.

Betsy Grunch, MD, Board-Certified Neurosurgeon | Ladyspinedoc

References

1. Derdeyn CP, Zipfel GJ, Albuquerque FC, et al. Management of brain arteriovenous malformations: a scientific statement for healthcare professionals from the American Heart Association/American Stroke Association. Stroke. 2017;48(8):e200–e224. doi:10.1161/STR.0000000000000134

2. Mohr JP, Parides MK, Stapf C, et al. Medical management with or without interventional therapy for unruptured brain arteriovenous malformations (ARUBA): a multicentre, non-blinded, randomised trial. Lancet. 2014;383(9917):614–621. https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(13)62302-8/abstract

3. Mohr JP, Overbey JR, Hartmann A, et al. Medical management with interventional therapy versus medical management alone for unruptured brain arteriovenous malformations (ARUBA): final follow-up of a multicentre, non-blinded, randomised controlled trial. Lancet Neurol. 2020;19(7):573–581. https://www.thelancet.com/journals/laneur/article/PIIS1474-4422(20)30181-2/abstract

4. Intracranial Arteriovenous Malformations. StatPearls. Treasure Island (FL): StatPearls Publishing; updated 2025. https://www.ncbi.nlm.nih.gov/books/NBK531479/

5. Gross BA, Du R. Natural history of cerebral arteriovenous malformations: a meta-analysis. J Neurosurg. 2013;118(2):437–443.

6. Kim H, Al-Shahi Salman R, McCulloch CE, et al. Untreated brain arteriovenous malformation: patient-level meta-analysis of hemorrhage predictors. Neurology. 2014;83(7):590–597.

7. Spetzler RF, Martin NA. A proposed grading system for arteriovenous malformations. J Neurosurg. 1986;65(4):476–483.

8. Abecassis IJ, Xu DS, Batjer HH, Bendok BR. Natural history of brain arteriovenous malformations: a systematic review. Neurosurg Focus. 2014;37(3):E7. https://thejns.org/focus/view/journals/neurosurg-focus/37/3/article-pE7.xml

9. Current concepts and perspectives on brain arteriovenous malformations: a review of pathogenesis and multidisciplinary treatment. World Neurosurg. 2021. https://www.sciencedirect.com/science/article/abs/pii/S1878875021011153

10. The Aneurysm and AVM Foundation (TAAF). https://www.taafonline.org

Disclaimer: This article is for educational purposes only and is not medical advice. It does not replace individualized care from a licensed physician. If you have symptoms or questions about your own health, please consult your healthcare provider. If you think you are having a medical emergency, call 911.

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