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PubMed This is a summary of 16 peer-reviewed journal articles Updated
Neurology

Symptoms & Biology of Brain AVMs

At a Glance

A brain AVM is an abnormal tangle of blood vessels that can cause seizures, severe headaches, or neurological issues even without bleeding. If an AVM ruptures, it causes a sudden, severe 'thunderclap' headache that requires immediate emergency care.

Understanding how a brain arteriovenous malformation (AVM) behaves biologically can help explain why you may be experiencing certain symptoms. While many AVMs are “silent” and found only by chance, others make their presence known through neurological changes or a sudden medical event [1][2].

Common Symptoms of an Unruptured AVM

When an AVM has not bled (unruptured), it can still cause symptoms by physically pressing on the brain or by altering the way blood moves through nearby tissue [1].

  • Seizures: This is one of the most common ways an AVM is discovered. Seizures occur because the AVM can irritate the surrounding brain tissue [3]. This risk is higher if the AVM is located in the frontal or temporal lobes [3][4].
  • Headaches: While many people with AVMs have no headaches, others experience chronic, migraine-like pain. Sometimes these headaches are localized to the same side of the head as the AVM [5].
  • Pulsatile Tinnitus: You may hear a “whooshing” or rhythmic thumping sound in your ear that matches your heartbeat. This is the sound of high-pressure blood rushing through the abnormal vessels near the temporal bone [6].
  • Focal Neurological Deficits: These are specific “glitches” in brain function, such as weakness on one side of the body, vision loss, or difficulty speaking. These occur when the part of the brain responsible for those tasks is not receiving enough oxygen or is being compressed [7][8].

The Biology of “Vascular Steal”

You may hear your doctors mention a phenomenon called vascular steal syndrome. This happens because an AVM is a “low-resistance” pathway—it is much easier for blood to rush through the AVM’s tangle than to push through the tiny, narrow capillaries of healthy brain tissue [6][9].

Essentially, the AVM “steals” blood and oxygen away from the healthy parts of the brain nearby [7]. This lack of oxygen (hypoperfusion) can lead to localized “starvation” of brain cells, which may cause progressive memory issues, cognitive changes, or symptoms that feel like a “mini-stroke” (transient ischemic attack) [7][8][10].

Ruptured vs. Unruptured: How They Present

The presentation of an AVM changes dramatically if the thin-walled vessels within it leak or burst.

  • Unruptured AVM: Often presents gradually. You might have a first-time seizure or a slowly worsening headache [1][11]. In many cases, there are no symptoms at all, and it is found during a scan for a different issue [2].
  • Ruptured AVM (Hemorrhage): This is a medical emergency. It often presents with a sudden, “thunderclap” headache—the worst headache of your life [12]. It can be accompanied by sudden nausea, vomiting, a stiff neck, or loss of consciousness [13]. If you experience these symptoms, call 911 immediately—do not drive yourself to the hospital.

How an AVM Differs from Other Vascular Issues

It is easy to confuse an AVM with other brain “spots,” but they are biologically distinct:

Condition Biological Mechanism Hemodynamics
Brain AVM A direct tangle of arteries and veins bypassing capillaries [14]. High-Flow [6]
Cerebral Aneurysm A weak, bulging “bubble” on the wall of a single artery [15]. High-Pressure
Cavernous Malformation A cluster of abnormally dilated small vessels (capillaries) that look like a “popcorn” or berry [16]. Low-Flow (Static)

Unlike an aneurysm, which is a structural failure of a vessel wall, an AVM is a complex network of misconnected plumbing [14][15]. Because AVMs are high-flow systems, they create more significant changes in the brain’s overall blood pressure and circulation than low-flow cavernous malformations [6].

Return to Home Page

Common questions in this guide

What are the most common symptoms of an unruptured brain AVM?
An unruptured brain AVM can cause seizures, severe headaches, a whooshing sound in the ear called pulsatile tinnitus, or localized weakness. However, many people have no symptoms at all until the AVM is found on a brain scan for another reason.
What is vascular steal syndrome in a brain AVM?
Vascular steal syndrome happens when the AVM diverts blood away from healthy brain tissue. This lack of oxygen can lead to memory issues, cognitive changes, or brief episodes of weakness that feel similar to a mini-stroke.
How do I know if my brain AVM has ruptured?
A ruptured AVM is a medical emergency that typically causes a sudden, extremely severe headache often described as a thunderclap. It may also cause sudden nausea, a stiff neck, or loss of consciousness, and requires a 911 call immediately.
How is a brain AVM different from an aneurysm?
An aneurysm is a weak, bulging bubble on the wall of a single artery. In contrast, a brain AVM is a high-flow tangle of abnormally connected arteries and veins that bypass normal capillaries, creating significant changes in blood pressure and circulation.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Does my AVM show signs of 'vascular steal' on my imaging?
  2. 2.How does the location of my AVM relate to the specific symptoms I am experiencing, such as my headaches or seizures?
  3. 3.Are my seizures considered 'structural epilepsy' caused by the AVM?
  4. 4.Is there any evidence of old, silent bleeding (hemosiderin) on my MRI?
  5. 5.How does an AVM differ from a cavernous malformation or an aneurysm in terms of my specific risk for future hemorrhage?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (16)
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    Predictive factors of epilepsy in arteriovenous malformation.

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    Neuro-Chirurgie 2020; (66(3)):144-149 doi:10.1016/j.neuchi.2019.12.009.

    PMID: 32197972
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    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.

    Mohr JP, Overbey JR, Hartmann A, et al.

    The Lancet. Neurology 2020; (19(7)):573-581 doi:10.1016/S1474-4422(20)30181-2.

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    Predictive factors of epilepsy in a cohort of brain arteriovenous malformation patients with a 5-year follow-up.

    Pirlog BO, Porché M, Kyheng M, et al.

    Revue neurologique 2025; (181(10)):991-997 doi:10.1016/j.neurol.2025.09.007.

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    Seizure predictors and outcome after Onyx embolization in patients with brain arteriovenous malformations.

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    Brain Arteriovenous Malformations and Pregnancy: A Systematic Review of the Literature.

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    World neurosurgery 2023; (177()):100-108 doi:10.1016/j.wneu.2023.06.065.

    PMID: 37355173
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    Enhancing cerebral arteriovenous malformation analysis: Development and application of patient-specific lumped parameter models based on 3D imaging data.

    Zhang B, Chen X, Qin W, et al.

    Computers in biology and medicine 2024; (180()):108977 doi:10.1016/j.compbiomed.2024.108977.

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    18F-Fluorodeoxyglucose Positron Emission Tomography-Magnetic Resonance Monitoring of Brain Metabolic Changes in a Case of Arteriovenous Malformation-Related Steal Phenomenon Symptoms.

    Anglani M, Cecchin D, Cester G, et al.

    World neurosurgery 2019; (126()):276-279 doi:10.1016/j.wneu.2019.02.167.

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    Vascular intracranial malformations and dementia: An under-estimated cause and clinical correlation. Clinical note.

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    Patient-Specific Blood Flow Analysis for Cerebral Arteriovenous Malformation Based on Digital Subtraction Angiography Images.

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    Frontiers in bioengineering and biotechnology 2020; (8()):775 doi:10.3389/fbioe.2020.00775.

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    Steal Phenomenon with Tonsillar Arteriovenous Malformation.

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    Unveiling the domino effect: a nine-year follow-up on pentalogy of central nervous system induced by a large unruptured cerebral arteriovenous malformation: a case report and literature review.

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    Frontiers in neurology 2024; (15()):1365525 doi:10.3389/fneur.2024.1365525.

    PMID: 38846033
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    Management of Brain Arteriovenous Malformations: A Scientific Statement for Healthcare Professionals From the American Heart Association/American Stroke Association.

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    Imaging Characteristics and Endovascular Treatment of Brain Arteriovenous Malformations Mainly Fed by the Posterior Cerebral Artery.

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    Ruptured temporal horn aneurysm associated with Moyamoya collateral vessel coexisting with contralateral arteriovenous malformation - technical note with clinical vignette.

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    The Correlation of Vessel Wall Macrophage Infiltration With Hemosiderin in Arteriovenous Malformations.

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This page provides educational information about brain AVM symptoms and biology. Always consult a neurologist or neurosurgeon if you experience new or worsening neurological symptoms, and call 911 immediately if you suspect a ruptured AVM.

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