If you or a loved one is experiencing seizures, headaches or cognitive difficulties, you may be concerned about brain arteriovenous malformations (AVMs). Although rare, this vascular abnormality can be severe and life-threatening, so it’s natural to be worried.
Our guide will explain the symptoms of AVM, its causes, and treatment, and why an MRI is a crucial tool in helping your medical team identify and treat an AVM.
What is a Brain Arteriovenous Malformation?
A brain arteriovenous malformation (AVM) happens when the blood vessels in the brain become entangled, resulting in abnormal connections between the arteries and the veins in the brain. This means the capillaries, which normally connect the arteries to the veins, are bypassed.
A brain arteriovenous malformation is a broader term for the abnormality. A cerebral arteriovenous malformation specifically refers to AVMs in the cerebrum, which is the largest part of the brain, while an intracranial arteriovenous malformation refers to AVMs anywhere inside the skull, which can include the brainstem and the cerebellum, as well as the cerebrum.
Your arteries usually carry oxygen-rich blood from the heart to other body parts that need oxygen, including cells, tissues and organs. However, in the case of brain AVM, the bypassed capillaries mean that the brain does not get the oxygen it needs, leading to tissue damage and nerve cell damage over time.
An AVM has three parts: feeding arteries, which supply blood to the AVM; draining veins, which remove it; and the nidus, an abnormal cluster or tangle of blood vessels in between.
People with brain AVMs may not experience any symptoms. However, in some cases, the blood vessels become so weakened that they burst (haemorrhage), causing stroke or brain damage.
AVMs are thought by experts to be present from birth (congenital) and are rare, affecting less than 1% of the population. Haemorrhages caused by AVMs are most likely to happen in people aged 15 to 20, but they can also occur later in life.
What Are the Symptoms of Brain AVMs?
The symptoms of AVMs can be mild to severe and can appear at any age. However, the damage caused by AVMs builds up over time, so they are more likely to appear in the third decade of life when people are in their 20s or older. If symptoms do not appear by the time someone is in their 40s or 50s, the AVM is likely to be stable and unlikely to cause symptoms.
Symptoms associated with AVMs include:
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Seizures: These can be focal, which means they affect only a small part of the brain, or generalised, which means they are widespread. Seizures can cause convulsions, a loss of control in movement or changes in consciousness.
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Headaches: These can vary in intensity, frequency and length and may resemble migraines. They may cause persistent pain in one spot, indicating where the AVM is.
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Pain: Pain can be widespread and not specific to the AVM. If the AVM is located in the spine, a person might experience severe back or leg pain.
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Visual problems: If the AVM is near the optic nerve or in the occipital lobe, it can cause vision loss, problems with eye movement or swelling of the optic nerve.
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Muscle weakness: Specific body parts may be affected by muscle paralysis or weakness.
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Problems with speech: A person with a brain AVM may experience difficulty speaking or even understanding language (aphasia).
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Problems with movement: AVMs in the brainstem or cerebellum can impact coordination, making walking and moving more challenging.
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Abnormal sensations: Some people experience numbness, tingling or spontaneous bouts of pain.
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Cognitive difficulties: These include memory loss or confusion, hallucinations or dementia.
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Dizziness: AVMs can cause damage to the brain stem or cerebellum, causing bouts of dizziness.
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Developmental differences: There may be learning difficulties or behavioural differences in children or teenagers with AVMs, although these can be hard to spot.
Can an MRI Detect an Arteriovenous Malformation?
MRI can clearly show AVMs by detecting fast blood flow patterns, known as flow voids, and changes in neurological tissues. It can also detect complications like bleeding or swelling around the AVM. A special dye called a contrast agent can make these images even clearer, helping doctors diagnose AVMs accurately.
How Do Doctors Diagnose Brain Arteriovenous Malformations?
A doctor will take a comprehensive approach to diagnosing an AVM; each step is crucial to identify and assess its severity accurately. Here’s how they do it.
Medical History and Symptom Review
A clinician or specialist will begin by asking about symptoms, present and history. For example, past seizures are an important symptom of AVMs. They will also take a complete family history, particularly with genetic conditions such as hereditary haemorrhagic telangiectasia (HHT), which increases the risk of AVMs.
Physical and Neurological Examination
Next, a physical and neurological exam checks brain function, including memory, movement and sensations. This can help a doctor locate where the AVM is in the brain.
MRI Scan
An MRI is one of the best tools for diagnosing AVMs because it produces detailed brain images showing the tangled blood vessels typical with AVMs. A contrast-enhanced MRI can also highlight how the AVM interacts with surrounding brain tissue, which helps doctors plan treatment.
CT Scan
While MRIs are effective, CT scans are often used first, especially in emergencies. A CT scan can quickly detect bleeding in the brain, though it won't show the blood vessels as clearly as an MRI. A CT angiogram (CTA) uses a contrast dye to highlight the feeding arteries and draining veins to and from the AVM.
Cerebral Angiography (Digital Subtraction Angiography, DSA)
This is the most accurate test for AVMs. It involves injecting dye into the blood vessels to get a detailed map of the AVM and identify its size, location and connections. This type of information is crucial for the specialist planning treatments, such as surgery or embolisation.
Magnetic Resonance Angiography (MRA)
MRA is a non-invasive way to see the brain’s blood vessels. It helps detect AVMs in people who can’t undergo invasive procedures.
CT Angiography (CTA)
CTA combines a CT scan with contrast dye to show blood vessels quickly. It’s helpful in emergencies to check for bleeding and see the AVM’s structure.
Electroencephalogram (EEG), If Seizures Are Present
An EEG can check the brain’s electrical activity, link seizures to the AVM, and help your doctor decide on the right treatment.
What Other Coditions Might Oresent as AVMs (Differential Diagnosis)?
AVMs can present with various symptoms and imaging characteristics that can overlap with other vascular and non-vascular lesions, including:
Brain aneurysms
A bulging blood vessel. Angiography and MRI can help distinguish aneurysms from AVMs by showing the different shapes and structures.
Venus malformation
These are abnormal veins without high blood flow or arterial involvement. MRI and DSA can confirm the absence of arterial connections, unlike in AVMs.
Cavernous hemangiomas
These are clusters of dilated vessels, often causing symptoms similar to AVMs, such as seizures, headaches or bleeding. MRI is effective at diagnosing cavernous hemangiomas due to their popcorn-like structure.
Developmental Venous Anomalies (DVAs)
DVAs are characterised by a collection of small veins draining a region of the brain, but they don’t usually come with arterial malformations. They are generally benign and don't require any treatment. MRI and MRA can identify DVAs from AVMs by looking at the drainage patterns and connections.
Brain tumours
Some tumours mimic AVMs with high blood supply and similar symptoms, but MRI and CT scanning can reveal features specific to tumours.
What Causes an Arteriovenous Malformation?
The exact cause of AVMs isn’t well understood, but they are often present at birth. Some AVMs may be inherited. However, most cases are linked to other inherited conditions that increase the risk of developing an AVM.
Vascular problems, like AVMs, are thought to result from issues during development in the womb, where blood vessels form and disappear as the fetus grows. Problems with the chemicals that control blood vessel growth may cause AVMs and other vascular issues. Some AVMs are linked to genetic mutations, and a few are hereditary, while others may develop later in life when the central nervous system is injured.
Changes in blood flow and pressure can affect the growth and development of AVMs. Increased blood flow and pressure can cause existing AVMs to grow larger or new ones to form. For example, certain surgeries like the Fontan operation, which changes blood flow patterns, can lead to the development of AVMs.
Although most AVMs are present from birth, certain environmental factors can make them worse or cause new ones to form. Trauma or surgeries can sometimes trigger the development of AVMs in blood vessels that were previously normal.
Certain hereditary vascular conditions increase the risk of developing AVMs, such as HHT, Sturge-Weber syndrome, and Klippel-Trenaunay syndrome.
Prognosis and Treatment For AVMs
The outlook and treatment for people with AVMs can be complex and depend on factors such as the size and location of the AVM, what symptoms are present, and whether the ACM has ruptured.
If it has ruptured, there is a higher risk of severe complications and death due to bleeding in the brain. The risk of bleeding is low for unruptured AVMs, but it increases significantly if the AVM ruptures. Research, like the ARUBA trial (2015), shows that people with unruptured AVMs who are monitored rather than treated right away may have better outcomes.
There is a range of treatment options for people with AVMs:
Managing symptoms only and monitoring: This is especially helpful for older patients or patients with health problems who have unruptured AVMs. Treatment may involve monitoring and managing symptoms, such as seizures, without surgery.
Surgery: This is often the first line treatment for AVMs because of the risk of the AVM rupturing and causing significant complications. Surgeons will enter the brain and remove the central part of the AVM while keeping as much of the surrounding tissue in tact as possible. Surgery does carry risks like bleeding and brain injury, so your doctor will carefully explain these before you consent to surgery.
Endovascular embolisation: Often used alongside surgery, this minimally invasive treatment involves a specialist guiding a catheter through an artery to the AVM. The surgeon then injects the AVM with a substance that will create an artificial blood clot in the centre of the AVM, reducing blood flow through the AVM and making surgery safe.
Radiosurgery: This involves using focused radiation to gradually shrink or destroy the AVM, especially if surgery is too risky. However, it can take time for the AVM to disappear completely.
Sometimes, clinicians will combine these approaches to shrink or eliminate the AVM.
Why is an MRI Scan a Good Option for AVMs?
MRI is a crucial tool for detecting AVMs in the brain, as it provides detailed images of soft tissues and blood vessels without the need for harmful radiation. It is one of the most effective methods for diagnosing AVMs, as it clearly shows the tangled blood vessels characteristic of these malformations. When enhanced with contrast dye, MRI can also reveal how the AVM affects nearby brain tissue, helping your doctor to develop the right treatment plan for you.
How Does an MRI Scan Detect an Arteriovenous Malformation?
MRI uses powerful magnets and radio waves to create detailed images of the body’s internal structures without harmful radiation. It relies on the magnetic properties of hydrogen atoms in your body's water molecules, which align when exposed to a magnetic field. When the MRI machine applies radiofrequency pulses, these water molecules shift and emit signals as they return to their original place. These signals create the images you’ll see in your MRI results.
MRI can identify the abnormal blood vessels associated with AVMs by highlighting unique features. For example, one of the key indicators of an AVM on an MRI is ‘flow voids’. These darks areas on the scan occur because the blood is moving so quickly that it doesn't produce enough signal for the MRI to capture, making the vessels appear black.
When contrast agents are used, they also help make the vessels stand out more clearly, allowing doctors to see the tangled blood vessels and veins that indicate an AVM.
Find an MRI Scan for an Arteriovenous Malformation
If you’re worried that you or a loved one have symptoms of AVM, you can book a private MRI scan today, including a head and brain MRI. If you’re unsure whether an MRI is suitable for you, one of our expert clinicians is available for a personalised consultation. They can discuss your symptoms and concerns and help you decide what to do next.
Sources:
Arteriovenous Malformations (AVMs) (N.D.) https://www.ninds.nih.gov/health-information/disorders/arteriovenous-malformations-avms
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Brain Arteriovenous Malformations. (2023). https://www.msdmanuals.com/home/brain-spinal-cord-and-nerve-disorders/stroke/brain-arteriovenous-malformations-avms
Chen, C.J., et al. (2020). Brain arteriovenous malformations: A review of natural history, pathobiology, and interventions. https://pubmed.ncbi.nlm.nih.gov/33004601/
Derdayn, C. P., et al. (2017). Management of Brain Arteriovenous Malformations: A Scientific Statement for Healthcare Professionals From the American Heart Association/American Stroke Association. https://www.ahajournals.org/doi/10.1161/str.0000000000000134
Differential diagnosis — Arteriovenous malformation. (2021). https://www.compva.com/science/differential-diagnosis-arteriovenous-malformation
Mohr, J. P., et al. (2015). Medical management with or without interventional therapy for unruptured brain arteriovenous malformations (ARUBA): a multicentre, non-blinded, randomised trial. https://pmc.ncbi.nlm.nih.gov/articles/PMC4119885/
Scherschinski, L., et al. (2022). Genetics and Emerging Therapies for Brain Arteriovenous Malformations. https://www.sciencedirect.com/science/article/abs/pii/S1878875021016247
