What Causes a Brain Aneurysm (AVM)?

And what, specifically, is an “AVM”?

Arteriovenous malformations (AVM) are the atypical formations of blood vessel connections that bridge arteries and veins. These abnormal connections are often described as “tangles” and may look similar to a bird’s nest. The malformations may originate in the artery, the vein, or the capillaries which bridge your artery and vein. In some cases, the capillary is missing altogether, also leading to arteriovenous entanglement. 

AVMs can occur anywhere in the body (peripheral AVMs) but are most commonly found in or on the surface of the brain and spinal cord. Because our arteries and veins are responsible for transporting oxygen and nutrient-rich blood throughout the body, having healthy blood vessel connections is vital to supporting a healthy brain and spinal cord. 

Brain AVMs are generally stable, but can dilate (or expand) over time. Physicians might categorize your AVM using a specific scaling system that describes the size, sounds, and impact of an arteriovenous malformation. 

Brain AVMs are officially diagnosed using various imaging techniques including computed tomography (CT), computed tomography angioplasty (CTA), magnetic resonance imaging (MRI), cerebral magnetic resonance angiography (MRA), ultrasound (US), transcranial doppler, or catheter angiogram. 

Risk Factors and Causes of Brain AVMs

Approximately less than 1% of the U.S. population is thought to have arteriovenous malformation. Typically, AVMs are congenital, meaning that they are present at birth. A very small proportion are believed to be hereditary, or passed down by family members. Rarely, AVMs may develop after a traumatic injury or infection. 

People are most often diagnosed with a brain AVM in their 20s to 40s during incidental testing and imaging for other concerns or conditions. The highest risk of complications occurs in adults in their 40s and 50s. Arteriovenous malformations appear to affect males more often than females. People with uncontrolled blood pressure, who smoke or use tobacco, or with substance use issues appear at a higher risk for developing complications of AVMs.

Symptoms of Brain AVMs

People usually do not experience symptoms and may not be aware that they have AVMs. However, an estimated 12% of people with AVMs may experience symptoms that can vary greatly in type and severity. When experienced, commonly reported symptoms of AVM can include:

  • Head pain or headaches that may vary in frequency, duration, or pattern. They may be felt on a single side or wrap around the head.
  • Seizures that may be focal or generalized with or without loss of consciousness and may vary in frequency, duration, or pattern. No specific types or patterns of seizure are specifically associated with AVM.
  • Neuromotor changes or abnormalities in strength, coordination, or sensation in parts of your body or with your typical movements.
  • Changes in vision or oculomotor coordination which may result in blurred vision, double vision, or other visual perception challenges.
  • Experiencing nausea, vomiting, or dizziness.
  • Difficulty speaking which may include producing works, slurred speech, comprehending what others are saying, and more.
  • Cognitive changes or challenges including memory, learning difficulties, losses of consciousness, or confusion.

If you experience any of these signs of AVM, you should share these symptoms with your provider. If you notice an acute, sudden onset or change in symptoms, consider contacting Morrison Clinic immediately.

Brain Aneurysms and AVM Complications

There are some very serious risks for complications with brain AVMs, including stroke, brain bleed, and aneurysms. Some experts estimate approximately 50% of brain or spinal cord AVMs result in an aneurysm. 

To maintain the blood flow through the vessels of an arteriovenous malformation, there is an increase in blood pressure within the vessels to push the blood through the tangled connection. This increased pressure can strain the blood vessel walls and can ultimately result in a bulge, or ballooning, at a weak point of a blood vessel wall. This bulging area is called an aneurysm, or brain aneurysm when occurring in or on the brain.

Brain aneurysms can often be small without causing any issues. However, brain aneurysms are life-threatening if they rupture. This rupture, and the resulting brain bleed or hemorrhage, can cause tremendous and potentially fatal brain damage. Immediate medical attention is needed to perform life-saving interventions and to maximize and preserve recovery potential.

Signs and Symptoms of a Brain Aneurysm AVM

Brain bleeding is the first reported symptom in approximately 50% of people with AVM brain aneurysms. So, it is particularly important to be aware of all of the signs and symptoms. A ruptured brain aneurysm is often described by patients as an immediate, excruciating headache. Other signs and symptoms of a ruptured brain aneurysm can include:

  • Sudden, extremely severe headache
  • Nausea and vomiting
  • Stiff neck
  • Blurred or double vision
  • Sensitivity to light
  • Seizure
  • A drooping eyelid
  • Loss of consciousness
  • Confusion

Seek medical attention immediately with Morrison Clinic if you experience any of the signs. Brain aneurysms may also leak blood before rupturing but often still produce severe headaches or other related symptoms. Someone with a brain aneurysm that is not leaking and unruptured may experience no symptoms at all. However, if the unruptured brain aneurysm is large enough, it may disrupt surrounding tissues or nerves leading to some of the following symptoms:

  • Pain above and behind one eye
  • A dilated pupil
  • Change in vision or double vision
  • Numbness on one side of the face

Again, if you experience any of these signs of AVM, you should share any of these symptoms with Dr. Morrison. If you notice an acute, sudden onset or change in symptoms, consider seeking medical care immediately.


Treatment options vary based on specific patient needs, as well as the severity or status of the AVM or AVM brain aneurysm. Interventions typically focus on stopping a bleeding aneurysm, treating symptoms of an AVM, or bypassing an AVM to prevent future problems. Common AVM and brain aneurysm treatment approaches include:

  • Medications to reduce headaches, seizures, or other neurological symptoms
  • Embolization, sclerotherapy, and stereotactic (Gamma Knife) radiosurgery to manage and reduce AVM size
  • Microvascular clipping, endovascular coiling  or liquid embolic placement to stop brain bleeding

Dr. Morrison will provide you with more specific information about each treatment approach and your individual options.

The Aneurysm Experts at Morrison Clinic™ 

Morrison Clinic™ is your South Florida expert for providing arteriovenous malformation and aneurysm care. Our practice includes our Palm Beach County-based neurosurgery center with six clinics located conveniently throughout South Florida. Dr. John F. Morrsion, MD, founder and leader of Morrison Clinic™, is a fifth-generation physician and an expert neurosurgeon who takes pride in using his research and practice experience to transform the quality of life of his patients with spinal conditions. After attending medical school at Creighton University, he completed his general surgery internship at Boston University and subsequently his neurosurgery residency and fellowship training at Brown University and the University at Buffalo.

Dr. Morrison is widely respected by his peers and highly recommended by his patients. Morrison Clinic™ offers excellence in high-quality interventions to safely and effectively treat your AVM and aneurysm concerns. To learn more about what Morrison Clinic™ can do for you, fill out our free virtual consultation form to schedule time with our team.