Brain Arteriovenous Malformation (AVM) – Symptoms and Causes
Overview
Brain arteriovenous malformations (AVMs) are abnormal tangles of blood vessels. These tangles create direct connections between arteries and veins, bypassing normal brain tissue.
These unusual formations disrupt the normal blood flow pattern. This pattern involves arteries delivering oxygen-rich blood to the brain and veins returning oxygen-depleted blood to the heart.
AVMs can develop anywhere in the body but commonly affect the brain and spinal cord. These conditions are considered rare.
Most people with brain AVMs are born with them, though they can occasionally develop later in life. In very uncommon cases, they may be hereditary.
Common symptoms include:
- Headaches
- Seizures
- No symptoms (discovered during imaging for other conditions)
Brain AVMs are often discovered in two main ways. These are during brain scans performed for unrelated health issues or after the malformation ruptures and bleeds (hemorrhage).
When a brain AVM is diagnosed, several treatment options exist to prevent serious complications like brain damage or stroke.
Signs and Symptoms
Brain AVMs often don’t cause symptoms until they rupture and bleed. For about half of people with this condition, bleeding is the first indication that something is wrong.
However, some people experience other symptoms before any bleeding occurs:
- Seizures
- Headaches or pain in a specific area of the head
- Muscle weakness or numbness in one part of the body
Depending on where the AVM is located in the brain, more serious symptoms may appear:
- Severe headache
- Weakness, numbness, or paralysis
- Vision problems
- Speech difficulties
- Confusion or trouble understanding others
- Walking problems
These symptoms typically begin between the ages of 10 and 40. Brain AVMs can gradually damage brain tissue over time, with effects building up slowly and often causing symptoms in early adulthood.
By middle age, these malformations tend to become more stable and less likely to cause new symptoms.
When to Get Medical Help
Seek immediate medical attention if you experience any symptoms that might suggest a brain AVM, such as seizures or unusual headaches.
A bleeding AVM is a medical emergency that requires prompt treatment. Don’t wait to see if symptoms improve on their own, as quick action can prevent serious complications.
Causes
The exact cause of brain arteriovenous malformations (AVMs) remains unknown. Most experts believe these abnormal connections between arteries and veins typically form during fetal development. However, brain AVMs can also develop later in life.
Some brain AVMs occur in people with hereditary hemorrhagic telangiectasia (HHT), also called Osler-Weber-Rendu syndrome. This genetic condition affects blood vessel formation throughout the body, including the brain.
In normal brain circulation:
- Arteries carry oxygen-rich blood to the brain
- Blood flows through progressively smaller vessels
- Capillaries slowly release oxygen to brain tissue
- Veins collect oxygen-depleted blood and return it to the heart
How AVMs Disrupt Normal Blood Flow:
- AVMs lack the normal network of small vessels and capillaries
- Blood rushes directly from arteries to veins without slowing down
- Brain tissue surrounding the AVM doesn’t receive proper oxygen
This abnormal blood flow pattern creates a high-pressure system that can lead to various complications. The vessels in an AVM may be fragile and prone to rupture, which explains why bleeding is a common problem with these malformations.
Risk Factors
Some people have a higher chance of having a brain arteriovenous malformation (AVM). These risk factors include:
Gender: Men are more likely to develop brain AVMs than women.
Family History: In rare cases, brain AVMs may run in families. While a specific genetic link hasn’t been clearly identified, some people inherit medical conditions that increase their AVM risk, such as hereditary hemorrhagic telangiectasia (HHT).
Complications
Brain arteriovenous malformations (AVMs) can lead to several serious health issues if left untreated. These abnormal connections between arteries and veins can cause problems throughout the brain.
Brain Bleeding
One of the most dangerous complications is bleeding in the brain. The walls of blood vessels within an AVM become thin and weak due to high pressure.
This weakness can cause the AVM to rupture, leading to bleeding in the brain tissue.
The yearly risk of bleeding ranges from 2% to 3%, though certain AVM types carry higher risks. People who have experienced previous bleeding may face increased chances of another episode.
Brain AVMs cause about 2% of all hemorrhagic strokes annually. They are particularly common causes of brain bleeding in children and young adults.
Oxygen Deprivation
Normal brain blood flow follows a path from arteries through tiny vessels called capillaries before reaching veins. In an AVM, blood bypasses these capillaries and flows directly from arteries to veins at high speed.
This abnormal flow pattern prevents surrounding brain tissue from absorbing enough oxygen. The resulting oxygen deprivation can lead to:
- Difficulty speaking
- Weakness on one side of the body
- Numbness
- Vision problems
- Balance difficulties
Aneurysm Formation
The extreme pressure within an AVM can cause bulges to form in vessel walls, called aneurysms. These balloon-like structures have a high risk of rupturing, which would cause additional bleeding.
Brain Compression
As the body tries to supply more blood to the fast-flowing AVM, the malformation may grow larger. This growth can:
- Displace normal brain tissue
- Compress important brain structures
- Block the flow of protective fluid around the brain
- Cause fluid buildup that pushes brain tissue against the skull
Vein of Galen Malformations
A specific type of AVM affects the vein of Galen. This condition presents serious complications in infants. These complications appear at birth or shortly after.
The symptoms of this AVM include:
- Fluid buildup in the brain
- A swollen head
- Visible enlarged veins on the scalp
- Seizures
- Failure to thrive
- Heart failure due to the cardiovascular strain
Early diagnosis and treatment of brain AVMs is essential. This is to prevent these serious complications from developing or worsening over time.
