What is Arteriovenous Malformation of the Brain?
Arteriovenous malformations (AVMs) are a kind of birth defect that affects your blood vessels. They involve a jumbled bunch of poorly developed blood vessels where the arteries (which carry blood from the heart) are directly linked to veins (which carry blood back to the heart) with no tiny vessels called capillaries in between.
These anomalies can appear anywhere in your body, but when they form in the brain it’s a big concern. That’s because these abnormal blood vessels in the brain have a high chance of bleeding, which can lead to a damage to the nervous system.
What Causes Arteriovenous Malformation of the Brain?
We don’t fully understand what causes brain AVMs (abnormal connections between arteries and veins in the brain). The reason is likely a combination of many factors. It might be due to genetic changes and a process called angiogenesis, where new blood vessels form from existing ones, both playing a part in the development of AVMs.
Some experts think that AVMs might start forming before a person is even born. Others suggest these abnormalities might occur after a person has a certain kind of stroke, either due to lack of blood flow to the brain or bleeding in the brain.
Risk Factors and Frequency for Arteriovenous Malformation of the Brain
The rate of occurrence of arteriovenous malformations (AVMs) in the United States is 1.34 for every 100,000 people each year. However, the actual number of these conditions may be higher because not all AVMs show symptoms. Only an estimated 12% of AVMs actually cause symptoms. Among patients who experience a hemorrhage (bleeding), 10-15% of them might not survive. Additionally, between 30-50% of these patients may suffer from health-related issues or complications. AVMs affect males and females equally. Even though these malformations are believed to be present from birth, the symptoms usually start to show in young adulthood.
- The occurrence of AVMs in the United States is 1.34 per 100,000 people each year. However, the actual count may be higher.
- About 12% of AVMs cause symptoms.
- 10-15% of patients may not survive if a hemorrhage occurs, while 30-50% may experience health problems as a result of the condition.
- Both males and females are equally affected by AVMs.
- Despite being present from birth, symptoms usually show up in young adulthood.
Signs and Symptoms of Arteriovenous Malformation of the Brain
Arteriovenous malformations (AVMs) are usually silent, with about 15% of cases not showing any symptoms until an event occurs. These events can be serious and include things like bleeding in the brain.
Between 41 and 79 percent of AVMs are noticed when they cause bleeding within the skull, known as intracranial hemorrhage. In fact, AVMs are the second leading cause of these types of bleeds after cerebral aneurysms. AVMs are responsible for 10% of subarachnoid hemorrhages, which happen in the space between the brain and the tissue that covers it. Children are more likely to have this bleeding symptom than adults.
Bleeding symptoms can range from loss of consciousness and severe headache to nausea and vomiting when the clotted blood starts breaking down in the spinal fluid. The bleed can also damage brain tissue and cause problems like:
- Seizures
- Weakness on one side of the body (hemiparesis)
- Loss of touch sensation on one side
- Difficulty understanding or producing language
Some AVMs can cause a little bleeding that may not cause any noticeable symptoms. After the bleeding stops, most people tend to recover as the blood vessels repair themselves.
AVMs can also cause seizures in 15 to 40% of patients. This risk goes up if the AVMs are located in the cortex, are large, multiple, or drain towards the surface of the brain. These seizures usually start in one section of the brain, but they can spread to other parts.
Progressive neurological deficit or a gradual worsening of brain function happens in 6 to 12% of patients over several months to years. This could be due to a “vascular steal syndrome”. But, most of the time, it’s related to the mass effect, bleeding, or seizures. Symptoms can include:
- Seizures
- Weakness on one side of the body
- Visual disturbances
- Loss of sensation on one side of the body
- Difficulty understanding or producing language (aphasia)
Another symptom of AVM could be a headache. However, headaches associated with AVM don’t have any specific characteristics. So, they could be just by chance and not because of the AVM.
Testing for Arteriovenous Malformation of the Brain
Brain AVM, which are abnormalities in blood vessels, are usually first spotted through two types of imaging techniques: a CT scan or an MRI. Combining MRI and angiography can be beneficial to plan the treatment and estimate the success rate and associated risks of surgery or other therapies.
In a CT scan without contrast, the abnormal vessel area stands out because its blood density makes it slightly more visible than the surrounding tissues. Large vessels and calcifications may also be noticeable. Despite this, no significant swelling or fluid accumulation is usually seen unless there’s bleeding. After taking a CT scan with contrast, especially with a CT angiogram, the diagnosis is straightforward as the feeding arteries, abnormal vessels, and draining veins can be easily seen. This appearance has often been described as a “bag of worms”. The detailed structure of these vessels can typically be identified using angiography. However, the sensitivity of CT scans to identify brain AVMs during a hemorrhage can be low due to compression of the abnormal vessels, thus, more sensitive techniques like MRI or angiography might be needed.
MRI stands out for its high sensitivity in mapping the location of the problematic vessel area, along with any associated draining veins or distant bleeding events. The high-speed flow of blood in a cluster of tangled vessels generates snake-like and tube-like voids that can be observed in both T1 and T2 weighted images, and are particularly noticeable on T2 images. MRI can also help identify complications such as prior hemorrhages, surrounding brain swelling, and atrophy.
After radiosurgery, an MRI can evaluate the shrinkage of the abnormal vessel area, post-therapy swelling, as well as radiation necrosis in the radiated area.
Lastly, angiography remains the gold standard for diagnosis and treatment planning. It precisely evaluates the configuration of the abnormal vessel area, its relationship, and drainage to surrounding vessels. The presence of an associated aneurysm signifies a higher risk for hemorrhage. The contrast transit time, which is related to the flow state of the lesion, can provide critical information for planning endovascular treatments.
Treatment Options for Arteriovenous Malformation of the Brain
Treatment approaches for arteriovenous malformation (AVM) differ depending on a patient’s age and risk profile. Younger patients with one or more high-risk factors for AVM rupture should usually undergo invasive management. In contrast, older patients without these risk factors might only need medical management. This can involve controlling seizures with anticonvulsants and managing headaches with appropriate pain relief. Some important factors to consider when evaluating the risk of AVM rupture include whether the AVM has previously ruptured, the patient’s age, location of the AVM, size of the AVM, presence of aneurysms, and other characteristics related to blood vessels. Surgical intervention may also be required for patients with AVMs that cause uncontrollable seizures.
For patients likely to experience hemorrhage, a type of surgery called open microsurgical excision is often the primary treatment and can provide a cure. The Spetzler-Martin Grade (SMG) scale is commonly used to evaluate the risk of complications and the likelihood of dying during surgery for brain AVMs. The SMG scale gives points based on the AVM’s size, location, and manner of venous drainage, with higher points indicating a higher risk.
In cases where surgery carries a high risk for patients, alternatives like radiotherapy and endovascular embolization could be employed. These methods can also be used alongside surgery to improve outcomes.
What else can Arteriovenous Malformation of the Brain be?
When a doctor is trying to diagnose cerebral AVMs, or abnormal connections between the arteries and veins in the brain, there are many other medical conditions they must consider. These conditions might show similar symptoms but require different treatment approaches, so it’s essential for doctors to make the right diagnosis. These conditions include:
- Carotid/vertebral artery dissection, where there’s a tear in the artery of the neck or brain
- Cavernous sinus syndromes and thrombosis, referring to problems in the large vein at the base of the skull
- Cerebral amyloid angiopathy, which involves protein build-up in brain’s arteries
- Cerebral venous thrombosis, a blood clot in the brain’s veins
- Dissection syndromes, a term for conditions involving tears in blood vessels
- Fibromuscular dysplasia, a condition that causes irregular growth in artery walls
- Intracranial aneurysms, the bulging in brain’s blood vessels
- Migraine and cluster headaches, types of severe, recurring headaches
- Moyamoya disease, a rare blood disease involving brain’s arteries
- Stroke, wherein blood supply to the brain stops
- Vein of Galen malformation, a rare blood vessel abnormality inside the brain
Doctors must run appropriate tests and use careful judgment to determine whether these conditions might be causing the patient’s symptoms instead of, or in addition to, cerebral AVMs.
What to expect with Arteriovenous Malformation of the Brain
There are several scoring systems designed to assess the risk and potential complications related to different treatments for brain vascular malformations, also known as cerebral Arteriovenous Malformations (AVMs). These systems help to understand whether to monitor the AVM or to intervene through treatment. Here are the main ones:
1. The Spetzler-Martin scale: Used primarily for assessing the risk associated with a type of surgery called microsurgery.
2. The Supplementary Spetzler-Martin scale: An additional scale often used in conjunction with the first when evaluating risk in microsurgery.
3. The Pittsburgh radiosurgery-based AVM grading scale: This is used to evaluate the risks related to radiosurgery, which is a form of radiation therapy.
4. The Toronto score: Similarly to the Spetzler-Martin scale, the Toronto score is also used primarily for risk assessment in microsurgery.
5. The Buffalo Score: This system is typically used for assessing risks associated with endovascular treatment, which is a minimally invasive procedure often used for treating AVMs.
Possible Complications When Diagnosed with Arteriovenous Malformation of the Brain
The main problems that can occur with AVMs (arteriovenous malformations) are:
- Bleeding in the brain
- Pressure effects from the mass
- Seizures
- Steal phenomenon (where normal blood flow is disrupted)
- Neurological issues or loss of function
Preventing Arteriovenous Malformation of the Brain
If a patient is being treated conservatively for a brain lesion, it’s essential to inform them about the risk of experiencing internal brain bleeding and seizures. In addition, it’s necessary to evaluate and confirm their ability to drive safely.
