What is Arteriovenous Malformations of the Central Nervous System?
An arteriovenous malformation (AVM) is an unusual link between arteries and veins that bypasses tiny blood vessels called capillaries. The absence of capillaries causes the veins to carry blood that’s directly from the arteries, creating a high-flow, low-resistance system. Cerebral or brain AVMs can lead to an annual 1% risk of epilepsy and a 3% risk of bleeding. This includes a 2% annual risk of bleeding for unruptured AVMs and a 4.5% annual risk for previously ruptured AVMs.
These brain AVMs can differ greatly in size, location, and how blood flows through them. They are most often found within the cerebral cortex (the outermost layer of the brain), the brainstem, and the cerebellum. In addition, AVMs can also occur within the spinal cord. The Spetzler-Martin grading scale is commonly used to classify these brain AVMs based on their complexity. As the grade on this scale goes up, the risks from surgery to treat the AVM also go up.
Spinal AVMs can be categorized as either being inside the spinal cord (intramedullary), outside it (perimedullary), or both. They can be either direct connections between an artery and a vein or connections through a group of tiny non-capillary vessels, also referred to as true nidal fistulas. There are four types of spinal AVMs, according to the Kim-Spetzler system. Recent classification includes a fifth type found within the conus medullaris, the lower end of the spinal cord.
Direct connections represent about 20% of spinal AVMs and are usually located on the spinal cord’s surface. True nidal spinal AVMs make up 80% of cases; they are typically inside the spinal cord. Children are more likely to have direct connection AVMs, while adults more often have true nidal spinal AVMs. Often spinal AVMs can lead to persistent worsening of neurological function or bleeding that causes sudden back pain, leg pain, numbness, weakness, or issues with bowel or bladder control. About half of all spinal AVMs are found within the chest region of the spine, while another 30% are within the neck region.
What Causes Arteriovenous Malformations of the Central Nervous System?
Arteriovenous malformations (AVMs) are caused by abnormalities in blood vessel development even before birth. Although the exact process isn’t fully understood yet, it’s believed that these happen due to disruptions in the formation of blood vessels during the early stages of embryo development.
Around 5% of AVMs are found in people with inherited conditions such as Osler-Weber-Rendu syndrome, which is passed down through families. There’s also another related condition, which causes multiple small AVMs in the arms and face.
There have been several genetic changes observed in patients with sporadic AVMs, like changes in KRAS, a gene associated with numerous cancers, changes in SMAD9 and SMAD4, and variations in Notch-3 receptor expression. These changes can lead to several consequences, like increased signaling and factors that encourage the formation of blood vessels.
Other research has found substantial differences between the blood vessels in AVMs and those in healthy brain tissues, like changes in certain proteins called receptors, and heightened activity in over 700 genes involved in processes like inflammation and cell signaling.
Spinal AVMs, which are AVMs located in the spinal canal, are relatively rare, and account for only a tiny fraction of all lesions found within the spinal canal, or vascular malformations in the nervous system. People with Osler-Weber-Rendu syndrome are more prone to developing spinal AVMs. There are several other genetic syndromes, like Klippel-Trenaunay syndrome, Parkes-Weber Syndrome, and the spinal arteriovenous metameric Cobb Syndrome, that also increase the chance of developing spinal AVMs.
Risk Factors and Frequency for Arteriovenous Malformations of the Central Nervous System
Intracranial AVMs are conditions of the brain that often don’t show any symptoms, with about 88% of them being asymptomatic. When symptoms do show, in around 45% of cases, it’s often through a hemorrhage. The risk of hemorrhage for those with unruptured cerebral AVMs is about 2.2% every year, based on the findings of the A Randomized Trial of Unruptured Brain AVMs. The likelihood of having an AVM is significantly less than having other cerebral vascular malformations, like aneurysms, with a rate of about 1.12 to 1.34 per 100,000 people.
AVMs can affect anyone, regardless of sex, and usually becomes evident around the age of 33.7 years old. Among those who do present symptoms, around 36% to 38% have their first symptom as a hemorrhage. Even children can have intracranial AVMs, with an extremely low incidence of 0.02%, and no sex predisposition. Spinal AVMs, on the other hand, occur less frequently but are more common in boys when compared to cerebral AVMs. They typically present symptoms in individuals in their third decade of life, but can even affect children, who make up 20% of cases.
- Up to 88% of intracranial AVMs don’t show any symptoms.
- About 45% of symptomatic AVMs present through a hemorrhage.
- Unruptured cerebral AVMs have a 2.2% annual risk of causing a hemorrhage.
- The likelihood of having an AVM is around 1.12 to 1.34 per 100,000 people, which is significantly less than for other cerebral vascular malformations like aneurysms.
- There is no strong sex bias for getting an AVM, and symptoms typically first show up around the age of 33.7 years old.
- About 36% to 38% of people with symptoms have their first symptom as a hemorrhage.
- Intracranial AVMs also occur in children, with a very low rate of 0.02%, and without much sex bias.
- Spinal AVMs are less common than cerebral AVMs but are more likely to occur in boys, and typically affect people in their thirties, but can also be seen in children.
Signs and Symptoms of Arteriovenous Malformations of the Central Nervous System
Intracranial hemorrhage, or bleeding in the brain, can be caused by several conditions including chronic high blood pressure, a disease called amyloid angiopathy, abnormalities in the blood vessels (vascular malformations), or injury to the head. These abnormal blood vessels, which include aneurysms and arteriovenous malformations (AVMs), are often seen in individuals who have not suffered trauma, are between their twenties and sixties, smoke heavily, or have a family history of similar blood vessel abnormalities.
The symptoms a patient with an AVM experiences largely depends on where the AVM is located in the brain or spine, and whether it has caused bleeding. In adults, AVMs in the brain usually cause bleeding, which can lead to several possible symptoms such as weakness, changes in sensation, nerve-related issues in the face, seizures, or changes in consciousness. Particularly in people in their thirties and forties, AVMs account for a third of brain bleeds; seizures are the second most common symptom. Symptoms might be more frequently seen with AVMs in the temporal lobes (sides) of the brain. Other less frequent symptoms include focal neurologic deficits from mass effect, headaches, and vascular steal phenomena.
- Weakeness
- Sensory changes
- Facial nerve problems
- Seizures
- Altered consciousness
Patients with AVMs in the spine may experience two different sets of symptoms. In the case of a sudden bleed, they may feel sudden severe back pain, along with weakness in the legs, numbness or tingling, and problems with bladder or bowel control. An AVM in the spine that hasn’t bled might cause chronic low back pain or neurologic issues in the legs due to gradual pressure on the spinal cord. There’s also a specific condition called Foix-Alajouanine syndrome that presents with sudden or gradual myelopathy – injury to the spinal cord – due to a clot forming in the veins of the spinal cord, causing injury and death of spinal cord tissues.
Testing for Arteriovenous Malformations of the Central Nervous System
If you’re dealing with headaches or neurological problems, imaging tests are a key part to diagnosing brain and spinal blood vessel malformations, also known as AVMs. A non-contrast CT scan of your head is usually the first step. This scan can spot issues like fresh internal bleeding, blood-filled areas in the brain’s surface or chambers, or rule out dangers like a stroke, tissue growths, masses, or other non-bleeding related conditions. But in some cases, an AVM may not be easy to notice on a non-contrast head CT.
A CT angiogram, which provides a detailed view of your blood vessels, can be very helpful. This method can offer critical insights about the structure of the AVM, critical arteries fueling it, potential aneurysms inside the AVM, and the deep veins that help in drainage. One study showed that a CT angiogram could catch 90% of brain AVMs, while magnetic resonance angiograms, or MRAs, only found 74%. The most reliable method for detecting blood vessel malformations is a digital subtraction angiogram, or DSA, which provides images with clearer detail and real-time view of the blood flow.
Magnetic Resonance Imaging (MRI) scans of the neck, chest, and lower back, taken with and without a contrast agent, are suggested as the first step to diagnose spinal AVMs. MRIs help rule out concerns like tissue growths, infections, spinal cord injuries, swelling from spinal disc problems, and fluid build-up outside the spinal cord. A contrast-enhanced MRA significantly enhances the clarity and can be an essential step before a DSA to evaluate blood-supplying vessels. But the most dependable method of examining spinal blood flow is a spinal DSA, because it gives a greatly detailed view of blood vessel structure and shows the timing of blood flow via supplying and draining vessels.
Besides imaging tests, you’ll also have to do some lab tests to check how your blood clots, kidney’s health before using contrast agents in imaging tests, and your overall fitness level before making treatment decisions. This includes a total blood count, full metabolic panel, tests to determine the time your blood takes to clot (INR, PT and PTT tests), and blood typing for potential blood transfusions.
Treatment Options for Arteriovenous Malformations of the Central Nervous System
The Spetzler-Martin AVM Grading System is a method used to evaluate the risk associated with surgical removal of blood vessel abnormalities in the brain and spine, known as arteriovenous malformations (AVMs). The system, developed in 1986, assesses the AVM based on size, blood flow (venous drainage), and the sensitivity or “eloquence” of the brain area it’s located in. Each of these factors is assigned a point value, which is summed up to give an overall grade ranging from I (least risky) to V (most risky). There’s also a special grade called VI for cases that are considered inoperable.
AVMs smaller than 3 cm, that only connect with superficial veins, and that are located in less delicate parts of the brain get the lowest point values. Those larger than 6 cm, draining into deep veins, or located near sensitive brain areas like the sensory or language cortex get higher point values.
When an AVM causes symptoms such as unmanageable seizures or worsening neurological problems, doctors often need to intervene urgently. Generally, surgical removal is the go-to option for AVMs that are superficial, while stereotactic radiosurgery (a type of radiation therapy) is used for those located deep in the brain.
However, the Spetzler-Martin grade of an AVM influences the treatment approach. Lower-graded AVMs (I and II) are typically handled with surgery, grade III with a procedure called endovascular embolization, and higher-graded AVMs (IV and V) with stereotactic radiosurgery. Endovascular embolization can also be done first to decrease the size of the AVM before carrying out stereotactic radiosurgery. Regardless of the approach, the goal is to completely disconnect the abnormal blood vessels that make up the AVM.
Some studies, such as the ARUBA trial, suggest that there might be less risk of stroke and death when patients are monitored closely but not treated aggressively compared to those who received proactive surgical or other interventions.
Similar methods apply for treating AVMs in the spine. The aim is to prevent or halt worsening neurological symptoms caused by the AVM. Spinal AVMs can rebleed at a rate of about 10% per year, sometimes prompting more urgent treatment. Depending on the situation, these spinal AVMs can be treated with surgery, embolization, or a combination of both. Improvement in neurological symptoms is possible after treatment, although some patients may still experience lingering symptoms.
What else can Arteriovenous Malformations of the Central Nervous System be?
Brain AVMs (arteriovenous malformations) can be diagnosed after showing symptoms like bleeding within the brain, pressure effects, or seizures. But they are often detected in people who don’t show any symptoms and are undergoing brain scans for unrelated reasons. If someone suddenly experiences a brain bleed, the potential causes could be a brain AVM, a burst aneurysm (ballooning blood vessel), a certain kind of blood vessel abnormality in the covering of the brain, a blood vessel disease related to aging, a bleeding tumor, a tiny stroke caused by hypertension, or an injury to the brain.
For people who have seizures, the list of possible causes gets longer. Conditions leading to brain swelling, like a brain AVM, a tumor, an abscess (pocket of pus), an inflammation of the brain coverings (meningitis), and a condition causing increased brain fluid can cause seizures. Additionally, certain brain abnormalities and inherited conditions causing seizures also need consideration.
In people showing signs of spinal AVM (back pain and sudden or worsening nerve-related issues), the potential reasons could be pressure effects due to spinal cord tumors, slipped disc, bone infection, spinal disc infection, fractures due to disease conditions, worn out spinal discs, sudden spinal injury, and blood vessel malformations. Most spinal AVM patients are diagnosed after experiencing a gradual worsening of nerve-related issues.
What to expect with Arteriovenous Malformations of the Central Nervous System
The future health outcomes associated with an intracranial AVM, or abnormal connection between arteries and veins in the brain, often depend on whether it has ruptured before. An unruptured AVM has an annual risk of rupture of 2.2%, while AVMs that have already ruptured face a 4% annual risk.
In 2019, a study introduced the R2eED AVM Score to assess the risk of bleeding. This score considers a variety of factors that could increase the risk, like the specific size and location of the AVM, a single supplying artery, and the deep vein system involved. Also, being of non-White ethnicity increases the risk.
The severity of brain damage and chances of recovery depend on the volume and location of the rupture.
Possible Complications When Diagnosed with Arteriovenous Malformations of the Central Nervous System
There’s ongoing debate around how to manage brain AVMs (arteriovenous malformations – abnormal connections between arteries and veins). The worry is about the risk of complications from surgery versus the risk of the AVM bursting, or bursting again. Problems linked to surgery can include strokes, brain bleeding, seizures, and even death. A study called the ARUBA trial looked at treating unruptured AVMs through surgery and compared it to simply monitoring them. The study found that the group treated with surgery had a significantly higher rate of death from any cause and strokes. Other complications of brain AVMs include the “vascular steal phenomenon”, where blood is redirected away from normal brain tissue, and “mass effect”, which is pressure on the brain caused by a growing lesion.
Complications of spinal AVMs (also abnormal connections between arteries and veins but located in the spine) include bursts that lead to bleeding and neurological problems due to a progressive mass effect.
Typical complications include:
- Stroke
- Brain bleeding
- Seizures
- Death
- Redirected blood flow away from normal brain tissue (vascular steal phenomenon)
- Pressure on the brain caused by a growing lesion (mass effect)
- Neurologic problems caused by bleeding and progressive mass effect in spinal AVMs
Preventing Arteriovenous Malformations of the Central Nervous System
Arteriovenous malformations, or AVMs, are unusual links between arteries and veins that are present from birth. They connect these blood vessels directly, without any normal tissue in between. People with AVMs often don’t show any symptoms until their 30s or 40s. Internal AVMs in the head can lead to seizures due to the mass effect or small blood leaks, weakness or numbness from the mass effect, or a serious rupture causing significant bleeding. The exact symptoms depend on the AVM’s location. The approach to treating these AVMs varies, depending on factors like their size, location, and whether deep veins are involved.
Often, AVMs that aren’t causing symptoms are discovered during head or back scans for other conditions, such as headaches or back pain. In these cases, the patient should consult with a specialist in brain surgery to discuss the risks and the chance of the AVM getting worse. Regular follow-ups involving brain exams and monitoring scans are highly recommended.
In most cases, AVMs occur randomly. However, if a person has certain inherited conditions, like hereditary hemorrhagic telangiectasia, it could raise the likelihood of having multiple AVMs. The treatment choices for AVMs in the head include regularly scheduled scans, targeted radiation therapy, using a substance to block the blood vessels (endovascular embolization), and traditional open surgery. For AVMs in the spine, similar treatments are used: regular scans, endovascular embolization, or open surgery.
