Table of contents:
- Normal arterial and venous connection
- Abnormal artery and vein connection
- What does a brain AVM look like?
- Who could potentially experience a brain AVM?
- What are the symptoms of an AVM?
- How do I diagnose an AVM?
- How do I handle AVM?
- What about the prognosis?
An artery malformation, or AVM for short, is a group of abnormal blood vessels that are interconnected with one another. AVMs can occur in different parts of the body, but brain AVMs are the most problematic. Another term for AVM is arteriovenous fistula.
In order to understand the reasons why AVMs are dangerous, it is first important to understand how normal blood vessels relate to one another.
Normal arterial and venous connection
There are two main types of blood vessels: arteries and veins. Arteries carry oxygen-rich blood from the heart and lungs to other parts such as muscles, bones and brain, while veins carry blood back to the heart and lungs to get oxygen again. As the arteries move deeper into the tissues of the body, they become smaller and smaller, until they reach a point of maximum narrowing - these are known as capillaries. Blood flow slows down so that it can be transferred from the arteries to the veins.
Thus, one of the important functions of the capillaries is to relieve some of the pressure that is concentrated on the blood as it flows through the larger arteries into the tissues.
Veins exit the capillaries and progressively enlarge as they leave the organs on their way back to the heart and lungs to add oxygen.
Abnormal artery and vein connection
Brain AVMs originate from connected arteries and veins in the absence of capillaries. This causes pressure on the arteries as it travels directly to the veins within reach of the AVM. This rare blood flow produces a region that has high pressure and turbulence and causes the AVM to enlarge over time, affecting the function of surrounding brain tissue.
What does a brain AVM look like?
Brain AVMs vary in shape. Some are usually small and cannot be seen for decades. Others form large, tortuous ducts in the arteries, which pulsate strongly as they connect directly to the vein. AVMs can be found anywhere in the brain, including the brain cortex, white matter, and the brain stem.
Who could potentially experience a brain AVM?
Brain AVMs affect about 0.1% of the population, some even begin at birth, but rarely affect more than one member of the same family. They occur equally in men and women. People generally start feeling symptoms between the ages of 10 and 30, but it's rare for those over 50.
What are the symptoms of an AVM?
About half of patients recognize AVMs after experiencing subarachnoid hemorrhage. The other half are affected because of convulsions, headaches, and stroke symptoms such as hemiplegia or hemiparesis.
How do I diagnose an AVM?
The diagnosis of AVM is often made by radiologists with just a CAT scan of the brain. However, most doctors feel more comfortable making an AVM diagnosis after performing an MRI examination. In cases when bleeding occurs, the AVM can be completely obscured by intracerebral hemorrhage, requiring a cerebral angiogram to determine the final diagnosis.
How do I handle AVM?
The most common types of treatment available include surgical resection, endovascular embolization, and stereotactic radiosurgery, all of which can be used either alone or in combination. In general, this treatment aims to reduce the risk of bleeding, and prevent re-bleeding.
An issue currently under intensive research is whether doctors should treat AVMs before they cause bleeding. As it turns out, no studies have assessed the risk of bleeding when the AVM ruptures and sometimes the AVM symptoms are not treated. Some people even believe that AVMs found before bleeding have a lower risk than those found after bleeding. Nonetheless, the uncertainty causes many surgeons and patients to decide on surgery, despite the risk that the procedure itself could lead to permanent brain injury.
What about the prognosis?
The prognosis of an AVM depends on several factors, starting with whether the AVM was found before or after bleeding. More than 90% of those who experience bleeding can be saved after the incident. In those whose AVM is found before bleeding, the prognosis is directly related to AVM size, symptoms, proximity to vital brain areas and, as noted above, whether or not the AVM is being treated.
