An arteriovenous malformation (AVM) is a congenital disorder (present from birth) characterized by a complex, tangled web of arteries and veins in which there is a short circuit and high pressure due to arterial blood flowing rapidly in the veins. An AVM may occur in the brain, brainstem or spinal cord. The most common symptoms of an AVM include hemorrhaging (bleeding), seizures, headaches and neurological problems such as paralysis or loss of speech, memory or vision. AVMs that bleed can lead to serious neurological problems and sometimes death. Both localized and diffuse lesions are seen in internal organs such as the brain, lung, liver and intestines. Lesions within the brain are the most common arteriovenous malformation. They are initially silent, with symptoms depending upon the rapidity of enlargement. Still, some people have AVMs that never cause problems.
It’s not clear why AVMs form, but researchers believe that these tangles of vessels are present from birth. Several rare genetic diseases are associated with AVMs. They are generally thought to be caused by errors in the formation and development of the normal arterial-capillary-venous connections that occur very early in prenatal development. Some arteriovenous malformations can be associated with syndromes due to genetic abnormalities. RASA1 mutations and hereditary hemorrhagic telangiectasia (HHT) have been associated in some cases of brain AVMs. HHT also increases risk of lung and liver AVMs. PTEN mutations have been found in association with diffuse AVMs, particularly in combination with fatty overgrowth or mass.
There is no evidence that drugs or medications taken during pregnancy or environmental exposures during that time cause AVMs.
The size, shape and location of brain AVMs can be detected using imaging tests such as:
- MRI (magnetic resonance imaging)
- CT (computed tomography)
- Cerebral Angiogram MRA (magnetic resonance angiography)
- CTA (computed tomography angiography)
Many AVMs are discovered only after they bleed or cause symptoms, because people with AVMs often have no symptoms. Like unruptured aneurysms, many AVMs can be detected incidentally during imaging for traumatic head injury, vision problems or headaches.
Complications can include ulceration of overlying skin, bleeding and persistent pain. If the blood flow through an arteriovenous malformation is excessive, the heart will enlarge over time due to the extra work of pushing blood through the AVM, and this may result in heart failure.
A few common AVM locations are:
Lungs – There is always a risk for rupture (bleeding) when there is AVM involvement in the lung, however the highest risk occurs during pregnancy as blood pressure and volume are likely to increase. When AVMs are present in lungs, there is also a risk for stroke or brain abscess due to the lack of capillary filtering of impurities such as clots, air bubbles and bacteria.
Brain – Brain AVMs can bleed, causing neurologic compromise. Signs may include dizziness, headache, or visual changes.
Liver – Most individuals with liver AVMs are not treated because they rarely bleed or cause any other sudden medical complications. Later in life, liver or heart failure can sometimes occur.
Treating AVM as soon as possible is the best way to avoid serious complications. AVMs sometimes require a combination of treatments, including surgery, embolization and radiation.
- Surgery: Surgical resection is performed to remove the tangled blood vessels. The surgeon uses a procedure called a craniotomy to reach the brain, during which a small opening is created in the skull. Once the surgeon has access to the AVM, the abnormal arteries and veins are removed. This redirects blood flow to normal vessels, preventing the AVM from leaking or bursting.
- Embolization: Embolization involves inserting a type of glue into the AVM through a very thin tube called a catheter. This blocks blood flow into the AVM, which may help limit blood loss during surgery, as well as slow blood flow which may reduce the chance of bleeding if open surgery is not performed immediately afterwards.
- Radiosurgery: During radiation treatment, beams of highly energized photons (light particles) are directed at the AVM using a tool called a Gamma Knife. Over time, this causes the AVM to shrink and scar, closing down abnormal blood vessels, so that blood no longer flows through them, reducing the risk of bleeding, and also perhaps making the AVM easier to treat using open surgical techniques.
Arteriovenous Malformation (AVM). (n.d.). Retrieved March 16, 2017, from https://my.clevelandclinic.org/health/articles/arteriovenous-malformations
Arteriovenous Malformations. (n.d.). Retrieved March 16, 2017, from https://www.cincinnatichildrens.org/health/a/arteriovenous