What Is An Arteriovenous Malformation
A brain Arteriovenous Malformation (AVM) is an abnormal connection between arteries and veins that interrupts the normal flow of blood between them. An AVM, which is present at birth (congenital), can develop anywhere in your body but occurs most often in the brain or spine. A brain AVM, which appears as tangles of normal and dilated blood vessels, can occur in any part of your brain. The cause isn’t clear. Doctors believe that a brain AVM develops during fetal development. Why this occurs for some babies and not others is unknown.You may not know you have a brain AVM until you experience symptoms, such as headaches or a seizure. In serious cases, the blood vessels rupture, causing bleeding in the brain (hemorrhage). Once diagnosed, a brain AVM can often be treated successfully.
Normally, your heart sends oxygen-rich blood to your brain through arteries, which branch into smaller arterioles and subsequently to capillaries, the smallest blood vessels. Oxygen is removed from blood in the capillaries and used by your brain. The oxygen-depleted blood then passes into small venules and then into larger veins that drain the blood from your brain, returning it to your heart and lungs to get more oxygen. If you have a brain AVM, blood passes directly from your arteries to your veins via abnormal vessels. This disrupts the normal process of how blood circulates through your brain.
A brain AVM (arteriovenous malformation) often causes no signs or symptoms until the AVM ruptures, resulting in bleeding in the brain (hemorrhage).
Signs and symptoms of a brain AVM include:
- Seizures
- A whooshing sound (bruit) that can be heard on examination of the skull with a stethoscope
- Pulsing noise in the head (pulsatile tinnitus)
- Headache
- Progressive weakness or numbness
When bleeding into the brain occurs, signs and symptoms can be similar to a stroke and may include:
- Sudden, severe headache
- Weakness or numbness
- Vision loss
- Difficulty speaking
- Inability to understand others
- Severe unsteadiness
A bleeding brain AVM is life-threatening and requires emergency medical attention.
Symptoms may begin at any age, but you’re more likely to experience symptoms before age 50. Brain AVM can damage brain tissue over time. The effects slowly build up, sometimes causing symptoms in early adulthood. Once you reach middle age, however, brain AVMs tend to remain stable and are less likely to cause symptoms.
For women, pregnancy may start or worsen symptoms because of the increased blood flow and blood volume during pregnancy.
Treatment options for brain AVM involve a number of procedures and depend on the size and location of the abnormal blood vessels. Medications may also be used to treat related symptoms, such as headaches or seizures.
Surgical removal (resection)
ASurgical treatment of a small brain AVM is relatively safe and effective. A section of skull is removed temporarily to gain access to the AVM. The neurosurgeon, aided by a high-powered microscope, seals off the AVM with special clips and carefully removes it from surrounding brain tissue. Sometimes this is done with a laser. The skull bone is then reattached, and the scalp is closed with stitches.
Resection is usually done when the AVM can be removed with acceptable risk to prevent hemorrhage or seizures. AVMs that are in deep brain regions carry a higher risk of complications. In these cases, other treatments are considered.
Endovascular embolization
During this procedure, a long, thin tube called a catheter is inserted into a leg artery and threaded through the body to the brain arteries. The catheter is positioned in one of the feeding arteries to the AVM, and small particles of a glue-like substance are injected to block the vessel and reduce blood flow into the AVM.
Endovascular embolization may be done alone, before other treatments to reduce the size of the AVM, or during surgery to reduce the chance of bleeding during the operation. In some large brain AVMs, endovascular embolization may reduce stroke-like symptoms by redirecting blood back to normal brain tissue.
Stereotactic radiosurgery
This treatment uses precisely focused radiation to destroy the AVM. The radiation causes the AVM vessels to slowly clot off in the months or years following the treatment. This treatment works best for small AVMs and for those that have not caused a life-threatening hemorrhage.