Arteriovenous Malformation (AVM)
An arteriovenous malformation (AVM) is a tangle of abnormal blood vessels connecting arteries and veins. They can develop anywhere in the body but are most common in the brain
What Are the Causes of AVM?
The exact causes of an AVM are not known. In most cases patients are born with the AVM but occasionally they can develop later in life.
AVMs are more common in males and in patients with a family history of AVMs. However it is unclear if there is a genetic link or if the cases within a family are coincidental. AVMs can also occur in patients with rare diseases of the blood vessels.
What Are the Symptoms of AVM?
In many cases an AVM causes no symptoms and is found by accident when a scan of the brain is performed for other reasons. In some cases an AVM in the brain may cause headaches and/or seizures (fits). If an AVM ruptures (bursts) it can cause bleeding (haemorrhage), which can cause severe headaches and symptoms similar to a stroke, such as muscle weakness or numbness, loss of vision, difficulty speaking, or confusion.
If an AVM results in bleeding, death can occur in 10-15% of cases.
Symptoms from an AVM may start at any age, but most commonly occur between 10 and 40 years of age. After middle age AVMs tend to remain stable and are less likely to cause symptoms.
Symptoms may increase during pregnancy due to changes in blood volume and blood pressure.
What Are the Treatment Options?
The aim of treating an AVM is to reduce the risk of bursting and bleeding. Not all AVMs will bleed, but the estimated risk of this is 2-4% per year. There are several treatment options available depending on the age of the patient, the size and location of the AVM, and whether there has been previous bleeding. These factors are weighed up against the risks of the particular treatment.
Surgical Removal is the most common treatment and is most effective when the AVM is smaller and easily accessible for the surgeon. During surgery the AVM is located and sealed off with special clips before it is removed from the surrounding brain tissue.
If the AVM is located in a deep region of the brain or if the risk of complications from surgery is high, other treatment options are preferred
Stereotactic Radiation Therapy/Radiosurgery uses multiple precisely focused x-ray beams to destroy the AVM. It is a non-surgical and non-invasive treatment.
A plastic ‘mask’ or head frame is worn during the treatment to keep the patient’s head still.
Stereotactic radiosurgery is usually delivered in a single session of treatment. Stereotactic radiation therapy is delivered over a number of sessions on different days.
During the treatment multiple highly targeted x-ray beams are focused on the AVM. This causes changes in the blood vessel walls and eventually scarring. The scarred AVM blood vessels then slowly clot off in the 1-3 years following treatment. During the time it takes for the blood vessels to close there is still a risk of bleeding from the AVM. Patients are closely followed up during this time.
Endovascular Embolisation In this procedure a catheter is inserted into an artery in the groin and using X-ray guidance, the catheter is threaded through the blood vessels into the brain. The catheter is then positioned in one of the arteries that feeds into the AVM. The artery is blocked by the insertion of a glue-like substance or coil and blood no longer flows through the AVM.
Embolisation is less invasive than conventional brain surgery, and may be used when the risks associated with surgery are high. It can also be used prior to conventional surgery or radiation therapy to reduce the size of the AVM and the risk of bleeding.
How effective is radiation therapy for AVM?The success of destroying AVMs with radiation therapy depends on the size of the AVM, and the radiation dose given.
Smaller AVMs have the highest chance of success treatment with radiation therapy. Overall, the rate of success at 3 years is approximately 80% for AVMs that are 3cm or smaller.
For larger ones, the success rate seen in studies is variable, between 30 to 70%.
What are the side effects of radiation therapy?
Side effects during/soon after treatment (Early or ‘acute’ side effects)
Most patients will not notice any side effects during stereotactic radiation therapy, although headaches or nausea are possible.
Side effects well after treatment (Late or long-term side effects)
Late side effects may occur a few months to years after treatment. Depending on the problem it may occur once and then go or may be more persistent over the long term or may come and go over time. The likelihood of developing late side effects from radiation treatment depends on the amount of radiation and how close the AVM is to important structures located nearby. Your Radiation Oncologist will explain the potential late side effects of your treatment and how to manage potential side effects in more detail.
One possible long term side effect includes damage to surrounding brain tissue (necrosis). Necrosis can cause new neurological symptoms, fits, or headaches. These types of side effects generally take many months to years to develop. Overall the risk of radiation necrosis causing permanent neurologic problems is reported to be between 1-3%.
The best person to discuss radiation therapy with is a Radiation Oncologist. You can ask your surgeon or General Practitioner for a referral to a Radiation Oncologist for a discussion whether radiation therapy is a suitable treatment option for you.
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