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Natural History and Treatment Options


A brain arteriovenous malformation (AVM) is a tangle of abnormal blood vessels connecting arteries (which carry blood under high pressure) and veins (which carry blood under low pressure) in the brain. These vessels have a higher rate of bleeding than normal blood vessels.

The cause of brain AVMs is not clear, but it is believed that most brain AVMs appear during fetal development. Occasionally, brain AVMs can form later in life, but they are rarely passed down among families genetically. A brain AVM is not a cancer and does not spread to other parts of the body.

AVMs are commonly found after a brain scan for another health reason or after the blood vessel rupture and cause bleeding in the brain. This happens in around 50% of the cases. Some people with brain AVMs have no symptoms (an unknown proportion of the population with brain AVMs). Some people may experience

  • Headache (presentation in ~16% of cases),

  • Seizures (presentation in ~25% of cases)

  • Stroke-like symptoms such as muscle weakness or numbness in one part of the body not associated with bleeding (presentation in ~8% of cases) or

  • A combination of these events.

Natural History 

The true natural history of brain AVMs is not clear as there is no study that is sufficiently large enough or had been carried out for long enough to truly observe the behaviour of brain AVMs. However, based on available published literature, it is reasonable to assume that the yearly risk of bleeding lies somewhere between 1.3% and 2.2%.

There are a number of factors that are known to increase the likelihood of bleeding. These include

  • Gradual narrowing of the draining veins (venous outflow stenosis) – from acquired “wear and tear” changes in the vein leading to progressive luminal narrowing (intimal hyperplasia) in the veins. This results in a backlog of blood and therefore greater pressure in the AVM bed and eventual rupture. 

  • Presence of a coincidental brain aneurysm

  • Older age

  • Pregnancy – there is an increased risk of bleeding from a brain AVM during pregnancy usually after the first 3 months of pregnancy, through to the post-partum period. It is thought that this is because there is an increase in the blood volume and changes in hormones to the mother during this period.

Treatment Options

Not all unruptured brain AVMs require treatment. Treatment recommendation needs to take into consideration the risk versus benefit of repairing the newly discovered AVM. These factors include patient’s age and life expectancy, any co-existing medical conditions that may complicate treatment, the AVM architecture and where it is located, and the treating surgeon’s skill set and track record in repairing brain AVMs.

In general, brain AVMs may be 1) observed closely with regular scans, 2) undergo radiotherapy treatment, 3) blocked off using glue by endovascular treatment, 4) surgery to remove the AVM, or a combination of these treatments.

When feasible, surgery offers the best chance of achieving a cure as most AVM do not grow back once completely removed. This eliminates the future bleeding risk from the AVM. An individual assessment balancing the risk of spontaneous AVM bleeding against that of available treatment options requires expert evaluation and discussion.

Some useful references 

  1. Gross B, Du R:  Natural history of cerebral arteriovenous malformations: a meta-analysis.  J Neurosurg. 2013; 118(2):437-443.

  2. Kim H, Al-Shahi Salman R, McCulloch CE, Stapf C, Young WL, MARS Coinvestigators. Untreated brain arteriovenous malformation.  Patient-level meta-analysis of hemorrhage predictors. Neurology. 2014;83(7):590-597

  3. Hernesniemi J, Dashti R, Juvela S, Vaart K, Niemela M, Laakso A. Natural history of brain arteriovenous malformations: A long-term follow-up study of risk of hemorrhage in 238 patients. Neurosurgery. 2008;63(5):823-831

  4. Al-Shahi Salman R, White PM, Counsell CE, du Plessis J, van Beijnum J, Josephson CB, Wilkinson T, Wedderburn CJ, Chandy Z, St George J, Sellar RJ, Warlow CP; for the Scottish Audit of Intracranial Vascular Malformations Collaborators. Outcome after conservative management or intervention for unruptured brain arteriovenous malformations. JAMA. 2014;311(16):1661-1669

  5. Spetzler RF, Ponce FA. A 3-tier classification of cerebral arteriovenous malformations.  J Neurosurg. 2011; 114:842-849

  6. Patel NJ, Bervini D, Eftekhar B, et al: Results of surgery for low-grade brain arteriovenous malformation resection by early career neurosurgeons: An observational study. Neurosurgery. 2019; 84:655-661.

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