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Brain Arteriovenous Malformations (AVM)


A brain arteriovenous malformation, referred to as a 'brain AVM' is where the blood vessels in the brain are tangled together.

In the body and in the brain, arteries deliver oxygenated blood to the cells in individual organs from large arteries to smaller arterioles and eventually capillaries, while the veins take the deoxygenated blood from the organs to the heart and lungs through small venules and then larger veins, and then the cycle continues. A brain AVM 'bypasses' brain tissue, where blood flows directly from the arteries to the veins without passing through the brain capillaries. Generally, brain AVM do not change over time. However, they are still subject to changes that can affect any blood vessels (e.g. rupture), as well as recruitment or involvement of new blood vessels and development of AVM-related aneurysms.

Brain AVM's are relatively rare and are estimated to affect 1 in 2,000-5,000 people. Men are slightly more likely to have an AVM than women. Symptoms indicating a possible AVM tend to become apparent in people aged 10-40. Often brain AVM is discovered when brain scans for other conditions.


Why brain AVM's form is not fully understood. It is generally believed that most people with brain AVM's are born with them (i.e. it is a congenital defect which occurs during the development of the foetus). However, the condition is not commonly diagnosed in infancy, and some researchers believe that AVM’s may develop in childhood. Most brain AVMs are not associated with inherited factors, although a genetic condition is linked to higher risk of brain AVMs (Hereditary Haemorrhagic Telangiectasia), which is also associated with lung AVMs.


Brain AVM will often have no symptoms, unless there is a rupture and bleed into the brain. If this occurs, this can lead to sudden headache, stroke-like symptoms or loss of consciousness. Another common symptom is a first-time seizure. Other symptoms that can occur include…

  • Headache (often severe, and often affecting just one part of the head).
  • Weakness / numbness in a specific part of the body (dependent on the area of the brain affected).
  • Vision/speech difficulties.
  • Unsteadiness (often severe).
  • Mental issues (e.g. confusion, problems understanding).

Tests / Diagnosis

After an initial review of symptoms, medical history and physical examination, the following diagnostic tests may also be used…

  • CT (computed tomography) or CT angiogram scan (involving dye injection).
  • MRI (magnetic resonance imaging) and MR angiogram scan.
  • Cerebral arteriography / angiography - this allows the visualisation of the blood vessel structure in the brain. It is a form of x-ray imaging using an injection of special dye to highlight the blood vessel structure.

Related Information

AVM, DAVF and CCF - Embolisation AVM and DAVF - Microsurgery