Arterio-venous malformation (AVM) of the brain factsheet


An arterio-venous malformation (AVM) is a condition that happens in the tiny capillaries between an artery and a vein.

  • arteries are passages that carries blood away from your heart
  • veins are passages that carry blood towards the heart
  • capillaries are small blood vessels that join arteries and veins together.

In AVM, the capillaries can get bigger and get tangled up. When this happens, the pressure pushes blood through these bigger capillaries back to the heart instead of its normal pathway to the rest of the body. This means the heart must work harder, and the oxygen and nutrients in the blood do not reach parts of the body. 

AVMs can be found anywhere in the brain or spinal cord and can spread from the outer surface to the inner cavities, called ventricles.

AVMs are a congenital condition. This means they develop while a baby is growing during pregnancy.

 Signs and symptoms

Only a small number of children with AVM will show symptoms straight away. Many children never show any signs of symptoms.

Symptoms can include:

Most AVMs are found when there is bleeding in or around the brain.

A large AVM in a newborn baby can lead to heart problems caused by the increase in pressure.


See your local doctor as soon as possible if your child shows signs and symptoms of an AVM.

AVM is diagnosed by a doctor by:

  • listening to the head or neck with a stethoscope for a bruit – the sound of increased blood flow
  • doing a CT or MRI scan to get a picture of the inside of the head or spinal cord
  • doing an angiogram – where dye is injected into a blood vessel that goes to the brain.


How an AVM is treated will depend on:

  • where they are in the body
  • how big they are
  • the symptoms they are causing.

Treatment of AVM can be complicated. It can include:

  • surgery – removing the abnormal capillaries
  • radiosurgery – using radiation to damage the abnormal capillaries
  • endovascular treatment – inserting a small tube into the abnormal capillaries and blocking them with a special substance
  • a combination of all the above.


Vein of Galen Malformation

The vein of Galen Malformation is a rare condition where an AVM forms in one of the large veins of the brain. This stops cerebrospinal fluid from flowing properly.

Cerebrospinal fluid is the watery fluid that flows in and around the brain and spinal cord. It gives protection and nourishment to the brain and takes away waste.

When the cerebrospinal fluid builds up, pressure increases and can cause the ventricles to get bigger. This can lead to a condition called Hydrocephalus. Hydrocephalus causes the head to swell and can cause severe brain damage.

Resources and more information

Last updated Tuesday 5th March 2024


This factsheet is provided for general information only. It does not constitute health advice and should not be used to diagnose or treat any health condition.

Please consult with your doctor or other health professional to make sure this information is right for you and/or your child.

The Sydney Children’s Hospitals Network does not accept responsibility for inaccuracies or omissions, the interpretation of the information, or for success or appropriateness of any treatment described in the factsheet.

© Sydney Children’s Hospitals Network 2024