An arteriovenous malformation (AVM) is a tangled web of abnormal arteries and veins connected by fistulas (abnormal corridors). AVMs are thought to be present from birth and most commonly occur in the brain. AVMs can also occur in the spine, lungs, kidney, skin and, very rarely, limbs. Because some AVMs do not result in symptoms, the exact incidence is not known. AVMs of the brain that are detected are found in about 1 in 100,000 of the general population per year. AVMs affect both sexes and all ethnic groups.

Normally, oxygenated blood is carried by arteries to body tissues through ever smaller blood vessels. The smallest blood vessels are called capillaries and form the capillary bed which is where the exchange of oxygen and nutrients for carbon dioxide and other waste products produced by the body cells (cellular wastes) takes place. Following this exchange, the blood is carried away by progressively larger blood vessels, the veins. Because AVMs lack a capillary bed, arterial blood is shunted directly from the arteries into the veins via direct communications called fistulas.

The cause of AVMs is not known but it is thought that they develop as a result of a mistake in embryonic or fetal development.

Arteriovenous malformations of the brain

The main symptoms of brain AVMs include:

• Seizures/epilepsy;
• Brain haemorrhage;
• Focal neurological deficits in the absence of brain haemorrhage (most often weakness or numbness);
• Ringing in the ears (known as 'pulsatile tinnitus').

Further neurological effects that largely depend on the specific position of the AVM include:

• muscle weakness or paralysis;
• loss of co-ordination;
• dizziness;
• visual disturbances;
• problems in using or understanding language;
• numbness, tingling, or pain;
• memory deficits.

Vein of Galen malformation is a rare specific form of AVM.

There are three main methods of treating AVMs of the brain:

• Embolisation, in which particles are injected to block off the blood vessels of AVMs of the brain and dura (covering of the brain);
• Stereotactic radiosurgery, in which radiation is used to treat small vascular malformations, mainly AVMs less than three centimetres across;
• Neurosurgery, in which a surgical operation is performed on the brain to disconnect an AVM of the brain or dura (covering of the brain) from the arteries that supply it and the veins that drain it.

A combination of different treatments may be used, or in the case of embolisation, several separate treatments.

Inheritance patterns
Rarely, AVMs may occur in the brain and lungs as a result of a condition called Hereditary Haemorrhagic Telangiectasia.

Prenatal diagnosis
The presence of an AVM may be picked up on Ultrasound scan, although this is not usually the case.

Pulmonary arteriovenous malformations

As in AVMs of the brain, a pulmonary AVM is present at birth and the capillaries essential for the full oxygenation of blood are not present. Consequently, the normal oxygenation is not carried out properly as the exchange process of oxygen and nutrients for carbon dioxide and other waste products does not occur.

The effects of pulmonary AVMs include:

• Breathing difficulties;
• Shortness of breath on physical exertion;
• Cyanosis (bluish or purplish discoloration of skin or lips as a result of poor blood oxygenation);
• Clubbing (enlargement of the tips) of the fingers;
• Audible murmur when a stethoscope is placed over the AVM;
• Warmth of the overlying skin;
• Occasionally coughing up blood.

Some people with a pulmonary AVM do not have symptoms.

Diagnosis of a pulmonary AVM is made following tests which include, chest x-rays, chest CT (computerized tomography) scan, bubble echocardiogram (scan of the heart), perfusion lung scan (x-ray examination after injection of radioactive material) , pulmonary arteriogram (motion picture x-rays) or blood tests.

Treatment of pulmonary AVMs is by either surgical removal of the abnormal vessels and surrounding lung tissue or it might be possible to block the fistula with a coil when an ateriogram is carried out. If treatment is not carried out, there is a possibility of blood clots travelling from the lungs to the limbs or the brain. In the case of the latter, a stroke is a possibility.

Inheritance patterns
May be associated with conditions such as Hereditary Hemorrhagic Telangiectasia or Juvenile polyposis with hereditary hemorrhagic telangiectasia.

Prenatal diagnosis
This may be picked up on an ultrasound scan.

Spinal arteriovenous malformations

Spinal AVMs are very rare. They usually present to medical attention in adult life. They are a potentially treatable cause of myelopathy (any disease or disorder of the spinal cord). Myelopathies may cause any or all of the following symptoms:

• weakness of the legs;
• disturbance of sensation over the legs, buttocks and genital areas;
• impairment of bladder and/or bowel function.

Spinal AVMs usually involve the lower part of the spinal cord, called the thoracic cord which stretches from the neck to the small of the back.

Improvements in spinal cord imaging with Magnetic Resonance Imaging (MRI) have lead to quicker diagnosis. However, spinal AVMs are notoriously difficult to detect, and may require spinal catheter angiography (visualisation of the blood vessels after injection of a radiopaque substance) to be certain about the diagnosis.

Treatment of spinal AVMs is often difficult, and usually its objective is to limit further damage to the spinal cord, rather than alleviate the problems already caused. The two main forms of treatment are surgical excision and embolisation via a catheter in the groin. Embolisation is becoming the mainstay of treatment as technological advances in catheters and embolic glues are made.

Medical text written August 2005 by Contact a Family. Arteriovenous malformation of the brain and Spinal arteriovenous malformation information approved August 2005 by Dr R Al-Shahi, MRC Clinician Scientist and Specialist Registrar In Neurology, University of Edinburgh/ Western General Hospital, Edinburgh, UK. Pulmonary arteriovenous malformation information approved August 2005 by Dr A Jaffe, Consultant and Honorary Senior Lecturer in Respiratory Research, Great Ormond Street Hospital and Institute of Child Health, London, UK.

Further Online Resources
Medical texts in The Contact a Family Directory are designed to give a short, clear description of specific conditions and rare disorders. More extensive information on this condition can be found on a range of reliable, validated web sites and links to them are included in the CD-ROM version of this Directory. Further information on these resources can be found in our Medical Information on the Internet article.

AVM Support UK
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Tel: 01670 737231
e-mail: info@avmsupport.org.uk
Web: http://www.avmsupport.org.uk

AVM Support UK was, established in 2003 to offer free, patient friendly information and support to all whose lives have been affected Arteriovenous Malformations. AVM Support UK hosts an online meeting point for people with AVMs and provides access to reliable information.

Group details last updated August 2007.