Brain AVM: symptoms, causes, diagnosis and treatment

The Walton Centre says that in about 15% of cases AVMs do not cause symptoms and are found incidentally, for example on a scan done for another reason. The Brain Charity agrees that it is common to have no symptoms at all.

When symptoms occur they depend on the part of the brain involved. The Walton Centre describes the main patterns below.

• Haemorrhage (bleeding): more than 50% of AVMs are discovered after a bleed. Symptoms include a sudden severe headache, often with nausea, vomiting, neurological problems or a decreasing level of consciousness.

• Seizures: around 20% of AVMs are found because of seizures, because AVMs can irritate the brain.

• Headaches: these may be caused by the high blood flow through the AVM. They can be similar to migraine or actual migraines, and can be mild or disabling.

• Stroke-like symptoms: weakness or paralysis on one side of the body, numbness and tingling, and problems with vision, hearing, balance or memory, and personality changes.

• Noises in the head: some AVMs cause noises as blood flows through them. A dural arteriovenous fistula may cause a whooshing noise in time with the pulse (pulsatile tinnitus).

The Walton Centre explains that normally arteries carry oxygen-rich blood at high pressure into tiny capillaries, which slow the flow, and then into thin-walled veins that return blood to the heart. In an AVM that process is disrupted: arteries connect straight to veins through a tangle of poorly formed vessels called the nidus, with no capillary network between them.

AVMs vary in size. Some are small and others cover large parts of the brain. The Walton Centre says most do not grow or change much, although the vessels involved may widen, and less often they shrink if blood clots in part of the AVM. They are not cancerous or infectious and do not spread to other parts of the body.

The Walton Centre describes two types. The classic and more common type is a pial AVM. A dural AVM, more commonly called a dural arteriovenous fistula (dAVF), involves one or more direct connections between an artery and a vein, is less common and may form after head injuries, brain surgery, infections of the ear or brain, or blood clots in the large veins that drain the brain.

The Walton Centre says the cause of AVMs is not known. It is thought that AVMs are acquired, although some may form during development or shortly after birth, and it usually takes some time before they cause problems. The Brain Charity says people are usually born with an AVM.

The sources differ slightly on whether AVMs are present from birth, which reflects genuine uncertainty. Both agree that they are rarely hereditary. The Walton Centre says that where a genetic cause is found, the inherited condition is called hereditary haemorrhagic telangiectasia (HHT).

Bleeding is the most serious complication of an AVM. The Walton Centre says the risk is approximately 3-4% each year, increasing to about 6-7% for the next couple of years after a bleed. Some bleeds cause mild symptoms but approximately 50% are significant.

Because an annual risk is added up over many years, the question of whether to treat depends on the individual: the size, shape and position of the AVM, whether it has bled, and your age and wishes. The risk of treatment itself is part of that decision and should be discussed in detail with the specialist team.

The Brain Charity says your GP will note your symptoms and you will have CT and MRI scans. The Walton Centre describes three tests.

The Walton Centre explains that AVMs are complex and unique to each person, so management is individual. After the tests, your medical team meet with other experts in a multidisciplinary team (MDT) meeting to agree the safest and most appropriate plan. Treatment depends on the size, shape, position and blood supply of the AVM and how close it is to important parts of the brain that could cause lifelong disability if damaged. It also takes into account your health and your personal wishes, and no plan is made without discussing the options with you.

Treatment includes surgery, endovascular procedures, radiosurgery, or a combination of these. The Walton Centre says the risks of surgery are considered high for AVMs in deep parts of the brain or with very important functions nearby, and that some AVMs cannot be treated because the risk is too high. In that case you would be monitored with scans.

In surgery, you are asleep under general anaesthesia. The neurosurgeon temporarily removes part of the skull to reach the AVM, and with the help of a high-powered microscope seals off the AVM and removes it from the surrounding brain tissue. The skull bone is then reattached with small plates and the scalp closed. The Brain Charity says that where an AVM cannot be managed with regular scans, a doctor may refer for coiling surgery or a craniotomy to disconnect the AVM.

The sources read for this guide do not give success rates, so ask your team about the likelihood of complete removal and the risks for your AVM in particular.

A bleed from an AVM is an emergency. The Walton Centre describes a sudden onset of severe headache, often with nausea, vomiting, neurological problems or a decreasing level of consciousness. The NHS says to call 999 if you or someone you are with gets a sudden headache that is extremely painful and does not go away, has face weakness, weakness or numbness in one arm or down one side, speech problems, or blurred vision or loss of sight in one or both eyes. Do not drive yourself to A&E.

The NHS stroke advice uses the FAST check: face, arms, speech and time to call 999. It adds that symptoms can stop after a short time, but you should still get medical help straight away. A first seizure also needs medical assessment.

If you have a known AVM and develop a new or different pattern of headaches, new weakness, or any change in vision or speech, contact your specialist team or GP promptly, or NHS 111 if you cannot reach them.

The Brain Charity says it can provide practical and emotional support, including counselling, phone befriending and group therapy, for people with AVM from anywhere in the UK, and free support for carers, friends and family. It also points to the Butterfly AVM Charity and to an online community, AVM Survivors.

If you are being monitored rather than treated, it is normal to feel uneasy about what the scans may show. Ask your team how often you will be scanned, which symptoms should prompt contact, and whether anything affects driving or work. Our guide to seizures and driving rules explains the general position after a seizure.

On the NHS, brain AVMs are looked after by neurosurgical and neuroscience centres, with decisions made by a multidisciplinary team. A GP can refer you; an AVM found after a bleed or seizure is dealt with urgently through the emergency route.

Some people choose a private opinion or private scans. If you do, make sure the images and reports are shared with the NHS neurovascular team, because the MDT needs the full picture, and ask who would manage an emergency.