Arteriovenous malformation (AVM): symptoms, causes and treatment

The Walton Centre explains that arteries normally carry oxygen-rich blood under high pressure and flow into capillaries, which slow the blood before it passes to veins. In an AVM this process is disrupted by a tangle of abnormal blood vessels called the nidus. Northern Care Alliance NHS Foundation Trust adds that high-pressure blood enters veins that are not built to withstand it, and the arteries tend to be larger and can develop areas of weakness, so some AVMs can burst.

AVMs can occur anywhere in the body but those in the brain are of particular concern because of the problems they cause if they bleed. The Walton Centre says most do not grow or change much, although the vessels may widen, and occasionally they shrink if blood clots in part of the AVM. A dural AVM, also known as a dural arteriovenous fistula, is a less common type involving connections between an artery and a vein, which may form after head injury, brain surgery, ear or brain infections or blood clots in the large veins draining the brain.

The Walton Centre says in about 15% of cases AVMs do not cause symptoms and are found incidentally. Otherwise symptoms depend on the part of the brain involved:

• Haemorrhage: sudden severe headache, often with nausea, vomiting, neurological problems or a decreasing level of consciousness. More than 50% of AVMs are discovered after a haemorrhage.

• Seizures: found in approximately 20% of cases at diagnosis, because AVMs can irritate the brain.

• Headaches: may be similar to migraine or be actual migraines, mild or disabling, because of high blood flow through the AVM.

• Stroke-like symptoms: weakness or paralysis on one side, numbness and tingling, and problems with vision, hearing, balance, memory and personality, when nearby tissue is deprived of oxygen.

• Noises in the head: a whooshing sound in time with the pulse, particularly with dural AVFs.

The Walton Centre says the blood vessels in an AVM are weaker and at a higher risk of bleeding than normal ones, that bleeding is the most serious complication and the main reason for recommending treatment. The risk of bleeding is approximately 3 to 4% each year, increasing to about 6 to 7% for the next couple of years after a bleed. It says some bleeds cause mild symptoms but approximately 50% are significant.

Northern Care Alliance says a brain haemorrhage from an AVM affects a person suddenly and usually without warning, and that how someone is affected depends on the size and location of the bleed.

The Walton Centre lists a CT scan (with or without dye) to look for bleeding and view the AVM, an angiogram in which dye is injected into the brain's blood vessels via a catheter from the groin or wrist to show its exact location, shape and size, and an MRI scan to show its position relative to other structures. A functional MRI may be used if the AVM is close to areas controlling vision or movement, so that doctors can judge how safe treatment would be.

Northern Care Alliance says that after a bleed the haemorrhage is confirmed by a CT scan, and the cause is usually found by a CT angiogram, sometimes followed by MRI and a catheter angiogram.

The Walton Centre says AVMs are complex and unique to each person, so management is individual. A multidisciplinary team of experts meets to make the safest plan, considering the AVM's size, shape, position and blood supply, how close it is to important parts of the brain, and your health and wishes. No treatment plan is made without discussing the options with you. Northern Care Alliance says treatment is only considered if the benefits outweigh the risks, because any treatment on brain blood vessels carries risk of serious complications including stroke and death.

Northern Care Alliance says the time it takes to recover after an AVM haemorrhage is very variable, with a minimum of 4 to 6 weeks and possibly many months. Treatment is usually planned for a time after the blood from the presenting haemorrhage has settled, which may be a few weeks. Complications in hospital can include hydrocephalus, where fluid builds up around the brain and may need a drain or shunt, and seizures, which can usually be controlled with medicine.

It says everybody who has had a brain haemorrhage and holds a driving licence must inform the DVLA, which is a legal requirement, and that otherwise insurance may be void and you may be liable to prosecution. It also says you can fly once you are fit enough, and that if you are thinking of becoming pregnant you should discuss it with your doctor or specialist nurse.

A sudden, severe headache, especially with vomiting, collapse, a seizure, weakness, or problems with speech or vision, should be treated as an emergency: call 999. Northern Care Alliance describes an AVM bleed as affecting a person suddenly and usually without warning.

The Walton Centre says AVMs affect men and women equally and occur in all races, and that rarely they are hereditary with a genetic cause that can be found: this inherited condition is called hereditary haemorrhagic telangiectasia (HHT).

AVMs are managed by specialist neurovascular teams in neurosurgical centres. A GP or emergency department refers you, and the plan is agreed at a multidisciplinary meeting. Some people seek a private second opinion; ask for scans to be shared with the NHS team and for each option's risks to be explained in numbers where possible.