Arteriovenous Malformation (AVM)

What an AVM is

Normally, high-pressure arteries branch into tiny capillaries that slow blood flow and allow oxygen and nutrients to reach tissues before blood drains into veins. In an AVM, arteries feed directly into a tangle of abnormal vessels (the nidus) that drains straight into veins.

This causes problems because:

• veins receive high-pressure arterial blood, so their walls stretch and can rupture
• surrounding brain tissue may be starved of blood ("steal")
• abnormal flow can irritate the brain and trigger seizures

Brain AVMs are thought to form during development before birth, though they may change over life. They are found in roughly 1 in 1,000 people or fewer and are usually diagnosed between ages 20 and 40. Most occur sporadically. Multiple AVMs suggest an inherited condition, especially hereditary hemorrhagic telangiectasia.

Symptoms

Many AVMs cause no symptoms and are discovered on a scan done for another reason. When symptoms occur, they include:

• Bleeding (hemorrhage): the first sign in about half of people with brain AVMs. It causes a sudden severe headache, vomiting, confusion, seizures, weakness or loss of consciousness. See intracerebral hemorrhage.
• Seizures: the second most common presentation; may be focal or generalized.
• Headaches: sometimes migraine-like, often on the same side as the AVM.
• Progressive neurological deficits: weakness, numbness, vision or speech problems.
• Pulsatile tinnitus: a whooshing sound with the heartbeat.

Spinal AVMs cause back pain, gradually progressive leg weakness, numbness, and bladder and bowel problems.

AVMs elsewhere in the body can cause skin discoloration and swelling (limbs), bleeding (gut), or low oxygen levels and strokes (lungs).

Bleeding risk

An unruptured brain AVM bleeds at an average rate of about 2 to 4% per year, which adds up over a lifetime. The risk is higher with:

• a previous bleed (the greatest risk factor, especially in the first year after)
• deep location (basal ganglia, thalamus, brainstem)
• drainage only into deep veins
• an associated aneurysm on feeding arteries

About 1 in 10 bleeds is fatal, and many survivors have lasting disability, though AVM bleeds are often less severe than bleeds from other causes.

Diagnosis

• CT scan: detects bleeding quickly in an emergency.
• MRI and MR angiography: show the AVM's size, location and effects on brain tissue.
• CT angiography: a fast way to show the vessels.
• Catheter (digital subtraction) angiography: the gold standard, mapping feeding arteries, the nidus and draining veins in detail; needed to plan treatment.
• EEG if seizures occur.

Doctors grade brain AVMs using the Spetzler-Martin scale, which scores size, whether the AVM is in an "eloquent" brain area (controlling movement, speech, vision or sensation), and venous drainage pattern. Higher grades carry higher surgical risk.

Treatment

Decisions are made by a specialist team of neurosurgeons, interventional neuroradiologists and radiation oncologists, balancing the lifetime bleeding risk against treatment risks.

Microsurgical resection

Surgically removing the AVM offers immediate cure when complete. It is preferred for small, superficial, low-grade AVMs, especially after a bleed.

Stereotactic radiosurgery

Focused radiation (Gamma Knife, CyberKnife or linear accelerator) damages the vessel walls so the AVM gradually closes over 2 to 3 years. It suits small (under about 3 cm), deep AVMs. Bleeding risk remains until closure is complete.

Endovascular embolization

A catheter is threaded through blood vessels to the AVM, and glue-like agents or coils block feeding vessels. It is mostly used before surgery or radiosurgery to make them safer, and occasionally as the sole treatment for small AVMs.

Observation

For some unruptured AVMs, especially high-grade ones in critical areas, the risks of treatment may exceed the risk of bleeding. A major trial (ARUBA) suggested that medical management alone led to fewer strokes and deaths over several years than intervention for many unruptured AVMs, though its findings are debated and decisions remain individual.

Managing symptoms

• antiseizure medicines for seizures, as in epilepsy
• control of blood pressure
• avoiding smoking and stimulant drugs

Outlook

Outcomes depend on whether the AVM has bled, its location and treatment. Once completely removed or closed, the AVM is considered cured and the bleeding risk falls to near zero. People with untreated AVMs need regular follow-up and should know the warning signs of bleeding.

Frequently asked questions

What are the symptoms of a brain AVM?

Many cause no symptoms. When they do, the most common are a sudden severe headache from bleeding, seizures, recurring headaches, and gradual weakness, numbness, vision or speech problems. Some people hear a whooshing sound in time with their heartbeat.

What causes an arteriovenous malformation?

Most AVMs develop before birth for reasons that are not fully understood and are not caused by anything a person or parent did. Multiple AVMs can occur with inherited conditions such as hereditary hemorrhagic telangiectasia. Injury rarely causes a similar abnormal connection called a fistula.

How dangerous is an AVM?

The main danger is bleeding. Unruptured brain AVMs bleed at about 2 to 4% per year on average, with higher risk after a previous bleed. Bleeds can cause disability or death. Many people live for years without problems, and treatment can remove the risk in suitable cases.

Can an AVM be cured?

Yes, in many cases. Complete surgical removal, or full closure after radiosurgery or embolization, eliminates the AVM and its bleeding risk. Not all AVMs can be safely treated, particularly large ones in critical brain areas, and these are often monitored.

Can I exercise with an AVM?

Most people with unruptured AVMs can do moderate exercise. Some specialists advise avoiding heavy straining, contact sports or activities that sharply raise blood pressure. Ask your neurosurgeon for advice specific to your AVM's size, location and treatment status.