What is an arteriovenous malformation?

Typically arteries carry blood with oxygen from the heart to the brain and veins carry blood with less oxygen away from the brain and back to the heart. An arteriovenous malformation, also known as AVM, involves a tangled nest of blood vessels that bypasses normal brain tissue and directly diverts high pressure blood from the arteries to the veins. 

How common are brain AVMs?

Brain AVMs are more common in males than in females and occur in less than 1% of the population. 

Why do brain AVMs occur?

Brain AVMs are thought to be congenital, meaning it is a condition someone is born with or that it develops during childhood. However, brain AVMs are not usually hereditary. Brain AVMs can occur anywhere within the brain or spine. 

What are the symptoms of a brain AVM?

Specific symptoms will vary depending on the location of the AVM. Potential symptoms may include: 

  • Many patients will have minimal or no symptoms. 
  • Some patients will report intermittent headaches. 
  • Some patients may experience stroke-like symptoms including focal numbness, weakness, visual changes or difficulty speaking.
  • 20% to 25% of AVM patients have a seizure or epilepsy from the AVM.
  • If the AVM ruptures and bleeds there can be severe, sudden onset symptoms such as severe headache, seizures, paralysis, confusion, vomiting or lethargy. A ruptured brain AVM is an emergency situation. 

What causes brain AVMs to bleed?

A brain AVM is a nest of abnormal, weakened blood vessels that direct high pressure blood away from normal brain tissue. These blood vessels over time may rupture from the high pressure of blood within the malformation. A ruptured AVM is a life threatening emergency and will cause bleeding within the brain. The extent of brain injury is proportional to how much bleeding has occurred and which part of the brain is affected.

The risk of a brain AVM bleeding is approximately 1% to 3% each year. The risk of death from a brain AVM bleeding is 10% to 15% per episode of bleeding. Meanwhile, the chance of permanent brain damage is 20% to 30% per episode of bleeding. When blood leaks into the brain, normal brain tissues are damaged. This brain tissue damage results in a loss of normal function, which may be permanent or temporary. 

Are there different types of brain AVMs?

Below are the following types of brain AVMs:

  • True arteriovenous malformation: This is the most common type of brain vascular malformation. It consists of a tangling of abnormal vessels that connect arteries and veins with no normal intervening brain tissue. 
  • Cavernous malformations/ cavernoma : This is a low flow vascular malformation in the brain that does not actively divert large amounts of blood. This condition may cause bleeding and produce seizures. 
  • Venous malformation: This condition only involves an abnormality of the veins that is typically congenital and has a very low risk of bleeding. 
  • Dural arteriovenous fistula: This consists of an abnormal connection between blood vessels that involve only the surface covering of the brain. 

How are AVMs diagnosed?

Most AVMs are diagnosed with either a CT scan or an MRI scan. An angiogram may be needed in order to better identify the type of AVM, its size and a detailed analysis of the AVM structure.. 

What is the best treatment for an AVM?

There are different medical treatments for an AVM. The following treatment options include:

  • Medical therapy: Conservative treatment, such as controlling blood pressure, seizures and observing for any new symptoms over time.
  • Surgical removal of the AVM: Surgery may be recommended if an AVM has bled or if it is in an area that can be easily accessed. 
  • Stereotactic radiosurgery: If an AVM is not too large, but is in an area that is difficult to reach via regular surgery, it may be treated with stereotactic radiosurgery. This treatment does not involve any incisions. The procedure involves performing a cerebral angiogram to localize the AVM. Then, focused-beam high energy sources are concentrated on the AVM. The AVM may be gone in 2-3 years after radiosurgery.
  • AVM embolization: A minimally invasive procedure in which small catheters are used to fill portions of the AVM with “glue”, or liquid embolic agent. The AVM is shrunken gradually by embolizing and blocking the feeding arteries. Embolization can be done as part of a multistage treatment plan that later involves surgery or radiation treatment.

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