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CM-AVM (Capillary Malformation-Arteriovenous Malformation Syndrome)

What is Capillary Malformation-Arteriovenous Malformation Syndrome?

Capillary Malformation-Arteriovenous Malformation Syndrome (CM-AVM) is a genetic condition that affects the blood vessels. In CM-AVM, certain types of blood vessels (capillaries) are enlarged. There can also be abnormal connections between blood vessels.

Common signs of CM-AVM

Multiple capillary malformations (CMs)

  • CMs are flat, pink or red spots on the skin. The skin discoloration comes from the abnormal blood vessels. The spots lighten when pressed and then refill with blood. Most people with CM-AVM will have at least one capillary skin lesion. These lesions may be there at birth or they can also develop as a person ages. CMs are most common on the face, trunk, legs, and arms.

Arteriovenous Malformations (AVM) or Fistulas

  • AVMs happen when an artery (a blood vessel that pumps blood to the body parts) is not normally connected to a vein (a blood vessel that brings blood back to the heart and lungs). AVMs are usually found in the skin, muscle, bone, brain, or spine. AVMs may or may not be visible, depending on their location. People with CM-AVM have about a 30% chance of having an AVM.
  • AVMs in the brain or spine cannot be seen, so you may not know you have them. Imaging, such as MRI, is often needed.
  • AVMs of the skin, soft tissue (fatty layer under the skin), or muscle can sometimes be seen on physical exam. They often have a CM over the area or cause overgrowth. When a person has overgrowth in an arm or leg due to an AVM and an overlying CM, they are diagnosed with Parkes-Weber syndrome. Parkes-Weber syndrome is a sub-type of CM-AVM.

Other Symptoms

  • An increased chance of nosebleeds. How often nosebleeds occur is variable.
  • An increased chance of telangiectasias. They look like tiny red freckles. Like CMs, they also lighten when under pressure and new ones can appear as a person ages.
  • An increased chance of Bier spots. Bier spots are white or pale spots on the skin which can cause a mottled appearance.

Up to one in 12,000 people have CM-AVM. CM-AVM is under-diagnosed because people and doctors are not aware of the symptoms. CM-AVM may be found when AVMs cause symptoms or when multiple CMs are noticed. A diagnosis of definite or probable CM-AVM has been suggested when someone has the signs below.

Definite CM-AVM Multiple CMs OR a change in one of the two genes that causes CM-AVM
Probable CM-AVM More than three CMs OR
At least one CM AND an AVM OR a family history of CMs

*These criteria do not consider telangiectasias, nosebleeds or a family history of AVMs. CM-AVM or Hereditary Hemorrhagic Telangiectasia (HHT) should also be considered with these signs.

Causes of CM-AVM

CM-AVM is caused by changes in the RASA1 and EPHB4 genes. Changes in RASA1 are called CM-AVM1. Changes in EPHB4 are called CM-AVM2. People with CM-AVM2 may have a lower chance of brain or spine AVMs; however, vein of Galen malformations may be more common. People with CM-AVM2 may also be more likely to have nosebleeds, telangiectasias, and Bier spots.

A related condition, HHT, is caused by genetic changes in three to four other genes. These genes are called ENG, ACVRL1, SMAD4, and GDF2. People with CM-AVM may be misdiagnosed with HHT or vice versa.

Genetic testing can determine if you have a change in the CM-AVM genes. If testing is positive, it means you have CM-AVM, even if you do not have all of the symptoms. If testing is negative, you may still have CM-AVM.

CM-AVM can originate in different ways:

  1. It may be inherited from a parent who has CM-AVM. A person with CM-AVM has a 50% chance of passing it on to their children.
  2. It may not be inherited from a parent. The condition could be new - sporadic or mosaic. The chance for parents to have another child with CM-AVM depends on whether the condition was sporadic or mosaic in their child.

Possible Complications

Several complications are possible with CM-AVM:

  • Brain / Spine AVM: Brain AVMs can bleed, causing neurologic problems. Symptoms may include dizziness, headache, changes in vision, seizures, paralysis and stroke.
  • AVMs in other parts of the body: Some people will have an AVM in another part of the body, like the skin, muscles or bone. These AVMs may cause that part of the body to be larger and may put extra stress on the heart. Skin around the AVM can break down, leading to scabbing or bleeding. These wounds may be difficult to heal. This is commonly called Parkes-Weber syndrome.
  • CMs: CMs without an underlying AVM are not likely to cause health problems.



  • Laser treatment may be used to lighten the color of the CM. However, it may not be as effective on CMs associated with CM-AVM.


  • Observation: AVMs that are small or in sensitive areas may be observed for changes or growth over time.
  • Surgical excision (removal): This approach may be possible with certain lesions. The lesion is removed using surgical instruments. The location of the AVM and the risks to removing it help doctors decide if this is the best option.
  • Embolization: Embolization is an injection of material into the center of the lesion to block the blood supply to the lesion. There are several different materials that interventional radiologists can use for embolization.
  • Stereotactic radiosurgery (SRS): Focused radiation is used to destroy the AVM.

CM-AVM Resources

Because CM-AVM can affect many systems of the body, people need a team of doctors and health care workers to treat the syndrome. The Cincinnati Children's HHT Center is made up of specialists from a wide variety of backgrounds who care for both children and adults with CM-AVM.

Other resources to help parents and families find out more about CM-AVM include:

Last Updated 03/2023

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