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Venous malformations

What are venous malformations?

A venous malformation (VM) is a tangled network of veins that developed abnormally. Veins are the vessels that carry deoxygenated blood back to the heart.

People with VMs are born with them, but the condition may go undetected until later in life. The abnormal veins grow as the child grows. They may also swell temporarily during exercise, while straining, or when the child is in certain positions.

Most VMs are near the skin, but they can develop anywhere in your child's body, including muscles, organs or bones. In the vast majority of cases, the child has only one VM. However, some children have multiple VMs in different areas of the body.

VMs are a type of vascular malformation, a term used to describe blood vessels that didn't develop correctly.

Causes of venous malformations

While some forms can be inherited, most VMs occur spontaneously. Experts have linked VMs to mutations in several different genes.

Symptoms of venous malformations

Venous malformations in or near the skin can make the skin look blue or purple, similar to a bruise. If the VM is deeper in the body, you may see a soft bulge but no skin discoloration.

Calcified blood clots called phleboliths may form inside a VM. If you can press down on a VM, you may feel these small, hard bumps.

Symptoms of a VM vary depending on its size and location. They may include:

  • Pain, especially if the VM involves a muscle, tendon or joint
  • Bleeding
  • Difficulty speaking or eating if the VM is in the mouth
  • Bloody stools (poop) if the VM is in the intestines or bloody urine if it's in the bladder

Diagnosis of venous malformations

To diagnose a VM, your child's doctor will perform a physical exam, review your child's health history and, if needed, order imaging tests, such as an ultrasound or MRI.

Treatment of venous malformations

Some VMs cause no problems and require no treatment. However, if the VM is causing pain, disfigurement or impairment, your child's care team may recommend one or more of these treatment options:

  • Compression garments. Special tight-fitting clothing can reduce pain, swelling and the risk of thrombosis (formation of blood clots).
  • Medications. Aspirin, other anti-inflammatory drugs, or anticoagulant (blood-thinning) medications may be used for pain.
  • Sclerotherapy. In this procedure, a doctor injects a chemical solution into the abnormal veins, causing them to shrink.
  • Surgery. Some VMs can be removed surgically. Your child may need sclerotherapy before the surgery.

People with VMs need regular follow-up care. A VM may grow during times of hormonal change, such as puberty or pregnancy, and begin causing symptoms. Also, VMs can grow back after treatment.

UCSF Benioff Children's Hospitals medical specialists have reviewed this information. It is for educational purposes only and is not intended to replace the advice of your child's doctor or other health care provider. We encourage you to discuss any questions or concerns you may have with your child's provider.

Where to get care (1)


Birthmarks & Vascular Anomalies Center

Birthmarks & Vascular Anomalies Center

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San Francisco, CA 94158

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