What Are Arteriovenous Malformations (AVM)?
An arteriovenous malformation (AVM) is an abnormal connection between arteries and veins. In the normal circulation system, blood travels from arteries into capillaries and then into veins. Some arteriovenous malformations (AVMs), commonly seen on the head and neck, can appear as light stains at birth. Other types of AVMs, commonly seen on the trunk or on a limb, may not be noticed until later in childhood.
AVMs may occur in our soft tissues like skin, fat and muscles as well as in organs such as the brain, lung, liver and intestines. Lesions within the brain are the most common arteriovenous malformation. AVMs in the brain sometimes do not cause any symptoms but may cause issues as the AVM becomes larger and can be life-threatening.
It is unknown what causes AVMs. Individuals with conditions like hereditary hemorrhagic telangiectasia (HHT) or capillary malformation-arteriovenous malformation (CM-AVM syndrome) and those with certain genetic abnormalities like RASA1 mutations are more likely to have AVMs. There are additional genetic abnormalities that are connected with AVMs in the brain.
What do AVMs look like?
AVMs can appear in many different ways.
Often, an AVM cannot be seen. However, when there is soft tissue involvement, these malformations show up as a light red-pink color in infancy and childhood. With age, the skin becomes a darker red or purple color, and a firm mass appears below the area of skin discoloration.
If you rest your hand over the lesion, you will feel increased warmth (compared to nearby skin) and sometimes feel pulsation of the blood.
When in the arm or leg, the one with the AVM in it may be larger than the unaffected limb.
How are AVMs diagnosed?
Physical examination shows that the skin covering the lesion is warm or hot to touch. Pulsation of blood flow can be felt, and an audible noise can be heard with a stethoscope.
Figuring out the extent of the lesion and identifying the core (called a “nidus”) is done through magnetic resonance imaging (MRI), magnetic resonance angiography (MRA; a specific type of MRI that looks at the flow of blood in vessels), or traditional angiography. Tests are essential for diagnosis and treatment planning.
Conditions Involving Arteriovenous Malformations
Hereditary Hemorrhagic Telangiectasia (HHT)
A genetic disorder called hereditary hemorrhagic telangiectasia (HHT) or Osler-Weber-Rendu syndrome is characterized by multiple, small arteriovenous lesions. These lesions can occur in the skin, mucous membranes (mouth, nose, and gastrointestinal tract), lungs, liver, brain, and other sites. Patients usually present with telangiectasias (small dilated blood vessels)) of the skin and mucous membranes, and nosebleeds. Some people may have AVMs within their internal organs. At least three genes are known to cause this condition. It is usually inherited from one parent.
Capillary Malformation-Arteriovenous Malformation (CM-AVM) syndrome
Capillary Malformation-Arteriovenous Malformation syndrome (CM-AVM) is a genetic disorder that affects the blood vessels. In CM-AVM, certain types of blood vessels (capillaries) are enlarged, with multiple capillary malformations visible on the skin. There can also be abnormal connections between blood vessels, resulting in AVMs. These AVMs can be internal, in the brain and spine, or can occur in the skin, muscle or bone on the trunk, or in a limb as part of Parkes Weber syndrome (see below).
Parkes-Weber syndrome involves AVMs of an extremity, most commonly the leg. These patients also may have lymphatic malformations. The affected limb usually has a capillary malformation visible on the skin and is larger than the unaffected leg. The AVM of the leg may put extra stress on the heart. If untreated, this can result in heart issues that can become very serious.
Multiple tests such as MRI and MRA, CT imaging, ultrasonography (ultrasound) and echocardiogram (ECHO) are used to evaluate and monitor these syndromes. Treatment depends on each patient but may include medications and surgical procedures.
What are possible complications of AVMs?
Possible complications of AVMs include breakdown of overlying skin with bleeding, pain, and risk of infection. Extra stress on the heart may cause heart enlargement and could lead to heart failure over time.
A few common AVM locations are:
Lungs – When AVMs are present in lungs, there is also a risk for stroke or brain abscess (infection). There is also a risk for bleeding when there is AVM involvement in the lung. The highest risk occurs during pregnancy when the mother’s blood pressure and blood volume increase.
Brain – Brain AVMs can bleed, causing neurologic problems such as seizures or stroke. Signs may include dizziness, headache, or visual changes. Any changes in mental status or alertness need immediate evaluation.
Liver – Most individuals with liver AVMs do not require treatment because they rarely bleed or cause any other medical problems. Later in life, liver or heart failure can occur.
Treatment and Management
Should my child receive treatment?
Individuals with AVMs or suspected AVMs should visit an AVM specialist. Treatment decisions must be made on an individual basis.
How are AVMs managed?
Management of AVMs depends on individual symptoms and potential complications. Both surgical and non-operative approaches are used. AVMs generally require evaluation and treatment by a multidisciplinary team of experts. Regular follow-up is important to monitor and manage complications.
- Observation. Small lesions without symptoms are observed over time.
- Supportive care. All patients with lung AVMs require preventative antibiotics for dental procedures (including routine cleaning). Some surgical procedures, such as scopes of the digestive and reproductive tracts, should have antibiotics as well. This involves taking a single larger dose of antibiotic by mouth one hour prior to the procedure.
- Drug therapy. Some medications that have been used include doxycycline, thalidomide and its derivatives, bevacizumab, and pazopanib. The choice of medicine may be directed by the genetic cause of the AVM.
- Surgical removal. This approach may be possible with certain lesions. When combined with preoperative embolization, removal offers the best chance for cure. If the core of the lesion is completely removed, the lesion may never return. If complete removal of the core is not possible, the lesion may return or cause similar or different issues.
- 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. This is often used with the lesions are larger, and surgery is not an option.
Are there any risks associated with treatment?
Treatment is aimed to prevent future issues and improve the functioning and emotional well-being of the individual. Despite these benefits, each treatment approach has drawbacks and limitations.
- Drug therapy. As with any medication, these medications have potential side effects. Prior to starting any medication, your provider will review side effects.
- Surgical removal. Some degree of scarring will occur with surgery. Surgical interventions may also cause damage to structures involving or near the malformation. Bleeding during surgery is a potential complication.
- Embolization. Most patients do not have problems or serious side effects. Bleeding or bruising can occur at the catheter site. Clotting of an artery or damage to normal tissue is also possible.