Arteriovenous Malformations

An arteriovenous malformation is a localized or diffuse vascular lesion consisting of direct connections between arteries and veins, with the absence of the intervening capillary bed (network of tiny capillaries) that normally connects these vessels.

Localized lesions, most commonly seen on the head and neck, often appear as light vascular stains at birth and generally do not enlarge until early childhood or adolescence.

Diffuse lesions, commonly seen on the chest and abdomen or on a limb, may not be observed until later in childhood, as they enlarge with age.

Both localized and diffuse lesions are seen in internal organs such as the brain, lung, liver and bowel. Lesions within the brain are the most common arteriovenous malformation. They are initially silent, with symptoms depending upon the rapidity of enlargement.

While the precise cause of all arteriovenous malformations is unknown, they are thought to be caused by errors in the formation and development of the normal arterial-capillary-venous connections that occur very early in embryonic life. However, the differing patterns of growth and microscopic presentation in localized and diffuse lesions indicate other additional causes for the latter.

Some arteriovenous malformations can be associated with genetic abnormalities such as PTEN mutations and Rasa.1 mutations.

The association of diffuse AVMs with PTEN mutations has been documented in numerous case reports in the literature. The PTEN gene is involved in normal vascular development. A mutation in PTEN would, therefore, result in abnormal angiogenesis, thus explaining the incidence of AVMs.

There is no evidence that drugs or medications taken during pregnancy or environmental exposures that may have occurred during that time can cause arteriovenous malformations.

Due to differences in position, size, length and number of arteriovenous malformations, there are wide variations in appearance.

In many cases, there is no visible abnormality. However, when there is soft tissue involvement, these malformations generally show an overlying blush color in infancy and childhood.

With age, the skin becomes a darker red or purple color, and a firm mass appears beneath the stain.

If you rest your hand over the lesion, you will feel warmth and sometimes feel pulsation of the blood as it rushes through the vessels.

Physical examination reveals that the skin overlying the lesion is warm.

Also, pulsation of blood flow can often be felt and an audible bruit (noise) can be heard with a stethoscope.

Determining the location of the core of the lesion and the extent of the lesion 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. These tests are essential both for diagnosis and treatment planning.

Complications can include ulceration, bleeding and persistent pain. If the blood flow through an arteriovenous malformation is excessive, the heart will enlarge over time due to the persistence of forcing extra blood through the AVM, and this may result in a type of heart failure.

A few common AVM locations are: 

Lungs – There is always a risk for rupture when there is AVM involvement in the lung, however this mostly occurs during pregnancy as blood pressure and volume are likely to increase. In these situations, there is also a risk for stroke or brain abscess due to the loss of the capillary ability to filter for impurities such as clots, air bubbles and bacteria. 

Brain Brain AVMs can bleed, causing neurologic compromise. Signs may include dizziness, headache, or visual changes. 

Liver Most individuals with liver AVMs are not treated because they rarely bleed or cause any other sudden medical complications. In occasional instances, later in life, liver or heart failure can occur.

Observation Small asymptomatic lesions are sometimes just observed over time without intervention. 

Medications – The biology of AVMs is being investigated so that medical options may be available for treatment. Some medications that have been used include Doxycycline, Thalidomide and Rapamycin. 

Surgical excision (removal) – This approach alone is more likely to be successful with localized lesions. When combined with preoperative embolization, it offers the best chance for cure. If the core of the lesion is completely removed, the lesion may never recur. When the location and extent of the arteriovenous malformation make removal of the entire core of the lesion impossible, the lesion may recur. 

Embolization For more extensive lesions and/or when lesions are diffuse and surgery is not possible, embolization may improve overall quality of life by controlling the lesion and lessening the symptoms for a period of time. 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.

Hereditary Hemorrhagic Telangiectasia (HHT)

A genetic disorder called hereditary hemorrhagic telangiectasia (HHT) or Rendu-Osler syndrome is characterized by multiple, small arteriovenous lesions that can occur in the skin, mucous membranes (mouth, nose, and gastrointestinal tract), lungs, liver, brain, and other sites.

Three genes are known to cause this condition, all of which result in the dysfunction of cell receptors. In HHT, arteriovenous malformations usually present with telangiectasia (permanent widening of groups of superficial capillaries and tiny veins) of the skin and mucous membranes. Bleeding typically occurs during and after puberty, and treatment is aimed at minimizing bleeding. In cases of nosebleeds, laser treatment of the nasal septum (thin membrane between nostrils) can be quite helpful. However, medical therapies with injectable agents such as Avastin are presently being used for nosebleeds. 

Parkes-Weber Syndrome

Parkes-Weber syndrome involves diffuse arteriovenous malformations of a limb with overgrowth of the limb. These patients also may have lymphatic malformations. The affected limb usually has a capillary malformation involving skin. The heart may be affected secondary to increased blood flow in the involved area of the body. If untreated, this can result in an enlarged heart and eventually in heart failure.

MRI and MRA are the most appropriate diagnostic techniques. Some patients also must undergo an echocardiogram to monitor the status of the heart. 

Treatment may include embolization and, in some patients, surgical procedures. 

CLOVES

CLOVES syndrome involves arteriovenous malformations, which are often rare and aggressive when involved with CLOVES. These AVMs may also be found as a high-flow aggressive spinal lesion, which can cause serious neurological deficits or paralysis.

CLOVES is a congenital syndrome that includes lipomatous tissue overgrowth, vascular malformations, epidermal nevi, and skeletal or spinal abnormalities. Most children diagnosed with CLOVES do not have all of these signs, but rather a combination of abnormalities. Therefore, treatment of this condition varies greatly based upon what abnormalities are involved.


Last Updated 12/2013