Arteriovenous malformation (AVM) is an abnormal connection between veins and arteries, usually congenital.
AVMs can occur in various parts of the body:
- Brain, causing a cerebral arteriovenous malformation
- Spinal cord
- Intercostal space
- Spermatic cord
Some arteriovenous malformations can be associated with genetic abnormalities. Any patients with an unusual arteriovenous malformation or with signs of these syndromes should be evaluated by a genetics counselor.
Mutations in the PTEN gene can cause Bannayan-Riley-Ruvalcaba and Cowden Syndrome. Vascular malformations in these disorders most commonly are intra-muscular with extensive amounts of fat.
RASA1 mutations are associated with a rare condition called Parkes-Weber Syndrome. This is a Capillary Malformation – Arteriovenous Malformation (CM-AVM), which causes significant overgrowth usually of an extremity. There may also be a lymphatic component.
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 can 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 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 (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.
Intracranial (brain) lesions often cause headaches or other neurologic signs. They can also suddenly bleed into the brain. Lesions in other parts of the body may lead to ulceration, bleeding and persistent pain. If the blood flow through an arteriovenous malformation is excessive, the heart will enlarge over time, and this may result in a type of heart failure.
Treatment and mangagement of arteriovenous malformations include:
- Observation. Small asymptomatic lesions are sometimes just observed over time without intervention.
- Embolization. Embolization is the injection of material into the center of the lesion to block the blood supply of the lesion. There are several different agents that Inteventional Radiologists can use for 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.
- Surgical excision (removal). This approach alone is more likely to be successful with localized lesions. When combined with preoperative embolization (injection of material into the center of the lesion to block the blood supply of the lesion, thereby reducing bleeding during surgery), it offers the best chance for cure. If the core of the lesion is completely removed, the lesion will not recur. When the location and extent of the arteriovenous malformation make removal of the entire core of the lesion impossible, the lesion may recur.
- Some intracranial arteriovenous malformations are treated by protein-beam irradiation while others are treated with embolization or surgical care.
Hereditary Hemorrhagic Telangiectasia (HHT)
A genetic disorder called hereditary hemorrhagic telangiectasia (HHT) or Rendu-Osler-Weber syndrome is characterized by multiple, small arteriovenous lesions that can occur in the:
- Mucous membranes (mouth, nose, and gastrointestinal tract)
- Other sites
Two genes are known to cause this condition, both 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 nosebleed, laser treatment of the nasal septum (thin membrane between nostrils) can be quite helpful.
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 magnetic resonance angiography (a specific type of MRI that looks at the flow of blood in vessels) 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.