What are arteriovenous malformations (AVMs)?  

AVMs  are abnormal connections between arteries and  veins that are congenital (present at birth). They don't have  the normal intervening capillary bed, the network  of tiny vessels (capillaries) that normally connect  arteries and veins. AVMs are more common  in the brain than in other regions. 

What causes AVMs? 

For most  AVMs precise cause(s)  are unknown. They are  believed to be caused by a mistake  in the formation  of the normal arterial-capillary-venous connections that occurs during early embryonic life. No known food, medication,  or activity during pregnancy can cause  an AVM. 

Some AVMs appear  in a familial disorder called hereditary hemorrhagic telangiectasia (HHT) (Rendu-Osler-Weber syndrome). The two genes that cause HHT  are known; both  result in the loss of function  in cell receptors. The condition usually presents with telangiectasia  of the skin and mucous membranes (mouth and gastrointestinal tract). The telangiectasia bleed, typically during puberty. In HHT,  AVMs also occur in  the lungs, liver, and brain. Another genetic condition is called capillary malformation-  AVM. Multiple, usually oval capillary stains occur  in a family;  an AVM is present in about 10 percent  of family members  the causative gene is RA5AI- it  also is involved  in some patients with Parkes Weber syndrome. 

What are the chances  a child would have AVMs? 

What are  the symptoms of AVMs?

AVMs develop before 5  to 6 weeks  of embryonic life. Usually  an AVM  is seen as  an innocent vascular stain  at birth;  often they begin to enlarge  in childhood  and adolescence. Intracranial (within  the head) AVMs are silent and present slowly  or suddenly in adults. 

Intracranial AVMs  often present with headache  or other neurologic signs or  with sudden  bleeding into the brain.  AVMs outside  the brain present more slowly with color changes, then ulceration/bleeding  of the skin,  and persistent pain. In time, if  the blood flow through  an AVM is excessive,  the heart can  become overworked. 

AVMs can occur in any organ in  the body, in order  of frequency: head, limbs, trunk,  and internal organs. 

In infancy  and childhood,  the blush  of an  AVM can be mistaken  for hemangioma (the most common tumor  of infancy). AVM becomes obvious as signs  of fast  blood flow appear.  The skin becomes a darker red  or purple color, nearby veins enlarge a mass appears beneath  the stain,  and there is local warmth. 

What problems  are associated with AVMs? 

Hereditary hemorrhagic telangiectasia (HHT)  is a fairly common familiar vascular disorder  that presents with tiny little capillaries  on the skin  and mucus membranes, three causative genes  are known patients with HHT  can develop  AVMs in  the lungs, brain,  and gastrointestinal track. 

Parkes Weber syndrome involves diffuse AVM of  a limb with overgrowth  of that limb.  The affected limb usually has CM involving  some of the skin, and is increased  in length and girth. When  the amount  of blood passing through  the AVM is very large,  the heart is affected because it has  to handle more  blood flow (high-output cardiac failure). Our research collaborators have identified  a gene (RA5AI)  that is changed in about one half  of the patients with this syndrome (CM_AVM). 

Wyburn-Mason syndrome, also called Bonnet-Dechaume-Blanc syndrome,  is a rare vascular malformation  of the central nervous system. It is the association  of a vascular anomaly  in the retina  and a cerebral AVM, sometimes accompanied  by a facial capillary stain and/or overgrowth on one side  of the body. 

Cobb syndrome  is an association  of a CM  of the skin with  an underlying AVM  of the spinal cord  as well as the adjacent muscular  and bony elements  of the spine. 

When should a child be referred  to a specialist? 

A specialist should  be contacted whenever an AVM is suspected. 

How  are AVMs diagnosed?

On physical examination,  the overlying skin is warm and,  in time, the pulsation  of blood flow can be felt. The shunting  of blood through an AVM can be detected earlier by ultrasonography. 

Magnetic resonance imaging (MRI)  is the best diagnostic examination and gives  the most information about  the extent  of the anomaly. The  most precise study is angiography,  in which  a contrast dye that can be seen by X-ray fluoroscopy  is injected into  the AVM via  a flexible tube called a super selective  catheter that is usually inserted  in the groin. 

How are AVMs treated?

Some intracranial  AVMs are controlled by proton-beam irradiation, while others  can be treated by  embolization (injection  of material into  the center  of the anomaly via  a catheter) and/or  surgical excision.  In other parts  of the body, AVM  is often treated either by  embolization or sclerotherapy (direct injection  of an irritating solution). Whenever possible, surgical resection gives  the best chance for  a "cure." 

What  is the long-term outlook for  a child with  an AVM? 

What research is being done  on AVMs? 

Investigators hope  to learn more about AVMs by  studying the normal development  of arteries, capillaries,  and veins during  the embryonic period. By understanding  the molecular signaling involved  in the formation and growth of these  vascular channels, it is hoped  that defective messages can  be interpreted.