Arteriovenous Fistula
An arteriovenous fistula (AVF) is an abnormal direct connection between an artery and a vein, bypassing the normal capillary network. Some are intentionally created for dialysis access, while others develop from injury, prior medical procedures, congenital conditions, or as part of broader vascular malformations. Depending on size and location, AVFs can be asymptomatic, cause local symptoms, or strain the heart and circulation. Doppler ultrasound, CT angiography, and MR angiography are the central imaging tools for diagnosis, and treatment is individualized to the type, location, and impact of the fistula.
What is it?
In normal circulation, arteries carry oxygen-rich blood under high pressure away from the heart, then divide into smaller arterioles and finally into capillaries—tiny vessels where oxygen and nutrients are exchanged with the tissues. Blood is then returned through venules and veins back to the heart at lower pressure. An arteriovenous fistula is an abnormal direct connection between an artery and a vein that bypasses this capillary network, allowing high-pressure arterial blood to flow directly into a vein. Depending on the type, size, and location, this can have a wide range of effects—from no significant impact to important changes in tissue blood flow and heart workload.
Arteriovenous fistulas can be classified by how they develop. Some are intentionally created for medical purposes, particularly to provide reliable vascular access for hemodialysis in patients with advanced kidney disease (such as radiocephalic, brachiocephalic, or brachiobasilic AVFs). Acquired AVFs can result from trauma (including gunshot or stab wounds), medical procedures (such as catheter-based interventions, biopsies, or surgery), infections, certain cancers, or as a complication of arterial aneurysms. Congenital AVFs are present from birth and can occur in isolation or as part of broader vascular malformations or syndromes. Specific locations have their own characteristic forms—such as dural arteriovenous fistulas in the brain, pulmonary AVFs in the lungs (often associated with hereditary hemorrhagic telangiectasia), and renal or hepatic AVFs in those organs.
The clinical importance of an AVF depends on its size, location, and the patient’s overall health. Small AVFs may cause no symptoms and be discovered incidentally on imaging. Larger AVFs can produce a characteristic thrill (a buzzing sensation felt with the hand) and bruit (a whooshing sound heard with a stethoscope) at the site, along with local effects such as swelling, warmth, enlarged surface veins, skin discoloration, or pain. Some AVFs cause “steal syndrome,” in which blood is diverted away from downstream tissues, leading to pain, coldness, weakness, or, in severe cases, tissue damage in the affected area. Large AVFs increase the workload on the heart by returning a substantial amount of blood directly to the venous system at relatively high flow rates; this can contribute to high-output heart failure, particularly in patients with underlying heart disease or with very large or chronic fistulas.
Location-specific symptoms can be especially important. Dural AVFs (within the dural lining of the brain) may cause headaches, pulsatile tinnitus (rhythmic ringing in the ear), visual changes, or, less commonly, bleeding or neurological deficits. Pulmonary AVFs can produce shortness of breath, low oxygen levels, paradoxical embolic events (such as stroke from clots crossing through the fistula), or symptoms related to hereditary hemorrhagic telangiectasia. Renal AVFs may cause blood in the urine or high blood pressure, while AVFs in the gastrointestinal tract can lead to bleeding. Dialysis access fistulas may develop complications such as stenosis, thrombosis (clotting), aneurysmal enlargement, infection, steal syndrome, or central vein narrowing.
Diagnosis combines clinical examination with imaging. Doppler ultrasound is often the initial imaging test and provides useful information about flow characteristics, location, and size, particularly for peripheral and dialysis access AVFs. CT angiography provides detailed three-dimensional images and is especially useful for fistulas in the chest, abdomen, and brain, and for surgical or interventional planning. MR angiography is an alternative when avoiding radiation or iodinated contrast is preferred. Catheter-based angiography remains the standard for detailed characterization of complex AVFs and is typically performed at the time of planned intervention. Echocardiography, lung function testing, and other targeted studies may be added depending on the location and clinical impact.
Important to Know
Management of arteriovenous fistulas is highly individualized and depends on the type, location, size, and effects of the fistula, as well as the patient’s overall health. For many small or stable AVFs without significant effects, observation with periodic imaging is appropriate. For symptomatic, large, or high-risk fistulas, targeted treatment is generally needed.
Endovascular treatment with embolization—blocking the abnormal connection through catheter-based techniques using coils, plugs, glue, or particles—is now the most common approach for many acquired and congenital AVFs, including dural, pulmonary, renal, and visceral fistulas. Surgical repair is used in selected cases, particularly when endovascular treatment is not feasible or has been unsuccessful, and may include direct surgical closure, resection of involved tissue, or vascular reconstruction. Treatment decisions depend on anatomy, accessibility, associated conditions, and patient preferences.
Dialysis access AVFs require specialized care to maintain function and address complications. This includes regular monitoring for stenosis or thrombosis, endovascular procedures (such as angioplasty or thrombectomy) to maintain patency, and surgical revision when needed. Care is typically coordinated by nephrologists, vascular surgeons, and interventional radiologists or nephrologists with vascular access expertise.
Patients with pulmonary AVFs—particularly those with hereditary hemorrhagic telangiectasia—often benefit from screening and treatment with embolization to reduce the risk of paradoxical embolism and stroke. Patients with significant dural AVFs may require treatment to reduce the risk of bleeding, particularly when high-risk features are present.
High-output heart failure related to large AVFs may improve with treatment of the fistula. In the case of dialysis access AVFs causing significant cardiac strain, careful evaluation by a multidisciplinary team helps balance access needs with cardiovascular risk.
Care of complex or syndromic AVFs is typically delivered by multidisciplinary vascular anomaly teams that may include interventional radiology, vascular surgery, neurology and neurosurgery, pulmonology, nephrology, hematology, genetic counseling, and other specialists. Imaging findings are interpreted alongside symptoms, examination, and broader clinical context.
Patient education is important. Patients with known AVFs benefit from understanding the warning signs of complications and the importance of follow-up. Patients with hereditary hemorrhagic telangiectasia often benefit from systematic screening for AVFs in the lungs, brain, liver, and other organs, as well as from family screening and genetic counseling.
Red flag symptoms include sudden severe headache or new neurological symptoms (such as weakness, vision changes, or difficulty speaking), signs of stroke, sudden severe shortness of breath, sudden severe pain or swelling at the site of a known fistula, signs of infection (such as redness, warmth, fever), severe bleeding, sudden coolness or paleness of a limb, or signs of shock. These warrant prompt or urgent medical evaluation.