Arteriovenous Fistulas 

Updated: Nov 10, 2017
Author: Sateesh C Babu, MD; Chief Editor: Vincent Lopez Rowe, MD 

Overview

Background

Vascular birthmarks encompass a group of vascular disorders that for a long time included conditions of various presentation and etiology. In 1996, the Workshop of the International Society for the Study of Vascular Anomalies (ISSVA) presented a new classification of this vast group of conditions, which divided them into vascular tumors and vascular malformations.[1, 2] This allowed more systematic classification and management with less confusion in diagnosis of these often complex lesions. The ISSVA classification of vascular anomalies has subsequently been modified and refined.[3]

Arteriovenous fistula (AVF), by definition, describes an abnormal communication between an artery and a vein. These communications are congenital; can occur at any point in the vascular system; and vary in size, length, location, and number. AVF is a term reserved for a singular communication between an artery and a vein that usually has an acquired etiology.

The first recorded case of an arteriovenous malformation (AVM) was in the late 16th century. In 1757, Hunter described an AVF as an abnormal communication between an artery and a vein. Krause in 1862 used injection studies of an amputated specimen to characterize the abnormal vasculature. In 1875, Nicoladoni described the reflex slowing of the pulse following occlusion of an artery proximal to an AVM.

In 1920, Halsted contended that an AVM could produce cardiac enlargement and observed that a congenital AVF without a nevus is rare. In 1936, Holman described the pathophysiology and natural history of AVMs; this publication forms the basis for today's knowledge. In 1967, Fontaine observed that puberty or pregnancy can cause enlargement of AVMs.

Promising advances are being made in the diagnosis and treatment of AVMs. These advances provide hope to patients who are affected by this sometimes debilitating disease.

Pathophysiology

In the classification of vascular anomalies currently employed, a division is made between tumors and malformations.[3] The first group is characterized by high turnover of endothelium, whereas the latter is characterized by the presence of dysmorphogenesis with no evidence of abnormal epithelial turnover.

Vascular tumors

The most common vascular tumor is infantile hemangioma. It is seen shortly after birth, is more common in girls and in whites, and is congenital. These tumors are usually solitary but not infrequently they may be multiple and involve the liver, gastrointestinal (GI) tract, and central nervous system (CNS). They are characterized by three phases of growth, as follows[4] :

  • Proliferation
  • Involution
  • Involuted phase

The first phase is characterized by rapid growth of the tumor, bright red or bluish in color, firm, and tense in appearance. They may develop surface ulcerations and episodes of bleeding.

The involuting phase usually begins at the end of first year of life and is characterized by decreased tempo of the tumor growth, with the gradual color fading from the center of the mass and less tense consistency.

Transition to the involuted phase occurs during the second half of the first decade of life. Normal skin is restored in half of patients, and persistent skin changes such as telangiectasias, skin thinning and scarring may occur.

Other congenital tumors include tufted angioma, congenital hemangioma, and kaposiform hemangioepithelioma.[3]

Vascular malformations

Generally, congenital vascular malformations are inborn errors in embryologic development. Woollard described the development of the vascular system in three stages, as follows:

  • The first step is the condensation of undifferentiated cells into capillary blood spaces
  • The next stage involves the formation of a retiform plexus in which blood flows from an arterial to a venous side; the channels in the retiform plexus combine and regress to form the vessels in the vascular system
  • The last stage involves the development of axial arteries in the limb buds

The final product is a complex interplay among genetic, hormonal, biochemical, and chemical factors. Developmental arrest can occur at any point during vessel formation, creating different types of vascular malformations. The exact cause for the arrest is not entirely known. All AVMs are present at birth, but they are not always clinically evident. Stimuli during puberty or pregnancy or following minor trauma can precipitate clinical features of the malformation.

Vascular malformations are characterized by normal epithelial turnover and are usually sporadic; however, some of them have been linked to genetic disorders. They can be subdivided according to the type and size of vascular bed involved, as well as the rate of flow through them.

Capillary malformations

Capillary malformations are usually sporadic; they can be divided into slow-flowing Klippel-Trenaunay, Maffucci, and Proteus syndromes and fast-flowing Parkes Weber and Bannayan-Riley-Ruvalcaba syndromes. These malformations are frequently associated with dilated capillary vessels in the dermis, asymmetric overgrowth of the involved limbs, and sometimes multiple soft tissue tumors, abnormal development of venous and arterial systems, and the presence of port-wine stains (see the image below).

Buttock port-wine stain. Buttock port-wine stain.

Lymphatic malformations

Lymphatic malformations are usually related to genomic mutations and include Milroy disease, Meige syndrome, yellow-nail syndrome, and Noonan syndrome. They are usually characterized by abnormal development of different portions of the lymphatic system.

Venous malformations

Venous malformations are the most common vascular malformations. They are usually sporadic and may be present at birth but are not always clinically obvious and predominantly occur in the skin and soft tissue (see Presentation). They include glomuvenous malformation and blue rubber bleb nevus syndrome.

Arteriovenous malformations

AVMs have the presence of arteriovenous shunts in multiple capillary beds both on the skin and involving internal organs. They are usually accompanied by a bruit and hyperemia with prominent venous outflow (see Presentation). They are represented by hereditary hemorrhagic telangiectasia syndrome, also known as Rendu-Osler-Weber disease.

Although the pathogenetic mechanisms of AVMs are not completely understood, the hemodynamic alterations that lead to the clinical manifestations of AVMs have been described well.

An abnormal communication causes shunting of blood from the high-pressure arterial side to the low-pressure venous side. This creates an abnormal low-resistance circuit that steals from the high-resistance normal capillary bed (see the image below).

Hypertrophied subclavian artery resulting from low Hypertrophied subclavian artery resulting from low-resistance high-volume flow through an upper extremity arteriovenous malformation (AVM).

Blood follows the path of least resistance. Flow in the afferent artery and efferent vein increases, causing dilatation, thickening, and tortuosity of the vessels. If the resistance in the fistula is low enough, the fistulous tract steals from the distal arterial supply, actually causing a reversal of arterial flow in the segment distal to the AVF. This is known as a parasitic circulation. The parasitic circulation causes decreased arterial pressures in the distal capillary beds and can cause tissue ischemia.

The increased flow into the venous circulation does not necessarily cause higher venous pressures. However, it can cause vessel wall abnormalities, such as thickening of the media and fibrosis of the wall. These changes are known as arterialization.

The blood flow into the venous circulation causes turbulence, which is responsible for the palpable thrill. The thrill is dependent on the geometry of the fistula and does not represent volume of flow accurately.

In addition to the decreased distal arterial pressures, which might cause distal ischemia, peripheral venous pressures are increased, leading to swelling, visible veins (varicosities), and even ulcers in the limb.

The heart responds to the decreased peripheral vascular resistance by increasing stroke volume and cardiac output. This leads to tachycardia, left ventricular dilatation, and, eventually, heart failure.

Mulliken has described a system of classifying AVMs on the basis of structural criteria, as follows:

  • Truncal AVMs - These are usually hemodynamically active and tend to present in the upper limb, head and neck, and pelvis; the lesions are localized and composed of a mass of enlarged vessels
  • Diffuse AVMs - These are usually found in the limbs, more frequently in the lower limbs than the upper limbs; in contrast to the truncal type, the connections are small and numerous; they are hemodynamically less active
  • Localized AVMs - These are usually inconsequential hemodynamically because of higher resistance in the connections; the lesions are composed mainly of abnormal intercalated tissues, not masses of enlarged vessels

Any structural type of AVM can be hemodynamically active or stable.

Etiology

The majority of AVMs are developmental errors that occur between weeks 4 and 10 of embryogenesis. The factors that cause these errors are unknown. Potential exogenous causes, such as viral infections, toxins, and drugs, have been implicated but not yet proven. Almost all AVMs are sporadic and nonfamilial, though a few syndromes (eg, Sturge-Weber, Klippel-Trenaunay) include inherited vascular abnormalities.

The most common etiology for acquired AVFs is penetrating trauma. AVFs also can occur from nontraumatic causes, such as erosion of an aneurysm into a neighboring vein or following surgery for therapeutic purposes (eg, access for hemodialysis).[5]

Epidemiology

All AVMs are present at birth, but they are not always clinically evident. Stimuli during puberty or pregnancy or following minor trauma can precipitate clinical features of the malformation.[6]  AVMs occur with equal frequency among males and females.

Prognosis

Many congenital AVMs/AVFs may regress spontaneously. The large ones, over the years, may lead to cardiac decompensation and death. In acquired AVFs, death can occur from cardiac failure, infection (bacterial endocarditis), or rupture if the AVF is between a large artery and vein (like iliac or renal AVFs or aortocaval fistulas); however, the prognosis is excellent once the AVF is corrected.

Yakes et al obtained follow-up studies in 19 of 20 patients with AVMs treated with ethanol embolization.[7] All patients showed persistent occlusion of the malformation radiographically after as long as 24 months of follow-up.

Widlus et al treated 11 patients with cyanoacrylate embolization. During a 40-month follow-up period, 82% reported complete resolution of their symptoms and the remaining patients showed improvement. No patients reported worsening of their symptoms with embolization in these 2 series.[8]

Do et al treated 12 patients for pelvic AVMs with combined endovascular and embolosclerotherapy. During the medial follow-up period of 33.2 months, 10 showed no residual lesion and complete symptomatic relief; 2 experienced partial remission.[9]

Pearce reported experience in 15 patients with vascular malformations treated surgically. Five patients were lost to follow-up. Assuming that those patients did well and did not seek further intervention, two thirds of those undergoing excision improved; 13% were unchanged after surgical excision, and 20% were worse.

Prompt recognition is important for outcome. Brinjikji et al reviewed spinal dural AVFs (lesions that are commonly missed on imaging or misdiagnosed) diagnosed at their institution between January 1, 2000, and November 1, 2014.[10] They found that delays in diagnosing these AVFs led to a high incidence of additional disability that frequently could not be reversed by surgical or endovascular treatment.

Patient Education

Physicians must be aware of the subtle signs of AVF in order to make the correct diagnosis. Prominent veins in the leg in a young individual following trauma, which may be mistakenly diagnosed as simple varicose veins, and rapid onset of heart failure in an otherwise healthy person, which may be diagnosed as cardiomyopathy, are examples for the need to look further for the presence of AVFs.

 

Presentation

History

Cutaneous malformations can present with a mass, pink stain, dilated veins, unequal limb length and girth, or skin ulceration. (See the image below.)

Buttock port-wine stain. Buttock port-wine stain.

Patients may experience limb heaviness that is aggravated with dependency and relieved with elevation. One half of patients experience pain. The pain may be caused by tissue ischemia or by mass effect on local nerves. Some lesions, such as glomuvenous malformations, can be tender to palpation.[11]

The increased blood flow to the limb in congenital arteriovenous malformation (AVM) or arteriovenous fistula (AVF) may result in increased growth of the limb (ie, one leg may be larger and longer than the other). In acquired AVFs, a history of trauma (eg, gunshot wound, stab wound, or even blunt trauma and fractures) can exist. AVF can also occur after medical diagnostic or interventional procedures (eg, angiography) or even after operative procedures that have caused inadvertent trauma to the artery and vein.

Physical Examination

Small AVFs and AVMs may be totally asymptomatic and may be discovered incidentally. Large AVFs may present with increased size of the limb, mild discoloration, swelling, or prominent veins with audible murmur or palpable thrill. (See the images below.)

Lower extremity venous malformation. Lower extremity venous malformation.
Upper extremity arteriovenous malformation (AVM). Upper extremity arteriovenous malformation (AVM).

The lesion may be pulsatile. The Branham sign may be present (slowing of the heart rate upon compression proximal to the AVM). Patients may develop hyperhidrosis, hypertrichosis, hyperthermia, or a palpable thrill or bruit over the lesion. They may have functional impairment of limbs or joints from mass effect or gangrene from prolonged tissue ischemia. Visceral AVMs can present with hematuria, hematemesis, hemoptysis, or melena.

Rarely, patients present initially with signs of congestive heart failure (eg, dyspnea, leg edema). This is particularly common when the communication is between a very large artery and a vein.

Complications

Except for very small AVFs, all acquired AVFs must be treated to prevent complications of distal limb ischemia, continued large flow of blood with eventual heart failure, and rarely infection (eg, endocarditis). Recurrence is a complication of inadequate or incomplete treatment.

 

DDx

Diagnostic Considerations

Differential diagnosis of arteriovenous fistula (AVF) includes other conditions that may cause hyperdynamic circulation (increased heart rate, increased cardiac output, and low peripheral resistance). Cirrhosis, hyperthyroidism, Paget disease of the bone, and, occasionally, vary large highly vascular tumors like sarcomas should be considered.

Missing the presence of AVF after blunt or penetrating trauma is easy, but this condition should always be looked for in this setting. In cases of any gunshot wound or stab wound that traverses the course of a blood vessel, ruling out vascular injury, particularly AVF, with an imaging study (duplex ultrasonography, computed tomography, magnetic resonance angiography, or even conventional angiography) is important. Failure to diagnose may have medicolegal implications.

Differential Diagnoses

 

Workup

Laboratory Studies

Blood gas analysis in an arteriovenous fistula (AVF) reveals a higher oxygen saturation in the venous blood immediately distal to the fistula as compared with normal venous blood.

Hemodynamic assessment with flow directed balloon catheter (Swan-Ganz catheter) reveals high cardiac output and low peripheral vascular resistance (PVR).

Extremely large AVFs or arteriovenous malformations (AVMs) may present with low platelet count (due to turbulence and trapping of platelets), and occasionally, with laboratory findings of consumptive coagulopathy, such as low platelets, elevated prothrombin time (PT) and partial thromboplastin time (PTT), increased bleeding time, low fibrinogen, and elevated euglobulin clot lysis time (signs of fibrinolysis).

Imaging Studies

Plain films may demonstrate soft tissue masses or abnormalities within bony structures.

Duplex ultrasonography is usually the initial study to delineate the extent and flow characteristics of the malformation. Doppler ultrasonography can be used preoperatively and intraoperatively, but it does not have any therapeutic use. Duplex scans will show reversal of flow in the artery distal to the AVF, the steal phenomenon, or proximal flow augmentation in mixed arteriovenous malformations.

Contrast-enhanced computed tomography (CT) is useful to locate the abnormality, to evaluate for aneurysm formation, and to identify bony involvement. A retrospective review by Biswas et al found four-dimensional CT angiography (CTA) to be accurate in characterizing AVMs and dural AVFs, yielding findings that agreed well with those of digital subtraction angiography.[12]

Magnetic resonance imaging (MRI) is the criterion standard in the preoperative evaluation of patients with arteriovenous malformations (AVMs). MRI generates multiplanar views and can be used to accurately define tissue planes and to identify critical flow characteristics. It is the best modality to define local soft-tissue and adjacent organ involvement, which helps with preintervention planning. Magnetic resonance sequences can be postprocessed into magnetic resonance angiography (MRA) images (see the image below), which help define the malformation more clearly.[13, 14]

Hand angiogram demonstrating arteriovenous connect Hand angiogram demonstrating arteriovenous connections. Note the steal of blood from the fingertips.

Contrast angiography is the most important method for investigating AVMs or AVFs while also affording the capability for therapeutic interventions. It is an excellent method of delineating the number, location, and extent of the arteriovenous connections. Angiographic signs include early filling of veins, hypertrophied and tortuous arteries proximal to the malformation, and varicose and dilated veins distal to the fistula.

Radiolabeled studies can determine the shunt fraction, which is the proportion of blood being shunted through the fistulous tract.

Other Tests

Plethysmography is useful for quantifying flow in a whole limb, but assessing blood flow through circumscribed areas is difficult. Ideally, plethysmography data are compared with normal data from the contralateral limb.

Thermography determines heat loss from a region. However, results are of limited clinical value because they do not reveal the location of the lesion accurately, and the data cannot be used to differentiate among various types of vascular malformations.

In AVFs involving limbs, segmental limb pressure measurements can document a significant drop in pressure distal to the fistula. This can be used before and after surgical correction of the fistula to confirm that the fistula has been eliminated.

Procedures

Percutaneous biopsy is never indicated in the workup of a known vascular malformation; bleeding that is difficult to control may result. Biopsy should be performed if the suspected lesion is solid and falls into the category of vascular tumors.

Invasive and noninvasive cardiac evaluation may be indicated in patients with congestive heart failure because cardiac output can be markedly elevated in patients with large proximal AVMs. Cardiac output is best measured with invasive right-heart catheter techniques but can be evaluated noninvasively with echocardiography. In order to document success, measurement of cardiac output is indicated before and after surgical or interventional procedures to reduce the size of these larger AVMs.

Histologic Findings

Histology documents arterialization of the thickening of the wall of the vein, including its muscular layer, and thinning of the artery in large, long-standing AVFs.

 

Treatment

Medical Care

Most vascular tumors can be observed through their typical phases of development until they involute. Children should be evaluated for the extent of the tumors and involvement of vital structures. Lesions in endangering locations are best treated with corticosteroids (injected intralesionally or administered systemically), interferon alfa, laser ablation, and embolization therapy.[15, 16]

Most arteriovenous malformations (AVMs) can be medically managed and controlled; only a few demonstrate progressive growth and warrant surgical intervention. Most of the symptoms of AVMs (pain, heaviness, swelling) are due to venous hypertension. The cornerstone approach in managing lower-extremity symptoms is elastic support hose. An elastic support stocking that provides 30-40 mm Hg of compression is usually sufficient to relieve leg symptoms.

Alcohol sclerotherapy may shrink the size of the AVM, but this treatment also places the patient at risk for peripheral nerve injury. The treatment of large AVMs with alcohol must be performed by an experienced interventional radiologist, and these risks must be explained to patients when they consent to undergo therapy.

Various newer treatments (eg, photodynamic therapy, antiangiogenic therapy, and new methods of sclerotherapy) are available that may offer options worth considering.[17]

Surgical Care

Indications for surgical intervention of vascular malformations include the following:

  • Hemorrhage
  • Painful ischemia
  • Congestive heart failure
  • Nonhealing ulcers
  • Functional impairment
  • Limb-length inequality

Transcatheter embolization of vascular malformations became an extremely valuable option in the treatment of these frequently complex and deeply seeded anomalies.[18] This modality can be effectively applied alone, prior to, or in combination with surgical resection when the vascularity of the malformation must be reduced.

The procedure involves the percutaneous placement of a vascular catheter and the injection of coils or particulate matter into the malformation. Passage of emboli into the normal circulation occurs but usually only poses a problem if it enters the cerebral or mesenteric vasculatures.[19, 20] The procedure is especially useful in the treatment of AVMs.

The common adverse effects are pain and tenderness near the malformation and a transient fever and leukocytosis. More worrisome complications include necrosis of healthy adjacent tissue and neurologic injury. Thorough angiographic imaging and clear delineation of the vessels helps minimize most of these adverse effects. Embolization can provide a promising treatment option if it is carried out by an experienced interventional radiologist.

In the treatment of venous malformations, a number of sclerosing agents, including absolute ethanol injections, can be implemented. They can carry a risk of necrosis of adjacent tissue and should be used with caution.[21]

Most AVMs are not amenable to complete surgical excision. A lesion must be well localized for a chance at complete resection. Resectability depends on the degree of extension into adjacent structures. Patients with disease that extends into the deep fascia or contiguous structures (eg, muscle and bone) usually are not surgical candidates. Malformations that extend into the pelvis and gluteal region also are not surgically resectable. Those patients severely afflicted with malformations who are not candidates for local extirpation may be candidates for amputation and rehabilitation with a limb prosthesis.

In contrast to congenital AVMs, which are difficult to treat, almost all acquired arteriovenous fistulas (AVFs) are amenable to either surgical or interventional treatment. Occlusion of the feeding vessel with coils can be done. If the AVF is between a medium-sized or large artery and a vein, then occlusion of the artery may be hazardous. Surgical treatment is preferred. The fistulous communication is disconnected, and repair of the defect in the artery and vein is accomplished.

Some of these problems can be addressed with minimally invasive endovascular techniques.[22, 23] A covered stent graft is deployed in the artery, thus covering the site of communication between the artery and vein.