Arteriovenous fistula is a pathological direct communication between an artery and a vein (congenital or acquired) that creates blood flow bypassing the capillary network. It is localized on any part of the body or in internal organs (brain and spinal cord, kidneys, lungs, liver). Subcutaneous shunts look like expanded pulsating formations of purple color, disrupting local and systemic blood flow. Diagnosis is carried out by instrumental imaging methods (ultrasound and fistula angiography). Treatment includes endovascular embolization, microsurgical techniques and stereotactic radiosurgery.
I77.0 Arteriovenous acquired fistula
An arteriovenous fistula is a direct junction of an artery with a vein, passing blood, bypassing capillaries. This is a fairly rare disease – the frequency of pathological renal shunts does not exceed 1 case per 1000 people, spinal fistulas are even rarer (1 per 100 thousand). However, among vascular malformations of the brain, fistula formations account for 60-80%, the prevalence of peripheral variants reaches 20%. Pathological anastomoses of the femoral artery account for 12-30%, carotid and subclavian – up to 25% of the total number of such defects. Women suffer from arteriovenous dysplasia 2-3 times more often than men.
Causes of arteriovenous fistula
The occurrence of fistulas is mediated by damage to the arterial and venous walls under the influence of external or internal factors. Along with structural defects and diseases, iatrogenic factors are becoming increasingly important in the etiology of arteriovenous shunts. In vascular surgery , the following groups of causes are distinguished:
- Congenital anomalies. Most congenital malformations are the result of disorders of embryogenesis between 4 and 10 weeks of gestation. The effect of intrauterine infections, intoxication, arterial hypertension in the mother and taking certain medications during pregnancy is assumed.
- Hereditary diseases. The transformation of small vessels into arteriovenous shunts and aneurysms is observed in hereditary pathology – Randu-Osler-Weber disease (familial hemorrhagic telangiectasia), blue vesicular nevus syndrome. There is a link with gene mutations that disrupt normal angiogenesis (PTEN, RASA 1).
- Chronic pathology. The connection of pulmonal fistulas with chronic lung infections and parasitic invasions (tuberculosis, schistosomiasis, actinomycosis), thyroid cancer metastases was noted. Pathology occurs with cirrhosis of the liver and congenital heart defects.
- Mechanical injuries. The appearance of many acquired defects is associated with mechanical damage to veins and arteries located side by side and tightly adjacent to each other. This usually happens with stabbing, gunshot, less often blunt wounds, fractures of the base of the skull and long tubular bones with displacement of fragments.
- Invasive interventions. The probability of the appearance of pathological anastomoses increases with vascular catheterization (transfemoral aorto- and coronarography, percutaneous transhepatic cholangiography), biopsy of parenchymal organs (liver, kidneys). A similar problem is encountered after knee arthroplasty, intervertebral disc surgery, nephrostomy.
- Surgical manipulations. An artificially created junction between the arterial bed and the venous system is necessary for terminal renal failure to facilitate the hemodialysis procedure. Compared to other types of vascular access, the articular connection has a higher long-term patency with a good flow rate and a low risk of complications.
Erosions and spontaneous ruptures of arterial aneurysms into nearby veins play an important role in the etiopathogenesis of fistula anomalies. Significant and independent risk factors for pathological conditions are the use of anticoagulants (heparin, warfarin), hypertension, female sex.
The exact pathogenesis of primary arteriovenous malformations is unknown. An anomaly may occur in the terminal arterial loops, leading to the expansion of thin-walled capillary sacs. According to other assumptions, dysplasia results from incomplete resorption of the vascular septa separating the arterial and venous plexus in the intrauterine period of fetal development. It is assumed that small fistulas occur when capillary formation is disrupted.
Traumatic shunts are preceded by the formation of aneurysms and hematomas. Vascular fusion occurs according to the type of wound healing by primary tension. The blood that has poured into the surrounding tissues and partially dissipated is organized with the formation of a tubular passage that communicates the artery with the vein. The walls of the pathological shunt strengthen smooth muscle, connective tissue elements and endothelium, penetrating from the damaged branches. Constant blood flow through the fistula prevents its overgrowth.
Shunting of blood along pathological anastomoses provokes the theft of tissues located distally. When the pressure and characteristics of the blood flow change, turbulent flows occur on both sides of the defect, creating conditions for further damage to the vascular wall and degenerative processes. In peripheral tissues, the phenomena of arterial ischemia and venous hypertension are observed, a network of collaterals develops compensatorily. Large fistulas provoke an increase in the volume of circulating blood, a violation of cardiac activity, venous insufficiency.
Arteriovenous fistulas are part of the structure of vascular malformations. The isolated form (direct connection) accounts for 11% of cases, and a mixed shunt (with the presence of a tangle of altered branches) is characteristic of 53% of patients. In clinical angiology , such anastomoses are classified based on the following criteria:
- By origin. Primary fistulas are congenital, secondary fistulas are acquired. The latter are divided into traumatic, iatrogenic and spontaneous. Congenital always occur in isolation, without connection with other factors. Traumatic fistulas on the upper and lower extremities are equally common (20%), the proportion of intra-thoracic and intra-abdominal is about 4%.
- By localization. Based on the location, there are central (cerebral, spinal) and peripheral shunts (pulmonary, coronary, renal, hepatic, subcutaneous). In the area of the head and neck there are extracerebral (dural, carotid-cavernous anastomoses), intracerebral (pial), extracranial (main vessels of the neck), extra-intracranial (arterio-jugular) formations.
- By prevalence. Abnormal connections between arteries and veins can be limited and diffuse, single and multiple. Common forms have a clear genetic conditioning and can be included in the clinical structure of Cobb, Klippel-Trenone, Parks-Weber syndromes.
- By size. The gradation of arteriovenous fistulas by the size of the defect is one of the determining criteria influencing the choice of therapeutic tactics. Considering the diameter of the vein, there are several varieties of abnormal anastomoses: small (from 1 to 3 mm), medium (3-6 mm), large (more than 6 mm).
There is an angiographic classification of fistulas applicable to subcutaneous formations located in the trunk and extremities. Considering the morphology of the shunt, there are three types of lesions: I – arteriovenous, II – arteriovenous, III – arteriovenous.
Symptoms of arteriovenous fistula
The nature of the symptoms is determined by the localization of shunts and their size. Small formations on the extremities, in the lungs, kidneys and brain are usually asymptomatic and are an accidental diagnostic finding. Congenital pathology manifests itself in early childhood or at an older age. The clinical picture of posttraumatic fistulas develops immediately after injury or after several weeks, months.
Subcutaneous vascular fistula is noticeable by vein dilation, palpatory and visual pulsation, local swelling. Congenital processes are often accompanied by a change in skin color to red-purple. Above the fistula formation, the local temperature is elevated, signs of ischemia are observed in the distal parts: cold, pallor, dry skin. During auscultation, systolic and diastolic noise is heard above the pulsating anomaly. If you press the formation hard with your finger, then the heart rate slows down (Branham-Nicoladoni phenomenon).
A significant discharge of blood from the arterial to the venous bed with large fistulas leads to signs of hyperkinetic blood flow: tachycardia, increased systolic and pulse pressure, decreased exercise tolerance. Carotid-cavernous fistulas can manifest as pulsating exophthalmos, unilateral redness of the sclera and conjunctiva, double vision, decreased visual acuity, tinnitus. Cerebral malformations provoke the development of convulsive syndrome, headaches, neurological deficit phenomena (speech disorders, muscle weakness, coordination and sensory disorders, decreased memory and attention).
The initial symptoms of spinal formations are nonspecific, including difficulties climbing stairs, gait disorders, segmental sensory disorders (paresthesia, hypo-anesthesia), radicular pain in the extremities. Neurological symptoms gradually progress and have an ascending character. In the later stages, there are violations of urination, defecation, erection. Sometimes the disease has an acute onset and progressive development with intermediate remissions.
Long-term vascular shunts are accompanied by an increase in pressure in the diverting veins, which provokes their varicose veins with thrombosis and trophic disorders. The discharge of a large volume of blood past the capillaries leads to cardiac overload, cardiomegaly, the development of chronic circulatory insufficiency and endocarditis. Serious consequences of fistulas are associated with their rupture and the resulting internal bleeding.
The focus in the brain substance is complicated by hemorrhagic stroke with the development of persistent neurological disorders and disability of the patient. Renal abnormalities are accompanied by intraperitoneal and retroperitoneal bleeding, and rupture of the trunk trunks can have the most adverse consequences, up to a fatal outcome.
Diagnostics of arteriovenous fistula
Recognition of congenital and acquired arteriovenous fistulas in most cases is carried out by means of instrumental diagnostics. By clinical methods, it is possible to identify only a peripheral anomaly (on the trunk, extremities) or by a combination of symptoms to suspect its presence in any organ. Accurate visualization of vascular formation is provided by the following diagnostic procedures:
- Ultrasound scanning of fistulas. Duplex echography confirms the presence of arteriovenous messages on changes in blood flow parameters and vascular morphology. In the dilated bearing artery, the study demonstrates a flow with low resistance, at the level of the fistula it becomes turbulent and high-speed, and wide thick-walled veins are characterized by an arterialized waveform.
- CT angiography. Provides information about the anatomical features of the arteriovenous fistula. Depending on the location of the fistula, CT of peripheral arteries, examination of renal vessels, CT of the abdominal aorta are performed. Usually, computed tomography is performed with early contrast filling of the vein in the arterial phase. A detailed morphological analysis of the structures involved, an assessment of the location and size of the fistula are necessary to choose the optimal therapeutic strategy.
- MR angiography of malformation. Thanks to magnetic resonance angiography, it is possible to obtain optimal visualization of soft tissues, determining the relative location of affected and healthy structures. Most often, the study is carried out to identify abnormalities in the brain and spinal cord. The introduction of a contrast agent (based on gadolinium) makes it possible to evaluate hemodynamic parameters and increase the informative value of the method.
- Digital subtraction angiography. It is a contrast study of the vascular network with computer processing. Digital angiography is based on subtraction (subtraction) of the values of the tissue density of the template from other images, which makes it possible to distinguish the studied areas from the overall picture. First, an overview X-ray of the fistula defect is performed, all subsequent ones are performed with contrast enhancement.
- Traditional angiography of the mouth. It is prescribed immediately before the therapeutic correction or in situations when non-invasive imaging is not enough for a full diagnosis. Catheter angiography shows the flow dynamics with precise anatomy of veins and arteries, detecting the involvement of the smallest branches and collaterals. Peripheral arteriography of individual sites is usually performed.
The diagnostic program of arteriovenous fistula is compiled by a vascular surgeon or more specialized specialists. In addition to the described studies, CT or MRI of the head, spine, and internal organs are prescribed. Given the localization of pathology, it may be necessary to consult a neurosurgeon, pulmonologist, urologist and other doctors. The general pathology with which arteriovenous fistula should be differentiated includes similar malformations (capillary, plexiform), vascular aneurysms, hemangiomas, varicose veins.
Treatment of arteriovenous fistula
The purpose of treatment of arteriovenous fistula is to close the pathological junction while maintaining the patency of the main vessels. It is based on the principle of isolation and destruction of the abnormal connection of the arterial bed with the venous. The choice of optimal tactics is carried out taking into account the localization, size and type of the anastomosis, the dynamics of blood flow, and the features of the distal areas. In practice , several methods of defect correction are used:
- Endovascular embolization. It is the most common form of treatment for fistular malformations. It is based on the introduction of embolizing substances or devices into the central zone of the fistula: glue, particles or materials (Onyx, NBCA, STS), vascular plugs, spirals (stents), removable cylinders. Endovascular embolization is performed by catheterization of the femoral artery under X-ray control, shows high efficiency and minimal risk of recurrence.
- Microsurgery. The most suitable method of treatment of arteriovenous anastomoses of the brain and spinal cord is their removal independently or with endovascular embolization (clipping). With the help of neurosurgical access under a microscope, the pathological message is clamped with a titanium clip. Complete cessation of abnormal blood flow is confirmed by angiography.
- Stereotactic radiosurgery. It is advisable when the anomaly is localized in close proximity to functionally significant brain structures or in places that are difficult to access for other methods. It is carried out using linear accelerators and a gamma knife, with precise computer positioning and processing of the focus with a concentrated beam of radioactive radiation.
Abnormal shunts of small size that are not hemodynamically significant are subject to observation. Being a cosmetic defect, they can be removed by laser coagulation. Large subcutaneous fistulas require open surgical access with vascular reconstruction. For benign fistulas, conservative therapy is prescribed (compression knitwear, nonsteroidal anti-inflammatory drugs, angioprotectors). There is evidence of successful drug treatment of congenital arteriovenous dysplasia with metalloproteinase inhibitors and some immunosuppressants.
Prognosis and prevention
There are cases of spontaneous regression of primary arteriovenous fistulas. With long-lasting shunts, the risk of rupture and cardiac decompensation makes the prognosis unfavorable. But after radical correction, it is possible to completely get rid of the vascular defect, normalizing hemodynamics and restoring the function of the affected area. Measures for the prevention of acquired diseases include injury prevention, compliance with the technique of performing invasive interventions, timely treatment of chronic diseases. The risk of congenital malformations can be reduced by excluding negative effects on the fetus during pregnancy.