Arteriovenous fistulas are hollow tubular tubes formed in the body as a result of injuries or pathological processes.
Arteriovenous fistulas are connections between veins and arteries. As a result of the appearance of fistulas, blood from the veins begins to flow directly into the arteries, while in the normal mode of functioning of the human body, blood from the heart must go through the arteries into the capillary system and from there, through the veins, return to the heart.
Arteriovenous fistulas and aneurysms are severe defects of the vascular system. Untimely or poor treatment leads the patient to serious complications (such as decompensation of cardiac activity), disability and often death at a fairly young age!
Why are arteriovenous fistulas dangerous?
The appearance of arteriovenous fistulas or fistulas leads to a deterioration in the blood supply to important areas and organs of the human body. Arterial pressure also falls, while the pressure in the veins rises. The load on the heart increases, which at the same time it begins to experience a lack of blood flow due to a violation of the blood circulation cycle.
All this can lead to various, including severe cardiovascular diseases, aneurysms – an increased load of blood flow on the veins can lead to their stretching and rupture – and thrombosis, which can develop in the areas of veins below the site of the fistula.
Another type of complications caused by arteriovenous fistulas are cosmetic defects: spots on the skin and tissue edema.
Signs and symptoms
The symptoms of dural arteriovenous fistulas (dural AVF) can vary widely depending on the location of the fistulas. Some fistulas are asymptomatic and not detectable until patients are examined for other neurological or vascular diseases.
Some of the common symptoms of dural AVF include:
- Headaches – Headaches are one of the most common symptoms with all types of dural arteriovenous fistulas;
- Ringing in the ears – An unusual ringing or buzzing in the ears can be symptomatic, especially when the fistula is near the ear. Some patients hear a pulsating murmur caused by blood flow through the fistula.
- Stroke-like symptoms – All types of dural arteriovenous fistulas can cause symptoms like them and seizures if they rupture. Bleeding in the brain is the most serious side effect and can lead to permanent disability or death.
- Vision problems. When a fistula is located near the eye, patients often complain of visual impairment, redness of the eyes, and swelling and congestion of the sinus.
Diagnosis and treatment
Arteriovenous fistulas are diagnosed using modern ultrasound examinations (Doppler, ultrasound scanning), computed tomography and magnetic resonance imaging. If the fistulas are deep, doctors may resort to contrast X-ray angiography.
Treatment of arteriovenous fistulas is surgical.
Small congenital fistulas can be removed with laser coagulation. Also, congenital and acquired arteriovenous fistulas can be removed by endovascular methods, when a certain substance is injected into the vessel under the influence of X-rays, which blocks the direct communication between the vein and the artery.
In more complex cases, surgery is performed to remove the fistula.
Early diagnosis is of great importance in the treatment of vascular diseases.
Causes of dural AVF
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 play an increasingly important role in the etiology of arteriovenous shunts. In vascular surgery, the following groups of reasons are distinguished:
- Congenital anomalies. Most congenital malformations result from abnormalities in embryogenesis between 4 and 10 weeks of gestation. The defect can be caused by intrauterine infections, intoxication, arterial hypertension in the mother and taking certain medications during pregnancy;
- 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 bladder nevus” syndrome. There is a connection with gene mutations that disrupt normal angiogenesis;
- Chronic pathology. The connection of pulmonary fistulas with chronic pulmonary infections and parasitic invasions (tuberculosis, schistosomiasis, actinomycosis), metastases of thyroid cancer was noted. Pathology occurs in cirrhosis of the liver and congenital heart defects;
- Mechanical injury. The appearance of many acquired defects is associated with mechanical damage to the vein and artery, 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 dis-placement of fragments;
- Invasive interventions. The likelihood of pathological anastomoses increases with vascular catheterization (transfemoral aorta- and coronary angiography, percutaneous transhepatic cholangiography), a biopsy of parenchymal organs (liver, kidneys). A similar problem is encountered after knee arthroplasty, intervertebral disc surgery, and nephrostomy;
- Surgical manipulations. An artificially created anastomosis be-tween the arterial bed and the venous system is necessary for end-stage renal failure to facilitate the hemodialysis procedure. Compared to other types of vascular access, the artificial junction has higher long-term patency with a good flow rate and a low risk of complications.
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 enlarged bringing artery, the study demonstrates a low-resistance flow, 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. It provides information about the anatomical features of an arteriovenous fistula. Depending on the location of the fistula, CT of the peripheral arteries, examination of the renal vessels, and 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 involved structures, an assessment of the location and size of the fistula is necessary to select the optimal therapeutic strategy;
- MR-angiography of malformation. Thanks to magnetic resonance angiography, it is possible to get optimal visualization of soft tissues, determining the relative position of the affected and healthy structures. Most often, research 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 assess the hemodynamic parameters and increase the information content of the method;
- Digital subtraction angiography. It is a contrast study of the vascular network with computer processing. Digital angiography is based on the subtraction of the density values of the template tissues from other images, which makes it possible to isolate the studied areas from the general picture. First, a survey X-ray im-age of the fistular defect is performed, all subsequent ones are performed with contrast enhancement;
- Traditional anastomosis angiography. It is prescribed immediately before medical correction or in situations where non-invasive imaging is not enough for a full diagnosis. Catheter angiography shows flow dynamics with the precise anatomy of the veins and arteries, revealing the involvement of the smallest branches and collaterals. Peripheral arteriography of specific areas is usu-ally performed.
The diagnostic program is drawn up by a vascular surgeon or more narrow specialists. In addition to the studies described, CT or MRI of the head, spine, internal organs is prescribed.
Given the localization of the pathology, it may be necessary to consult a neurosurgeon, pulmonologist, urologist and other doctors.
The goal of treatment is to close the pathological anastomosis 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 one. The choice of optimal tactics is carried out taking into account the localization, size and type of anastomosis, dynamics of blood flow, and 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 fistula malformations. It is based on the introduction of embolizing substances or devices into the central zone of the fistula: glue, particles or materials, vascular plugs, spirals (stents), removable balloons. Endovascular embolization is performed by catheterization of the thigh artery under X-ray control, shows high efficiency and minimal risk of recurrence;
- Microsurgery. The most suitable method for treating arteriovenous anastomoses of the brain and spinal cord is their removal on their own or with endovascular embolization (clip-ping). With the help of neurosurgical access under a microscope, the pathological message is clamped with a titanium clamp (clip). Complete cessation of abnormal blood flow is confirmed by angiography;
- Stereotactic radiosurgery. It is advisable when localizing an anomaly in close proximity to functionally significant structures of the brain 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 treatment of the focus with a concentrated beam of radioactive radiation.
Small abnormal shunts that are not hemodynamically significant should be monitored. 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 indicated (compression hosiery, non-steroidal anti-inflammatory drugs, angioprotectors).
There is evidence of successful drug treatment of congenital arteriovenous dysplasias with metalloproteinase inhibitors and some immunosuppressants.
There are cases of spontaneous regression of primary arteriovenous fistulas. With long-term shunts, the risk of rupture and cardiac decompensation makes the prognosis unfavorable.
But radical correction makes it possible to completely get rid of the vascular defect, normalize hemodynamics and restore the function of the affected area.
Prevention measures for acquired anastomosis include injury prevention, adherence to the technique of performing invasive interventions, and timely treatment of chronic diseases. The risk of congenital malformations can be reduced by eliminating a negative effect on the fetus during pregnancy.
Prevention of congenital arteriovenous fistulas has not yet been developed. To prevent the formation of acquired fistulas, timely and adequate treatment of injuries and careful hemostasis during surgical interventions are required.