What is an arteriovenous fistula? The arteries in the body are the conduits that carry blood to the tissues and organs. The oxygen-rich arterial blood passes through the capillaries of the tissues for metabolism and delivery of nutrients to the tissues, and the metabolized blood then flows back to the heart through the veins. Therefore under normal conditions there can be no direct traffic between arteries and veins and it has to pass through a large number of capillaries, where the pressure in the veins is significantly lower and the oxygen content is significantly lower. If there is a direct traffic between arteries and veins, a “short circuit” is formed and arterial blood enters veins directly without passing through capillaries (or the original capillaries are thickened and blood passes through them significantly faster), an arteriovenous fistula is formed. Theoretically, arteriovenous fistulas can occur in all tissues and organs of the body. It can occur in the extremities or in the internal organs. However, the disease is more common in the extremities, so I will focus here on arteriovenous fistulas of the extremities. How are arteriovenous fistulas of the extremities classified? What are the characteristics of each? There are various ways to classify arteriovenous fistulas, but they are generally classified as congenital or acquired, depending on the course of the disease. Congenital arteriovenous fistulas are vascular malformations, while acquired arteriovenous fistulas are most often caused by trauma. The difference between congenital and acquired arteriovenous fistulas is that the fistula is small and extensive, and the lesion often involves several tissues, such as skin, subcutaneous, muscle and bone; it causes systemic hemodynamic changes, but rarely leads to heart failure. Congenital arteriovenous fistulas usually develop in childhood or during adolescence, but there are cases where symptoms become apparent only in adulthood. Diffuse vascular hyperplasia and limb hypoplasia are common: the lesion is often located in one limb, the upper limb lesion may extend to the shoulder and chest, the lower limb lesion may extend to the waist and hip, the superficial veins are widely dilated, often manifesting as lateral varicose veins or forming spongy hemangiomas, the local temperature is elevated, the blood flow is increased due to the presence of extensive arteriovenous anastomosing branches around the deep tissues and bones, and the blood oxygen is increased, prompting the affected limb to Thickening and growth of the affected limb. Patients feel heavy, swollen and painful limbs. It is often accompanied by wine stains (flaky skin erythema) and is medically known as Klipple-Trenaunay syndrome (KT syndrome) or vascular malformation bone hypertrophy syndrome. In cases of multiple fistulas or large fistulae, localized scattered murmurs and tremors may be present. In severe and prolonged varicose veins, stasis nutritional changes, including hyperpigmentation, eczema, and ulcer formation, may occur. Arteriovenous fistulas that divert local arterial blood to the veins are in fact a form of blood theft and can cause ischemic changes in the distal tissues, coldness at the ends of the fingers (toes), and even ulceration or gangrene. The later onset of the disease is mostly limited to the hands and feet and is characterized by proximal venous dilatation and high pressure distal limb ischemia. 2. Acquired arteriovenous fistulas are mostly due to trauma or other causes of abnormal traffic between arteries and veins. The most common ones are caused by penetrating injuries, such as gunshot wounds and stab wounds, and in a few cases, they can also be caused by blunt injuries, such as fracture breaks or kidney contusions, which also damage the corresponding arteries and veins. There are also some medical injuries, such as arterial puncture or cannulation. The clinical presentation of acquired arteriovenous fistulas varies depending on the size, location, and duration of the fistula. In larger arteriovenous fistulas, the shunting of high pressure arterial blood through the fistula to low pressure veins results in a significant and persistent tremor at the site of the fistula and a machine-like murmur on auscultation that increases during cardiac systole. The larger the fistula, the louder the murmur and the more pronounced the tremor. The arterial pulsations distal to the fistula are mostly diminished or absent. The arterial blood flowing into the veins causes venous hypertension and consequent dilatation of the superficial veins. The distal side of the foot or hand may suffer from nutritional deficiencies due to reduced arterial blood supply and venous stasis, and even toe or finger necrosis due to ischemia. The skin temperature is significantly higher on the proximal side of the arteriovenous fistula and lower on the distal side. In addition, a large amount of arterial blood passing directly through the fistula into the vein can lead to heart failure when there is a large increase in return blood. The thicker the diameter of the fistula and the closer it is to the heart, the earlier heart failure occurs. How are arteriovenous fistulas diagnosed? Arteriovenous fistulas of the extremities have specific symptoms that are obvious and can be initially diagnosed by a specialist. However, a definitive diagnosis requires further testing. The most reliable tests are angiography, CT angiography (CTA) and magnetic resonance angiography (MRA), which provide a panoramic view of the arteries and veins and can be performed from different angles, and have a reliable diagnostic value, especially in cases of acquired arteriovenous fistulas with a single fistula. It is also valuable for congenital arteriovenous fistulas, but may have false positive results. Dynamic arteriovenous cannulography under fluoroscopy is the most reliable and is useful to clarify the location and extent of the fistula. Sometimes a venogram is also required. What is the treatment of arteriovenous fistula? There are surgical, interventional, and compression therapies. Many experts believe that the treatment of congenital arteriovenous fistula begins with embolization or surgery and ends with amputation. This indicates that the treatment of this disease is more difficult. However, in the face of the pain suffered by the patient, the doctor still has to take active measures according to the situation in order to reduce the pain and protect the function as much as possible. 1, surgical treatment: in the past, there was an arteriovenous fistula resection, but now it is less used. Congenital arteriovenous fistulas are extensive and the fistula opening is small, so it is difficult to achieve complete removal except for limited lesions. 2, interventional therapy: more often used intra-arterial embolization method. Under the supervision of X-ray and TV screen, the artery is cannulated to the main branch vessels near the arteriovenous fistula and embolic substances such as spring ring, gelatin sponge, silicone spheres, autologous muscle or autologous blood clot or other polymeric preparations are injected to embolize part of the arteriovenous fistula to relieve the symptoms or to prepare the lesion for resection thereafter. In cases of extensive lesions, multiple arterial injections may be performed, and sometimes local injection of embolic agents into the diseased artery under fluoroscopy may be considered. These methods may cause ischemia or gangrene of the extremity. In cases of an abnormal increase in arterial branching, overlapping stents may also be used to block the abnormal branches from within the artery. Sclerotherapy can also be used: a small number of injections of sodium cod liver oil or anhydrous alcohol into the tissue between the arteriovenous fistula or within the fistula. Compression therapy: local compression bandages or medical compression stockings are a basic protective measure, both before and after treatment. Acquired arteriovenous fistulas can often be treated with overlapping stents, while congenital arteriovenous fistulas require a combination of treatments. In congenital arteriovenous fistulas, we mainly use a combination of narrowing of the proximal trunk artery, ligation of the anomalous arterial branches and interventional treatment to reduce flow and accelerate reflux in order to reduce venous pressure in the limb, with satisfactory recent results.