Congenital renal arterio venous malformations (RAVM) are clinically rare, with a prevalence of less than 0.04%. Patients have sudden, intractable hematuria as the main symptom, and in general, ultrasound, IVU, CT and MRI have no characteristic manifestations. Renal arteriography can make a clear diagnosis, while selective renal artery cannulation embolization is less invasive, more effective and can better preserve renal tissue, and has become the preferred treatment for congenital RAVM. From September 2001 to November 2009, 15 cases of congenital RAVM were treated with anhydrous ethanol embolization of the renal artery in our department, and satisfactory results were achieved, which are reported below. I. Pathology and clinical characteristics of congenital RAVM Congenital RAVM is an embryonic abnormality of vascular development, which is caused by the lack of capillary structure between the arteries and veins in the local kidney connected by a tortuous and dilated anomalous vascular network (nidus), and the arterial blood enters the veins directly through the anomalous vascular network. The anomalous blood vessels are often difficult to detect at birth due to their small size, but with growth and development or trauma and abnormalities in sex hormone levels, the hemodynamic changes occur in young and middle-aged people. According to the pathological anatomy and renal arteriography, congenital RAVM is divided into varicose veins and aneurysmal type. The varicose veins are relatively common, and the lesions are usually located in the submucosal lamina propria of the collecting system. The lesions often lack elastic fibers and are dilated in a bead-like or aneurysmal pattern, which can easily break into the collecting system and cause hematuria. Clinically, the first symptoms of 75% of varicose veins are hematuria of large bones, bladder congestion, back pain, etc. Hypertension is less common. Aneurysmal type is characterized by direct connection between the arteries and veins in the kidney by one or several larger anomalous vessels, and the fractional flow of aneurysmal type is much larger than that of varicose veins, which often leads to ischemia in the distal kidney tissue and increases renin secretion. The hematuria was less common than that of varicose veins. All 15 cases of congenital RAVM in this group were of varicose veins type, and they were seen with sudden and persistent hematuria, and none of them were combined with hypertension. The characteristic manifestation is the high-density vascular shadow located around the renal sinus and collecting system in the enhanced scan, with or without renal venous dilatation-9], and it can understand the renal function, which provides the basis for choosing the treatment plan and evaluating the treatment effect. MRI is also a good tool for the detection of such lesions; ultrasound is not easy to detect RAVM, but color Doppler or enhanced ultrasound can locally detect abnormalities in the blood flow signal, and it is important to confirm the diagnosis of such lesions, especially the smaller ones. Angiography is still considered to be the gold standard for confirming the diagnosis of these lesions, especially for the smaller lesions and their staging. Treatment of congenital RAVM In general, congenital RAVM requires clinical intervention, but very few vascular malformations can regress on their own. The cause of regression may be related to thrombosis caused by slowed blood flow or eddy flow in the malformed vessels after bleeding, hematoma compression and edema, etc., but close follow-up is still necessary. The main treatment methods for those who have failed conservative treatment are surgery and arterial embolization. Surgical procedures include nephrectomy or partial nephrectomy, which are complex and invasive, and may be complicated by medical RAVM. Percutaneous superselective arterial embolization is less invasive, with significant recent efficacy and low recurrence rate, and can preserve the normal kidney unit to the greatest extent, which is increasingly valued in the treatment of congenital RAVM. All 15 cases in this group have been followed up for a long time. None of the cases had recurrence of hematuria, and all cases had normal renal function. The key of embolization treatment for AVM is to permanently occlude the lesioned abnormal vascular mass, not its blood supply artery or drainage vein. The commonly used embolic agents such as spring ring, gelatin sponge and polyvinyl alcohol (PVA) pellets, because they block the proximal end of the blood supply artery, inevitably lead to reperfusion of collateral vessels and vascular neovascularization after the operation, and even aggravate the disease and lead to recurrence of hematuria. In this group of cases, there was also a patient who had 4 times of spring coil + PVA embolization before coming to our hospital, but the hematuria was aggravated and the imaging suggested that the lesion was enlarged. Due to its dehydrating and ablative effects, anhydrous ethanol denatures the contacting hemoglobin and directly destroys the endothelial cells of the malformed blood vessels of the lesion, providing a permanent embolization effect, thus achieving a cure for AVM. As a liquid embolic agent, ethanol is readily available, inexpensive, and can be adequately diffused within the abnormal vascular mass, and its metabolic clearance in vivo does not produce foreign body rejection, so ethanol is widely used as an embolic agent in AVM. To reduce the potential complications caused by intravascular injection of ethanol, the injection rate is recommended to be controlled at 0.2 ml/s, with 3 rnl per injection in the renal segmental artery and 2 ml in the interlobular artery. the embolic effect of anhydrous ethanol on malformed vessels is influenced by the arteriovenous fractional flow, and the embolic effect of anhydrous ethanol is reduced in cases with high fractional flow. In cases of high reflux, a spring-ring or balloon catheter can be used to block the flow. After 10-15 min of embolization of the lesion, a complete review of the angiogram should be routinely performed to avoid missing small vessels and newly opened side branches, and once found, complete embolization should be performed, but ectopic embolization caused by excessive embolization and regurgitation of the embolic agent should be avoided. For smaller lesions, a single embolization can often be completely eliminated, while for larger and complex lesions, multiple sequential treatments in stages are often required, with repeated treatment intervals of generally 2 months or more. The advantage of sequential treatment is that it can avoid potential complications caused by a large amount of anhydrous ethanol at one time, reduce the risk of excessive embolization at one time, and reduce complications such as tissue necrosis, rupture of aberrant vessels, or tissue edema after embolization. 25 patients embolized with anhydrous ethanol by Takebayashi et al. achieved complete occlusion of aberrant vessels in 17 cases and partial occlusion in 8 cases, with a follow-up of 5.1 to 13.2 years. There was no recurrence of hematuria. In 15 cases of varicose veins, 14 cases with slow shunts were cured once; in the other case, a larger arteriovenous fistula with extensive lesions was cured by two times of embolization with anhydrous ethanol combined with spring coil. There was no recurrence of hematuria at 4 to 96 months of follow-up. Although postoperative CT-enhanced scans showed disappearance of the malformed vessels in 8 cases, angiographic review was not performed, and it was uncertain whether the malformed vascular mass was completely occluded after surgery, which is worthy of continued observation in the future. V. Analysis of complications of renal artery embolization Our group of 15 cases and literature studies reported long-term follow-up proved the effectiveness of transarterial intervention for hematuria caused by RAVM. However, despite the use of superselective cannulation to the renal segmental artery or interlobular artery embolization, some degree of renal tissue infarction is inevitable. The post-embolization syndrome includes vague pain and fever in the renal region, which usually lasts for 5-7 d and requires no special treatment. Takebayashi et al. reported that in 30 cases of RAVM, the area of renal infarction ranged from 6.3% to 48.0%, with no effect on renal function. 8 cases in this group showed 5%-30% of renal embolism on CT review, with no decrease in renal function. Although no serious disease complications occurred in this group, during embolization and follow-up, we should be alert to the serious complications reported in the literature, such as renal hypertension caused by activation of renin-angiotensin system due to incomplete ischemia of renal tissues, formation of embolic agents in renal veins and inferior vena cava thrombosis after embolization, and pulmonary embolism or other ectopic embolism caused by granular embolic agents via shunts. Anhydrous ethanol embolization should be the treatment of choice to cure RAVM.