Nutcracker syndrome The left renal vein (LRV) converges into the inferior vena cava (IVC) on its journey and is compressed due to travel within the angle formed between the abdominal aorta (AO) and superior mesenteric artery (SMA), causing recurrent hematuria and proteinuria due to congenital or acquired morphological changes. Complications such as anemia and impaired renal function occur in a small number of patients. Anatomically, the AO forms a 45° to 60° angle between the AO and SMA, through which the LRV enters the inferior vena cava (IVC). The diagnosis is often clear when the ratio of the internal diameter of the dilated portion of the left renal vein to the stenotic portion is greater than or equal to 2 and greater than 3. In adolescence, the rapid growth in height, hyperextension of the vertebral body, and dramatic changes in body shape cause compression of the left renal vein between the angle of entrapment and obstruction of the return flow, resulting in dilatation of the left renal vein and an increase in its internal pressure. The left renal vein and its draining genital vein are stagnant, and abnormal traffic between the stagnant venous system and the urinary collection system occurs or non-glomerular hematuria is caused by rupture of the venous sinus wall of the calyx dome. The mechanism of upright proteinuria may be caused by a decrease in the angle between the abdominal aorta and the superior mesenteric artery due to visceral prolapse in the upright position, especially in the anterior spine position, which increases the pressure on the left renal vein. Clinical manifestations: It occurs from adolescence to about 40 years of age, and is more common in males. The onset of the disease in children is distributed between 4 and 7 years of age, with a high incidence in 13 to 16 years of age. The main symptoms of nutcracker phenomenon are asymptomatic upright hematuria or proteinuria, irregular menstrual bleeding, hypertension, occasional duodenal obstruction, or episodic or persistent carnal or microscopic hematuria; among them, asymptomatic carnal hematuria is more common; hematuria mostly appears in the evening or after exercise. The main manifestations are: 1. unilateral (left-sided) hematuria; 2. genital vein syndrome, i.e., testicular or ovarian vein stasis with dystocia, which is aggravated by standing or walking; 3. male varicocele. In addition, there are proteinuria, irregular menstrual bleeding, hypertension, etc. Treatment: 1. Conservative treatment: Applicable to most pediatric patients. Conservative treatment of microscopic hematuria, short interruption of meatus hematuria, only follow-up. The increase of fat and connective tissue at the angle between the superior mesenteric artery and the abdominal aorta, or the establishment of effective collateral circulation, allows the degree of compression of the left renal vein to be relieved, the stasis state to be improved and the symptoms to be relieved, and the hematuria to disappear. In most children, no medication is needed and the abnormal urinalysis is significantly improved after a period of observation. Measures: Absolute bed rest, anti-inflammatory, hemostasis, continuous bladder irrigation can be given when the bleeding is large, and the speed of irrigation is decided according to the amount of bleeding. 2.Surgical treatment: Treatment aim: to release the compression of the left renal vein. Indications for surgery: recurrent, severe, persistent hematuria, causing anemia, with renal impairment, not relieved by conservative, internal medicine treatment for more than 2 years. Surgical methods: superior mesenteric artery dissection and reanastomosis, left renal vein-inferior vena cava shunt. 3.Interventional treatment: left renal vein stenting, but this treatment has complications such as stent dislodgement or deformation, restenosis, thrombosis, etc. It is difficult to insert catheters and balloons when the left renal vein is severely stenosed, and it requires longer anticoagulation therapy and is expensive, so it is limited to individual case reports at present.