Nutcracker syndrome (NCS), also known as left renal vein entrapment syndrome or nutcracker phenomenon, is a condition in which the left renal vein is compressed through the angle formed by the abdominal aorta and the superior mesenteric artery (SMA) during its return to the inferior vena cava, causing hematuria, proteinuria, left lumbar and abdominal pain, and varicocele. This is a less commonly recognized condition that causes hematuria, proteinuria, left lower back pain, and varicocele. The clinical manifestations are mainly asymptomatic hematuria or microscopic hematuria, and some of them may present with renal varices, varicocele, proteinuria, hypertension and low back pain. In recent years, with the improvement of diagnostic techniques, the incidence of NCP-induced hematuria is on the rise, and it is especially common in children (33.13%), but the incidence is not high in adults, and it is easily misdiagnosed and missed. Anatomically, the left kidney is located close to the abdominal aorta (AO) and the right kidney is located close to the inferior vena cava (IVC), so the left renal vein (LRV) is longer than the right renal vein (RRV) and the right renal vein injects directly into the IVC, whereas the left renal vein needs to cross the angle between the abdominal aorta and its branch superior mesenteric artery (SMA) to inject into the IVC (Figure 1). Normally this angle is 45° to 60° and is filled by mesenteric fat, lymphoid tissue and peritoneum so that it does not compress the LRV, but when the angle decreases (<30°), clinical phenomena of LRV compression can occur in conditions such as faster pubertal development, rapid height growth, spinal hyperextension, rapid changes in body shape or renal prolapse, upright or supine position, enlarged lymph nodes and tumor compression (i.e. "Nutcracker Phenomenon"). Nutcracker phenomenon often has three clinical consequences: (1) compression of the left renal vein causes bruising of the left renal venous system, where the bruised venous blood undergoes abnormal traffic between the venous sinus and the terminal end of the renal calyx or rupture of part of the venous wall, resulting in unilateral hematuria of the left kidney (non-glomerular hematuria); (2) genital vein syndrome, where abdominal pain is caused by bruising of the kuccal or ovarian veins that drain into the LRV and is aggravated by walking or standing: (3) Varicocele in men (LRV branch). Clinical manifestations occur in males from adolescence to about 40 years of age, with childhood onset distributed between 4 and 7 years of age, and a high incidence seen in males and females between 13 and 16 years of age. Asymptomatic episodes of carnal hematuria may be observed, or submicroscopic hematuria may be detected by urinalysis on routine physical examination, and may be aggravated by strenuous exercise or upright position, sometimes accompanied by left abdominal pain or lumbago. Some patients also have hematuria with proteinuria, which ranges from trace to 2+ and can manifest intermittent or postural exacerbations. In addition, varicocele can occur in men, and in women, irregular menstrual bleeding, etc.