Many parents of children who have an ultrasound result with “Nutcracker Phenomenon” often have the question: “My child has this problem at such a young age, is it serious? Will it get better in the future? Will there be more serious conditions? What should I do if it gets worse?” I understand parents’ feelings when I hear such questions, and I hope this article can clear up the confusion in their minds. Question 1: What is nutcracker phenomenon and nutcracker syndrome? A: First of all, it should be clear that nutcracker phenomenon and nutcracker syndrome are two different concepts. Nutcracker phenomenon, also known as left renal vein compression, refers to the compression of the left renal vein in the interstitial space between the abdominal aorta and the superior mesenteric artery or the abdominal aorta and the spine, often accompanied by a decrease in the blood flow velocity of the left renal vein and the expansion of the distal veins at the compression (see the figure below). When the nutcracker phenomenon causes a series of clinical symptoms such as hematuria, proteinuria and left lumbar and abdominal pain, it is called nutcracker syndrome. The report in the ultrasound will show the nutcracker phenomenon, and this phenomenon is usually considered a normal variant if there are no symptoms such as hematuria and proteinuria, so there is no need to worry too much. This condition requires regular review of the urinary routine and attention to whether the patient has symptoms related to nutcracker syndrome. Question 2: What are the prevalent groups and symptoms of Nutcracker syndrome? A: Nutcracker syndrome can occur at any age, especially in children and adolescents with rapid growth and development or in people with a slender body type. The common symptoms are hematuria (painless hematuria) and upright proteinuria. Upright proteinuria is mostly seen in young people, usually 24-hour urine protein is not greater than 1g, which can be reduced at rest and significantly aggravated after activity, left-sided back pain (with abnormal urinary routine) and gonadal vasodilation (left spermatic varicose veins). Question 3: What should be done after finding Nutcracker syndrome? A: Usually urine routine suggests occult blood or with left-sided low back pain. When Nutcracker syndrome is suspected, ultrasound is the test of choice to diagnose this disease. Most children and adolescents in the growth and development stage can heal themselves with age. Conservative treatment is preferred, avoiding strenuous exercise and exertion, applying symptomatic treatment, and coming to the hospital regularly to review urine routine, kidney function and left renal vein ultrasound. For those with more severe symptoms (including low back pain or abdominal pain, anemia, autonomic dysfunction, impaired renal function including persistent postural proteinuria and varicocele); adolescents after 2 years of conservative treatment and adults with poor results after more than 6 months of conservative treatment can consider surgical treatment (left renal vein transposition, left renal vein internal stenting and left renal vein external stent fixation). In conclusion: When the ultrasound suggests the phenomenon of nutcracker, don’t be too nervous first, you need to further improve the routine blood, urine and kidney function tests to see whether there is anemia, hematuria, proteinuria, abnormal kidney function, and also pay attention to whether there is abdominal pain and left-sided back pain symptoms. If none of these, then you do not need to worry, it means that you have anatomical abnormality of left renal vein compression, but it does not cause clinical symptoms, so you can review the relevant indexes regularly, and for growing adolescents this compression may be relieved with growth. If there are obvious symptoms, then it can be diagnosed as Nutcracker syndrome, which can be treated conservatively in mild cases and considered surgically in severe cases.