What is hydronephrosis? What are the risks of hydronephrosis to the human body? The normal human renal pelvis has a capacity of about 1-7 ml, usually 1 ml at the age of 1. If the pelvis is enlarged for various reasons it is called hydronephrosis. As a result of hydronephrosis, the pressure in the renal pelvis increases, compressing the surrounding renal parenchyma and causing atrophy and degeneration of the renal parenchyma, thus affecting the kidney function and causing kidney destruction. Due to the expansion and atrophy of the renal parenchyma, the normal growth and development of patients may also be affected. Moreover, due to the fluid accumulation, kidney stones and renal pelvis infections are easily induced, and in severe cases, sepsis may occur, endangering patients’ lives. What are the causes of hydronephrosis? Can it be prevented? Is there a high incidence of hydronephrosis? The vast majority of hydronephrosis is congenital and the causes include: 1) narrowing of the pelvic ureteral junction and high ureteral opening; 2) lack of/impaired peristaltic function of the pelvic ureteral opening; 3) pelvic ureteral junction valves; 4) extra-ureteral adhesion cords; 5) pelvic ureteral junction polyps; 6) vagal vascular compression of the pelvic ureteral junction. Prenatal testing can now detect hydronephrosis in the sixth month of pregnancy, and the incidence of hydronephrosis is about 1 in 500. How should a baby with hydronephrosis be seen and treated after birth? Once an intrauterine baby with hydronephrosis is identified, a prompt consultation with a pediatric urologist is indicated. Because hydronephrosis can be caused by many factors, some of which may lead to life-threatening conditions in affected children, prenatal evaluation should be performed. Postnatal ultrasonography should be repeated to confirm the diagnosis and treat as appropriate according to medical advice: 1. Many neonates with hydronephrosis are benign lesions, not true pelvic ureteral junction obstruction (less than 15%), which can be improved within 3 months; 2. Neonates with unilateral hydronephrosis have the possibility of self-improvement, with more than 80% maintaining more than 35% function, and hydronephrosis does not worsen and renal function does not continue to be impaired, which can be done without surgery; 3. Neonatal hydronephrosis should first be determined whether there is obstruction: sub-kidney function is greater than 40%/progressive improvement, the hydronephrosis is not aggravated by ultrasonography, the contralateral kidney does not have compensatory enlargement, and can be observed; 4. Neonatal bilateral hydronephrosis also has the possibility of self-improvement, and only 35% requires surgical treatment within 2 years. To what extent should hydronephrosis develop to be treated surgically? 1.In neonates without progressive renal impairment and worsening of hydronephrosis, surgical treatment is generally recommended after 3 months; 2.Significant obstruction symptoms: episodic abdominal pain, vomiting, abdominal mass; 3.Whole kidney/subrenal impairment: anterior and posterior pelvic diameter greater than 3 cm/subrenal function less than 40%; 4.Complicated urinary stones, infection, hypertension; 5.Progressive dilatation of renal pelvis; 6.Obstruction persists for 4-5 years. 5 years without improvement.