Why do you have hydronephrosis and what causes it? Hydrocele is a relatively common disease that can accompany people throughout their lives. Simply put, any factor that affects the urine produced by the kidneys and its smooth discharge from the body may be the cause of hydrocele. There are many causes of hydronephrosis, and clinically it is commonly used to classify patients with hydronephrosis into two categories: congenital acquired hydronephrosis and acquired secondary hydronephrosis. This kind of hydronephrosis is “innate”, mostly caused by some congenital malformations of the urinary tract, including pelvic ureteral junction stenosis, ureteral bladder junction stenosis, vesicoureteral reflux, etc. There are also congenital anatomical abnormalities such as horseshoe kidney, duplicated kidney, and posterior urethral valve disease. There are also acquired secondary hydronephrosis, which includes urinary tract infections, stones, injuries, exogenous compression of the urinary tract, tumors and some benign growths, which cause urinary tract obstruction and thus hydronephrosis. In addition to this classification, fluid can also be classified according to the location of the hydronephrosis: upper urinary tract factor and lower urinary tract factor. The degree of obstruction can be classified as complete or incomplete hydrops. According to the nature of the effusion, it can be divided into, mechanical and dynamic effusion. It is worth noting that the disease spectrum of causes of hydrocele, is changing over time. Initially, congenital factors accounted for a significant proportion of the causes of hydronephrosis, while nowadays, hydronephrosis caused by urinary stones, upper urinary tract injuries, malignant tumors, etc., are on the rise.