Strictly speaking, hydronephrosis cannot be considered an independent disease; it is merely a descriptive term in imaging, and is the result of many causes and various etiologies. It occurs because urine produced by the kidneys cannot smoothly pass through the ureters and bladder to be excreted from the body, leading to fluid accumulation in the renal pelvis and calyces. This may be caused by prostate enlargement, tumors in the urinary system, urinary system stones, or chronic inflammation and scarring of the ureters. Generally, hydronephrosis can be detected through imaging techniques, including urinary system ultrasound or CT, which can confirm the diagnosis.