Hydronephrosis can potentially cause patients to exhibit symptoms of edema. Urine is produced by the kidneys and is expelled from the body through the urinary system, including the ureters and bladder. If there is an obstructive issue in the urinary system, the urine produced by the kidneys cannot be excreted smoothly, leading to hydronephrosis. When a large amount of fluid cannot be excreted, it eventually causes edema in the body. However, if the patient has hydronephrosis on only one side and the other kidney is healthy, the healthy kidney can fully compensate for the entire kidney function and sufficiently excrete fluids. Therefore, patients with unilateral hydronephrosis often do not show obvious signs of edema. But if a patient has bilateral hydronephrosis, and urine produced by both kidneys cannot be excreted, the patient will exhibit signs of edema.