Patients with hydronephrosis do not all experience pain. In fact, only a minority of patients experience pain. Hydronephrosis is caused by some form of urinary obstruction, such as urinary system stones, tumors, or problems like prostate enlargement, which prevent urine from being excreted smoothly. In this case, the accumulation of fluid can be a long-term, gradual buildup. Patients often adapt to the progression of the condition and do not exhibit obvious symptoms, especially in the early stages. However, some patients may experience pain, such as those with urinary system stones, or pain may occur when a tumor ruptures.