Hydronephrosis does not necessarily cause severe pain. If the hydronephrosis develops suddenly over a short period, it might cause intense pain, most commonly due to urinary system stones blocking the ureter, leading to hydronephrosis. At this time, the ureter may experience spasms, causing severe pain. However, if the hydronephrosis develops gradually, the patient's pain symptoms might not be pronounced. For example, insufficient motility of the ureter or some type of narrowing could lead to the accumulation of fluid. If this condition develops slowly and persists for a long time, the patient might not feel particularly uncomfortable, despite the hydronephrosis, and it may only be discovered incidentally during a physical examination.