Mild hydronephrosis can be caused by the following reasons: First, physiological hydronephrosis, normal people will cause physiological hydronephrosis in the case of excessive bladder holding, this hydronephrosis will subside on its own and does not require special treatment. This type of hydronephrosis is often accompanied by renal colic, which can be clarified by ultrasound examination of the urinary tract. Third, hydronephrosis caused by ureteral stenosis or ureteral tumor needs to be clarified by further CT or MRI examination. Once this condition is found, further surgical treatment is needed.