Renal pelvis dilatation is common in clinical practice and usually refers to hydronephrosis caused by the presence of a urinary tract obstruction. If the obstruction is simple upper urinary tract obstruction, it often causes dilatation of one renal pelvis. In the case of bilateral hydronephrosis, it usually causes dilatation of the renal pelvis on both sides. In general, upper urinary tract obstruction is a common cause of unilateral pelvic dilatation, and the main causes include ureteral stenosis, ureteral calculi, and so on. For bilateral hydronephrosis, it is usually caused by lower urinary tract obstruction, such as common prostatic hyperplasia, urethral stricture and female bladder neck sclerosis, which are all common causes of bilateral hydronephrosis. The treatment for pyel dilation and hydronephrosis generally requires the removal of the obstruction. Only by removing the obstruction from the urinary tract can the hydronephrosis be relieved, thus allowing the pyel dilation to recover.