Dilatation of the left kidney and ureter with cystic changes in the upper part of the ureter may be caused by left ureteral stone, left ureteral tumor, or pelvic tumor compressing the left ureter. 1. Left ureteral stone: left ureteral stone will block the ureter, resulting in obstruction of urine outflow channel, urine can not be discharged and stagnated in the ureter and kidney above the stone, resulting in hydronephrosis and ureteral effusion at the upper end of the stone, which will lead to dilatation of the left kidney and ureter with cystic changes in the upper part of the ureter. 2. Left ureteral tumor: left ureteral tumor and stone cause left kidney and ureter dilatation with upper ureter cystic changes in similar principle, also due to the urine can not be discharged stagnation in the ureter and kidneys. 3. Pelvic tumor compressing the left ureter: huge pelvic masses, such as ovarian tumor, fallopian tube tumor, aneurysm, etc., can compress and block the ureter from the outside of the ureter, resulting in ureteral stenosis, causing urine stasis, which leads to the left renal and ureteral dilatation with cystic changes of the upper part of the ureter. Therefore, there may be other reasons for left kidney and ureter dilatation with cystic changes in the upper part of the ureter, and it is recommended to actively consult a doctor under the guidance of a professional physician for diagnosis and treatment.