An 8mm separation of the left renal collecting system is not normal. It may be due to physiologic factors such as holding urine, or it may be due to stones or ureteral obstruction, but it is usually not serious. Physiological factors: the patient has had previous urinary stones causing hydronephrosis, which may also suggest the presence of renal collecting system separation on ultrasound imaging; when the patient performed renal ultrasound, the holding of urine was more obvious, which may also lead to the separation of the collecting system, so it does not necessarily have a pathological significance. Attention to regular review. Pathological factors: renal collecting system separation, need to consider the possibility of urinary tract obstruction below the ureter. For example: urinary stones, urinary tumors, urinary tract infections, malformations and so on. When separation of the left renal collecting system is found to exist, it is necessary to exclude the presence of renal stones, ureteral stones and other problems, and it is recommended to consult the urology department of a regular hospital for diagnosis.