Left kidney effusion 23mm belongs to mild hydrocele, the specific causes, generally consider that there may be pregnancy factors, renal tumors and ureteral stones, etc., the specific causes need to be further analyzed. 1. Pregnancy factor: during pregnancy, with the continuous growth and development of the fetus, the size of the uterus will increase, resulting in the left ureter being compressed, causing the ureter to be occluded, which induces mild left hydronephrosis. 2. Kidney tumor: the appearance of left kidney tumor will lead to the normal structure and function of the left kidney being damaged, causing mild hydronephrosis and other symptoms. 3. Ureteral hydronephrosis: the presence of stones in the left ureter will lead to mild left hydronephrosis induced by ureteral blockage. It is recommended that patients with left hydronephrosis go to regular hospitals to receive further examination, clarify the cause of the disease, and follow the doctor’s instructions for standardized treatment.