Common causes of varicocele include: 1. Abnormal venous valves: The venous valves in the spermatic vein help prevent the backflow of blood. If these valves are abnormal, it can lead to blood reflux, causing varicocele. 2. Higher incidence of varicocele on the left side: Varicoceles are more likely to occur on the left side because the left spermatic vein enters the left renal vein at a right angle. Moreover, the left renal vein is often compressed by the superior mesenteric artery and the abdominal aorta, leading to obstructed blood flow in the spermatic vein. 3. Other secondary pathological changes, such as retroperitoneal tumors, renal tumors compressing the veins in the spermatic cord, or tumor thrombus embolizing the renal vein, can also cause obstruction in the spermatic venous flow, leading to varicocele.