Varicocele is common on left testis because
Variocele formation has been attributed to one of the three primary factors : Increased venous pressure in left renal vein Collateral venous anastomoses Absent or incompetent valves in the internal spermatic vein. Ref : Bailey & Love 23/e p1273
Left testicular vein drains into IVC which has high pressure
Left testicular vein drains into left renal vein which has high pressure
Left testis is lower situated
Compression of testicular vein by rectum
Urology