A varicocele is the swelling of the veins inside the scrotum. These veins are found along the cord that holds up a man’s testicles (spermatic cord).
A varicocele forms when valves inside the veins that run along the spermatic cord prevent blood from flowing properly.
Blood backs up, leading to swelling and widening of the veins. (This is similar to varicose veins in the legs.)
Most of the time, varicoceles develop slowly. They are more common in men ages 15 to 25 and are most often seen on the left side of the scrotum.
A varicocele in an older man that appears suddenly may be caused by a kidney tumor, which can block blood flow to a vein.