Varicoceles are veins that become enlarged inside the scrotum of men – comparable to developing a varicose vein in a leg.  The scrotum is a sac that holds the testicles and is part of the male reproductive system that makes, stores, and moves sperm.  The testicles make sperm and the hormone testosterone.  Sperm that are in the process of maturing will move through the epididymis, a coiled tube behind each testicle.