Varicoceles are a mass of veins in the scrotum that have become enlarged (varicose). The veins around the testicles drain blood from the testicles back to the heart. When blood pools in these veins (because the valves inside them aren't properly directing the blood), it can lead a sufficiently enlarged mass of veins that impairs fertility.

Sperm are most efficiently produced at a slightly lower than normal body temperature. The testes, where sperm are formed can maintain this lower temperature because they are located in the scrotum, which is outside the body cavity. When blood is prevented from properly flowing, the temperature in the testes rises. This adversely affects sperm production and quantity.

Up to 40% of men who are infertile have varicose veins around the testicles. We may recommend surgical treatment if it appears that a varicocele is present.