Varicoceles

A varicocele is an abnormal enlargement of the veins within the scrotum — the loose pouch of skin that holds the testicles. These veins are part of the venous drainage system that helps regulate testicular temperature and support healthy sperm production. When these veins become enlarged and dilated, similar to varicose veins in the legs, the condition is called a varicocele. It is one of the most common causes of male infertility, affecting up to 15% of men overall and as many as 40% of men with fertility issues.

A varicocele forms when the one-way valves inside the scrotal veins — which normally keep blood flowing upward from the testicles back to the heart — become weakened or fail to function properly. When these valves don’t close as they should, blood can flow backward and pool in the veins. Over time, this increased pressure causes the veins to stretch and enlarge.

The left testicle is more commonly affected because the left testicular vein drains into the left renal vein at a right angle, creating higher pressure compared to the right side, which drains directly into the inferior vena cava. This anatomical difference partly explains why most varicoceles occur on the left side — though they can develop on both sides.

As the veins enlarge, they disrupt the delicate temperature regulation system of the testicles. Because sperm production requires a temperature slightly lower than body temperature, this increased warmth can interfere with sperm quality, quantity, and motility — leading to reduced fertility in some men.