A varicocele (VAR-ih-koe-seel) is an enlargement of the veins within the loose bag of skin that holds your testicles (scrotum). A varicocele is similar to a varicose vein you might see in your leg.
Varicoceles are a common cause of low sperm production and decreased sperm quality, which can cause infertility. However, not all varicoceles affect sperm production. Varicoceles can also cause testicles to fail to develop normally or shrink.
Most varicoceles develop over time. Fortunately, most varicoceles are easy to diagnose and many don't need treatment. If a varicocele causes symptoms, it often can be repaired surgically.