Many causes of varicoceles have been offered. The valves in the veins may not work well (or may be missing). If blood flow is sluggish, blood may pool in the veins. Also, the larger veins moving from the testicles towards the heart are connected differently on the left and right side. So more pressure is needed on the left side to keep blood flowing through the veins towards the heart. If blood flows backwards or pools in the veins, that can cause them to swell. Rarely, swollen lymph nodes or other abnormal masses behind the abdomen block blood flow. This can lead to sudden swelling of the scrotal veins. This is often painful.
Are Varicoceles Common?
About 15 out of 100 men have varicoceles. It's hard to predict which of these 15 will have fertility problems caused by their varicocele. But about 4 in every 10 men tested for fertility problems have a varicocele and decreased sperm movement. There's no link with other defects, race, place of birth, or ethnic group. Although varicoceles are often found in men tested for infertility, 8 out of 10 men who have a varicocele don't have fertility problems.