A varicocele often produces no signs or symptoms. Rarely, it might cause pain. The pain may:

• Vary from sharp to dull discomfort
• Increase with standing or physical exertion, especially over long periods
• Worsen over the course of a day
• Be relieved when you lie on your back
• Impaired fertility

With time, varicoceles might enlarge and become more noticeable. A varicocele has been described as looking like a "bag of worms." The condition might cause a swollen testicle, almost always on the left side.

Your spermatic cord carries blood to and from your testicles. It's not certain what causes varicoceles.

However, many experts believe a varicocele forms when the valves inside the veins in the cord prevent your blood from flowing properly. The resulting backup causes the veins to widen (dilate). This might cause damage to the testicle and result in worsened fertility.

Varicoceles often form during puberty. Varicoceles usually occur on the left side, most likely because of the position of the left testicular vein.

There don't appear to be any significant risk factors for developing a varicocele.

A varicocele might cause:

• Shrinkage of the affected testicle (atrophy). The bulk of the testicle comprises sperm-producing tubules. When damaged, as from varicocele, the testicle shrinks and softens. It's not clear what causes the testicle to shrink, but the malfunctioning valves allow blood to pool in the veins, which can result in increased pressure in the veins and exposure to toxins in the blood that may cause testicular damage.
• Infertility. Varicoceles might keep the local temperature in or around the testicle too high, affecting sperm formation, movement (motility) and function.