A varicocele is the enlargement and twisting of veins in the scrotum. These veins become dilated due to improper functioning of valves that regulate blood flow. Normally, these valves ensure that blood flows in one direction—back toward the heart. When they fail, blood pools in the veins, causing them to expand.

Varicoceles are more common on the left side of the scrotum due to anatomical differences in how the left testicular vein connects to the renal vein.

Although it is not always dangerous, varicocele can affect testicular function, hormone levels, and sperm production over time.