During development, testicles descend down a tube from the abdomen into the scrotum. Hydroceles result when the tube fails to close and fluid drained from the abdomen through the open tube accumulates in the scrotum, where it becomes trapped, causing the scrotum to swell. It may also be caused by inflammation or trauma of the testicle or epididymis, or by fluid or blood obstruction within the spermatic cord. Hydroceles caused by trauma or blood obstruction are more common in older men.
Attribution: Straight Talk Foundation