A hydrocele is a fluid-filled sack along the spermatic cord within the scrotum.

Hydroceles are common in newborn infants.

During normal development, the testicles descend down a tube from the abdomen into the scrotum. Hydroceles result when this tube fails to close. Fluid drains from the abdomen through the open tube. The fluid builds up in the scrotum, where it becomes trapped. This causes the scrotum to become swollen.

Hydroceles normally go away a few months after birth, but their appearance may worry new parents. Occasionally, a hydrocele may be associated with an inguinal hernia.

Hydroceles may also be caused by inflammation or injury of the testicle or epididymis, or by fluid or blood blockage within the spermatic cord. This type of hydrocele is more common in older men.

The main symptom is a painless, swollen testicle , which feels like a water balloon. A hydrocele may occur on one or both sides.

During a physical exam, the doctor usually finds an swollen scrotum that is not tender. Often, the testicle cannot be felt because of the surrounding fluid. The size of the fluid-filled sack can sometimes be increased and decreased by pressure to the abdomen or the scrotum.

If the size of the fluid collection varies, it is more likely to be associated with an inguinal hernia.

Hydroceles can be easily demonstrated by shining a flashlight (transillumination) through the enlarged portion of the scrotum. If the scrotum is full of clear fluid, as in a hydrocele, the scrotum will light up.

An ultrasound may be done to confirm the diagnosis.