A hydrocele testis is an accumulation of clear fluid within the cavum vaginale, the potential space between the layers of the tunica vaginalis of the testicle.

A primary hydrocele testis causes a painless enlargement in the scrotum on the affected side and is thought to be due to the defective absorption of fluid secreted between the two layers of the tunica vaginalis (investing membrane).

The accumulation can be a marker of physical trauma, infection, tumor or varicocele surgery,[1] but the cause is generally unknown.

It has also been found to decrease a man's sex drive and make him less active for fear of enlarging the mass.

Congenital hydrocele testis results when the processus vaginalis remains, allowing fluid from the peritoneum to accumulate in the scrotum.

[3] Sclerotherapy, the injection of a solution following aspiration of the hydrocele fluid may increase success rates.