During the 3rd month of gestation, the testis begins its descent from a retroperitoneal location, through the inguinal canal until the scrotum. An extension of the peritoneum - a transparent membrane which lines the abdominal cavity and covers the abdominal organs - called the processus vaginalis in males and the canal of Nuck in females is the remnant of this descent. It is obliterated in 95-98% of term infants.
A hydrocele is the result of a patent processus vaginalis that allows peritoneal fluid to travel into the scrotum.
Differently from inguinal hernias, the hydrocele and the cyst of the spermatic cord can heal spontaneously during the first year of life. Usually, they do not present complications. The surgical correction of the hydrocele, regardless of the size, is recommended after 18 months old when still there is clinical evidence of an open processus vaginalis. As the child grows up and starts playing in physical activities that require more effort, the hydrocele can increase the size and become symptomatic.