The processus vaginalis (or vaginal process) is an embryonic developmental outpouching of the peritoneum. It is present from around the 12th week of gestation, and commences as a peritoneal outpouching.
In males, it precedes the testis in their descent down within the gubernaculum, and closes. This closure (also called fusion) occurs at any point from a few weeks before birth, to a few weeks after birth. The remaining portion around the testes becomes the tunica vaginalis. If it does not close in females, it forms the canal of Nuck.
Failure of closure of the processus vaginalis leads to the propensity to develop a number of abnormalities. Peritoneal fluid can travel down a patent processus vaginalis leading to the formation of a hydrocele. Persistent patent processus vaginalis is more common on the right than the left. Accumulation of blood in a persistent processus vaginalis could result in a hematocele. There is the potential for an indirect inguinal hernia to develop, although not all people with a patent processus vaginalis will develop one. The more patent the processus vaginalis, the more likely the patient is to develop a hernia. Congenital malformation of the processus vaginalis is also the leading cause of testicular torsion, since lack of attachment to the inner lining of the scrotum leaves the testicles free to twist.