It is the remnant of a pouch of peritoneum which is pulled into the scrotum by the testis as it descends out of the abdominal cavity during foetal development.

[5] The volume of the fluid in the cavity may increase abnormally when lymphatic drainage is impeded (due to inflammation, neoplasm, or trauma).

[5] The tunica vaginalis is derived from the vaginal process of the peritoneum, which in the fetus precedes the descent of the testes from the abdomen into the scrotum.

[7] The vaginal process between the abdominal inguinal ring and the superior part of the testis is then obliterated, usually leaving a string-like or cord-like remnant adjacent to the spermatic cord.

[2] If the vaginal process fails to obliterate, the communication between the peritoneal cavity and scrotum persists after birth, predisposing the individual to indirect inguinal hernia, and hydrocele testis.