The tunica vaginalis is a pouch of[2]serous membrane[3] within the scrotum that lines the testis and epididymis (visceral layer of tunica vaginalis), and the inner surface of the scrotum (parietal layer of tunica vaginalis). It is the outermost of the three layers that constitute the capsule of the testis, with the Tunica albuginea of testis situated beneath it.
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.[3]
Anatomy
Visceral layer
The visceral layer of tunica vaginalis of testis (lamina visceralis tunicae vaginalis testis)[4] is the portion of the tunica vaginalis that covers the testis and epididymis. It is the superficial-most of the three layers that constitute the capsule of the testis, with the tunica albuginea of testis situated deep to it. Posteriorly, the visceral layer does not line the surface of the testis - instead, it passes onto the epididymis where the latter attaches to the testis before continuing onto the inner surface of the scrotum as the parietal layer.[5]
Parietal layer
The parietal layer of tunica vaginalis of testis (lamina parietalis tunicae vaginalis testis)[6] is the portion of the tunica vaginalis that lines the inner surface of the scrotum.[5] It is supported by the internal spermatic fascia.[6]
The cavity of the tunica vaginalis[5] (also: cavum of the tunica vaginalis,[5] or cavum vaginale[citation needed]) is the cavity between the visceral layer and the parietal layer of tunica vaginalis. It is normally occupied by a small amount of clear, lightly coloured fluid.[5]
The volume of the fluid in the cavity may increase abnormally when lymphatic drainage is impeded (due to inflammation, neoplasm, or trauma).[5]
Development
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.[7]
