The secondary external inguinal ring and associated fascial planes: surgical anatomy, embryology, applications

Classically, two inguinal rings are defined: internal and external. We previously introduced a third one, the secondary internal inguinal ring, deep to the classic internal. Here, we present a fourth ring, the secondary external inguinal ring, initially described by McGregor (Surg Gynecol Obstet 49:273-307, 1929), but now forgotten. Embryologically, this ring may be formed by evagination of Scarpa's fascia during testicular descent. Anatomically, it is located 2 cm below the pubic tubercle. It is formed by Scarpa's fascia that covers the spermatic cord anteriorly; medial and lateral fascial reflections delineate the ring and form the spermatic cord canal. The cord is attached to the posterior wall of the canal. The canal ends at the entrance of the scrotum, where Colles' fascia fuses with coverings of the cord. Adjoining the secondary external ring, at the same surgical layer and communicating with the subcutaneous abdominal space, are four subcutaneous pouches: laterally, the superficial inguinal pouch; medially, the perineal, femoral, and pubic pouches. Surgically, an inguinoscrotal hernia passes though the secondary external ring and obtains an extra outer layer by entering the spermatic cord canal. Underdevelopment of the ring leads to incomplete testicular descent or ectopic testis. We recommend reconstruction of Scarpa's ring after orcheopexies and herniotomies in children. After urethral rupture distal to the urogenital diaphragm, urine may fill the subcutaneous abdominal space, pouches, and scrotum, due to their communication around the secondary external ring. In females, this ring was not found, possibly because of the non-descent of the ovaries through (and beyond) the inguinal canal.