Chapter 103. Inguinal Canal Development and Testicular Migration - Review of Medical Embryology Book

Inguinal canal development: the canals form the pathways for the testes to descend through the abdominal wall into the scrotum. They develop in the female embryo as well as in the male, even though the ovaries (except in rare cases) do not enter the canals

AS THE MESONEPHROS degenerates, the gubernaculum (a ligament) descends on each side from the lower poles of the gonads, passes obliquely through developing abdominal wall, and attaches to the labioscrotal swellings (future scrotum or labia majora)
THE PROCESSUS VAGINALIS (peritoneal sac) develops later, on each side, ventral to the gubernaculum, and herniates through the lower abdominal wall along the pouch formed by the gubernaculum

Each processus carries extensions of layers of the abdominal wall before it, and together they form the walls of the inguinal canal. In the male, they also form the coverings for the testes and the spermatic cord
The opening produced in the transversalis fascia by the processus is the deep inguinal ring and that in the external oblique aponeurosis becomes the external or superficial inguinal ring. Between the rings is the inguinal canal.

Testicular migration: the testes migrate from their early developing lumbar position, in the dorsal abdominal wall, to the deep inguinal rings above the scrotum between month 3 and term. Migration takes place as the pelvis enlarges and the embryonic trunk enlarges and, because the gubernaculum does not grow as fast as the body wall, the testes descend. Their descent through the inguinal canals into the scrotum is probably due to hormones (androgens and gonadotropins)

THE VAGINAL PROCESS, a bilateral prolongation of the coelomic cavity peritoneum, is protruded into the scrotum

The vaginal process at first is mostly open, but progressively narrows, and finally its proximal portion is entirely obliterate The remainder of the process, in the scrotum, then exists as a double serous envelope around the testes, called the tunica vaginalis
The vaginal process (processus vaginalis) is parallel with the inferior ligament of the testis, which becomes the gubernaculum testis. The migration of the testes follows the line of the gubernaculum, although the role of the gubernaculum is uncertain
Descent through the inguinal canal begins during week 28 and takes 2 to 3 days. The testes move beneath the peritoneum (retroperitoneal) and behind the processus vaginalis

The testes reach the orifice of the inguinal canal around month 6, cross the canal during month 7, and arrive at their definitive intrascrotal position near the end of month 8
After the testes pass into the scrotum, the inguinal canal contracts around the spermatic cor In full-term newborn boys, over 97% have bilateral descended testes. Some, however, may descend during the first 3 months after birth

ANOMALIES OF TESTICULAR MIGRATION are many and are not necessarily related to a hormonal deficit since they are often unilateral. They range from simple ectopy, where the testis may be inguinoscrotal or inguinal, to cryptorchism, where the testis is pelvic, iliac, or even lumbar

The gland also may be in an aberrant location such as crural or perineal
Cryptorchism usually results in an alteration in spermatogenesis or, if bilateral, even sterility

ANOMALIES OF VAGINAL PROCESS CLOSURE are also frequent. They may be (not always) associated with problems of testicular migration

Cysts of the spermatic cord are signs of incomplete closure
A complete failure of closure may result in congenital oblique external hernia or the so-called communicating hydrocele