What is the pathophysiology of pediatric hernias?

Updated: Oct 31, 2018
  • Author: Andre Hebra, MD; Chief Editor: Carmen Cuffari, MD  more...
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The processus vaginalis is an outpouching of peritoneum attached to the testicle that trails behind as it descends retroperitoneally into the scrotum. When obliteration of the processus vaginalis fails to occur, inguinal hernia results. [1] A review of embryonic development of the inguinal region is important to understanding the pathophysiology and surgical management of inguinal hernias.

Although the sex of the embryo is determined at fertilization, the gonads do not begin to differentiate until 7 weeks' gestation. Primordial germ cells migrate along the dorsal mesentery of the gut. They arrive at the primitive gonads early in the fifth week of development and, during the sixth week, invade the genital ridges, which lie on the medial aspect of the mesonephros. The coelomic epithelium proliferates, and the underlying mesenchyme condenses, forming the primitive sex cords.

Under the influence of the Y chromosome, the cords in the male embryo proliferate to form the testes. Near the end of the second month, the testis and mesonephros are attached by the urogenital mesentery to the posterior abdominal wall. As the mesonephros degenerates, only the testis remains suspended. At its caudal end, the attachment is ligamentous and is known as the caudal genital ligament. The gubernaculum, a mesenchymal structure rich in extracellular matrices, also extends from the caudal pole of the testis. This structure attaches in the inguinal region between the differentiating internal and external oblique muscles prior to descent of the testes. As the testes begin to descend at about 28 weeks' gestation, an outgrowth of gubernaculum from the inguinal region grows toward the scrotal area, and as the testis passes through the inguinal canal, this portion of the gubernaculum comes in contact with the scrotal floor.

During this time, the peritoneum of the coelomic cavity is forming an evagination on each side of the midline into the ventral abdominal wall. This evagination, known as the processus vaginalis, follows the path of the gubernaculum testis into the scrotal swellings and forms, along with the muscle and fascia, the inguinal canal. The descent of the testes through the inguinal canal is thought to be regulated by both androgenic hormones produced by the fetal testis and mechanical factors resulting from increased abdominal pressure.

As each testis descends, the layers of the abdominal wall contribute to the layers of the spermatic cord. The internal spermatic fascia is a reflection of the transversalis fascia, the internal oblique muscle helps form the cremaster muscle, and the external spermatic fascia results from the external oblique aponeurosis. In addition, a reflected fold of the processus vaginalis covers each testis and becomes known as the visceral and parietal layers of the tunica vaginalis.

In the female embryo, the ovaries descend into the pelvis but do not leave the abdominal cavity. The upper portion of the gubernaculum becomes the ovarian ligament, and the lower portion becomes the round ligament, which travels through the inguinal ring into the labium majus. If the processus vaginalis remains patent, it extends into the labium majus and is known as the canal of Nuck.

Before birth, the layers of the processus vaginalis normally fuse, closing off the entrance into the inguinal canal from the abdominal cavity. In some individuals, the processus vaginalis remains patent through infancy, into childhood, and possibly even into adulthood. The precise cause of the obliteration of the processus vaginalis is unknown, but some studies indicate that calcitonin gene-related peptide (CGRP), released from the genitofemoral nerve, may have a role in the fusion.

When luminal obliteration fails to occur, a ready-made sac is present where abdominal contents may herniate. Even when the processus vaginalis is patent, the entrance may be adequately covered by the internal oblique and transverse abdominal muscles, preventing escape of abdominal contents for many years. Failure of fusion can result not only in an inguinal hernia, but also in a communicating or noncommunicating hydrocele.

In infants, the most common type of hydrocele is the communicating type. A communicating hydrocele results when the proximal portion of the processus vaginalis remains patent, allowing fluid from the abdominal cavity to freely enter the scrotal sac. When closure is present proximally but fluid remains trapped within the tunica distally, a noncommunicating hydrocele results.

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