113 Hernias

Hernias—defined as a protrusion of a structure or part of a structure through tissues normally containing it—are encountered frequently in pediatric clinical practice. In children, external hernias represent the vast majority and are typically in, but not limited to, the inguinal and umbilical regions. Umbilical hernias are very common, most notably in premature infants, infants of African and African American descent, and infants with certain diseases or genetic syndromes. It is estimated that inguinal hernias occur in roughly 1% to 5% of all children, with an increased incidence in specific populations such as those with a family history of inguinal hernia and premature infants, who can have an incidence near 30% in those with birth weights less than 1000 g. Inguinal hernias can cause significant morbidity because of incarceration and strangulation, making it essential that general practitioners and subspecialists alike understand how to approach the condition and recognize when emergent therapy is required.

Congenital diaphragmatic hernia (CDH) and hiatal hernia are the two most common internal hernia types among children. CDH is a neonatal surgical emergency that presents with a scaphoid abdomen, cyanosis, and respiratory distress within minutes of birth as a result of the herniation of abdominal contents into the thoracic cavity (Figure 113-1 see Chapter 102). Hiatal hernias, in which intraabdominal portions of the esophagus, the stomach, or both pass into the thorax, are less common in children than adults but remain an important consideration in certain clinical circumstances. Other internal hernias, including paraduodenal and mesenteric hernias, occur within the abdominal cavity. These are largely the result of congenital abnormalities and in rare circumstances become clinically relevant in childhood.

Figure 113-1 Congenital diaphragmatic hernia.

Etiology and Pathogenesis

External Hernias

Inguinal Hernia

Indirect inguinal hernias are congenital in origin, arising from incomplete embryogenesis. In boys, the testes are initially in a retroperitoneal position. A portion of peritoneum called the processus vaginalis attaches to the testes and precedes the testicular descent through the internal inguinal ring into the scrotal sac. The testes are located at the internal inguinal ring by 28 weeks of gestation and reach their final destination by 36 weeks with the left side completing its descent slightly earlier than the right. The processus vaginalis creates a patent conduit between the abdomen and the scrotum via the inguinal canal and typically obliterates between 36 and 40 weeks of gestation or in the postnatal period. If the processus vaginalis remains patent, abdominal contents may escape through the internal inguinal ring into the inguinal canal and the scrotum (Figure 113-2).

Figure 113-2 Indirect inguinal hernia.

In girls, the ovaries also start in a retroperitoneal position; however, their descent is modified, and they do not leave the abdominal cavity. The processus vaginalis extends through the inguinal canal with the round ligament to the labia majoris and usually obliterates between 32 and 36 weeks of gestation. This embryologic difference is likely why indirect inguinal hernias occur six times more commonly in boys than girls.

Patients with cryptorchidism (failure of one or both testicles to descend into the scrotum), urogenital malformations, and increased intraabdominal pressure are at increased risk for developing indirect inguinal hernias. Direct inguinal hernias are rare in children, entering the inguinal canal through a defect in the posterior wall of the canal medial to the inferior epigastric vessels. Femoral hernias, also rare in children, penetrate an acquired muscular defect in the abdominal wall posterior to the inguinal ligament. Patients with connective tissue disorders and those who have had previous surgery to correct an inguinal hernia have greater risk for femoral or direct inguinal hernias.

Umbilical Hernia

All newborns have a natural defect at the umbilicus, allowing the cord with the umbilical vessels to pass through. In most infants, the umbilical ring closes spontaneously. In some, an anatomic defect persists, increasing the likelihood of herniation. The umbilical vein obliterates and becomes the ligamentum teres, which usually attaches to the umbilical ring inferiorly. A superior attachment may occur, leaving an area of potential weakness. The umbilical ring is also supported by the transversalis fascia and peritoneum. A natural thickening of the transversalis fascia occurs at the umbilicus, which may fail to cover the entire ring, leaving an area of relative weakness. The closure of the ring is most likely multifactorial as suggested by significant racial differences in incidence of hernia and increased frequency in children with Beckwith-Wiedemann syndrome; Hurler’s syndrome; trisomies 13, 18, and 21; and congenital hypothyroidism.

Abdominal Wall Hernias

Epigastric hernias occur above the umbilicus through a defect in the linea alba and most commonly contain preperitoneal fat. Such a defect develops when there is failure of complete approximation of the midline during the final stages of abdominal wall formation. Incisional hernias, resulting from incomplete healing of a surgical incision, can occur anywhere on the abdomen. Any process that increases intraabdominal pressure, obesity, and postoperative wound infections are major risk factors for incisional hernias. Spigelian hernias, reported rarely in children, occur in an area of natural weakness at the lateral edge of the rectus abdominus muscle and below the arcuate line where only transversalis fascia lies posterior to the rectus abdominus (Figure 113-3).

Figure 113-3 Abdominal wall hernias.

Internal Hernias

Hiatal Hernia

The intraabdominal esophagus and the stomach are secured in place by numerous fascial and ligamentous elements. At its entry into the abdomen, the esophagus is supported by fibroelastic tissue called the phrenoesophageal membrane. This membrane, as well as many other supporting structures, can be structurally deficient at birth or gradually weaken with time and stress, causing laxity of the support and widening of the muscular hiatus. During inspiration, the transdiaphragmatic pressure differential causes the esophagus and stomach to be pulled upward. Depending on the areas of weakness, the gastroesophageal junction may slide into the posterior mediastinum or a portion of the stomach may pass through the hiatus alongside the esophagus with the lower esophageal sphincter maintained in its correct anatomic position (Figure 113-4).

Figure 113-4 Hiatal hernias.

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