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.

Other Internal Hernias

Paraduodenal hernias occur when small bowel protrudes through a fossa created by abnormal mesenteric attachments to the ascending or descending colon. A congenital or acquired defect in the mesentery itself may accept a loop of bowel anywhere along its tract known as a mesenteric hernia.

Clinical Presentation

External hernias classically present with the history of an intermittent or persistent swelling without associated pain, which may disappear spontaneously and are most noticeable with crying or straining.

Inguinal hernias can present at birth or any time during childhood. The history may include a description of the bulge extending to the scrotum or labia majora. The differential diagnosis of an inguinal-scrotal or labial swelling also includes incarcerated inguinal hernia, hydrocele, torsion of an undescended testis, and inguinal lymphadenitis. History and a detailed gastrointestinal (GI) and genitourinary examination should differentiate between these entities (Table 113-1). Observing the mass increasing in size during a period of increased intraabdominal pressure and decreasing in size during relaxation or gentle taxis strongly suggests the diagnosis of inguinal hernia. A firm, smooth mass is often palpable at the external inguinal ring. The smooth sensation of the herniated sac rolling over itself when palpated at the pubic tubercle is known as the “silk glove sign” and supports the diagnosis of hernia. Transillumination is not specific for hydroceles and should be used with caution as a tool to differentiate from hernias. Hernias may transilluminate as well, especially in the incarcerated state with excess bowel wall edema. Close inspection of the contralateral inguinal region is important because 10% of patients have bilateral inguinal hernias. Determining if the hernia is indirect or direct is frequently difficult on examination and is often not confirmed until surgery. A femoral hernia is clinically seen as a swelling in the femoral canal inferior to the inguinal ligament but may also be confused for an inguinal hernia.

Table 113-1 Differential Diagnosis of Inguinal-Scrotal or Labial Swelling

Umbilical hernias typically present with the history of an external hernia described above. The physical examination reveals a soft mass covered by skin protruding from the umbilicus, increasing in size with increased intraabdominal pressure, and reducing easily and completely in all but the rarest of circumstances. The differential diagnosis for an umbilical mass in a young child also includes umbilical pyogenic granuloma, umbilical polyp, omphalocele, and an omphalomesenteric duct remnant. The umbilical granuloma and polyp are readily differentiated from hernia by the lack of skin covering the mass, reddish color, and serous drainage that may be present. Omphalocele should be detected at birth, if not earlier, with intestine protruding from the umbilicus covered only by a membranous sac. Exceedingly rare umbilical tumors, such as teratomas and sarcomas, have been reported; these are not soft or reducible on examination.

Internal hernias are frequently asymptomatic and may come to the clinician’s attention during an unrelated investigation. When symptomatic, the presentation is variable and depends on the site of herniation.

The cardinal symptoms of a sliding hiatal hernia are regurgitation and heartburn, which are manifestations of gastroesophageal reflux (GER; see Chapter 107). When a hiatal hernia is the underlying cause, GER may be associated with complications such as pulmonary infections secondary to aspiration, vomiting, and failure to thrive. Dysphagia may also be described but tends to be a later finding. Paraesophageal hiatal hernias can present in similar fashion to a sliding hernia; however, dysphagia, early satiety, and chest pain tend to be more prominent with paraesophageal hernias. Sliding and paraesophageal hiatal hernias should be considered as part of the differential diagnosis for any of these presenting symptoms. The physical examination may provide insight to the presence of GER but is not helpful in making the diagnosis of either type of hiatal hernia.

Paraduodenal, mesenteric and other types of internal hernias contained within the abdominal cavity rarely cause symptoms during childhood. When problematic, these hernias usually present with a constellation of symptoms, including abdominal pain, vomiting, decreased stooling, and irritability as manifestations of acute or recurrent intestinal obstruction.

Evaluation and Management