Definitions and Epidemiology
Abdominal wall defects in children present as a range of anomalies, from minor hernias of the umbilical or inguinal region to major protrusions of the abdominal wall, such as omphaloceles and gastroschisis. The range of care for these defects spans elective outpatient surgery to emergent care with extended stays in the neonatal intensive care unit. Advances in medical care have greatly improved the survival of infants born with congenital abdominal wall defects such as gastroschisis and omphalocele. Advances include parenteral nutrition, perinatal care, and surgical techniques when primary closure is not possible. However, after the perinatal period challenges for these children with abdominal wall defects may continue for some time.
Abdominal wall hernias are very common in the pediatric population, and the surgical treatments are among the most common procedures performed by pediatric surgeons. Hernias are defined by location as well as reducibility. Reducibility will dictate treatment management of a hernia. A reducible hernia allows the patient or examiner to place the abdominal contents back into the abdominal cavity with palpation. An incarcerated hernia is one in which reduction of the abdominal contents is not possible. A strangulated hernia is an incarcerated hernia that is being rendered ischemic by loss of blood supply, a true surgical emergency.
Epigastric hernias are small midline protrusions located between the umbilicus and the xiphoid process. These hernias have no sac and consist of preperitoneal fat protruding through a small fascial defect. Although small, epigastric defects do not close spontaneously and operative closure is recommended to avoid symptomatic fat entrapment. Umbilical hernias develop when the umbilical ring is unsupported, and the rectus muscles fail to approximate in the midline and close the fascial ring through which the umbilical cord protrudes.1
The most common hernia treated by pediatric surgeons is an inguinal hernia. Inguinal hernias are formed by failure of the processus vaginalis to completely close, leaving a potential peritoneal diverticulum into which abdominal viscera may herniate or into which fluid can accumulate and form a cystic fluid-filled cavity (hydrocele). In males, persistent patency of all or part of the processus vaginalis may result in various anomalies, including an inguinal hernia (Figure 14–1), a scrotal hernia (Figure 14–2), a communicating hydrocele, a hydrocele of the spermatic cord (Figure 14–3), and a scrotal hydrocele. In females, inguinal hernias and hydroceles can present as a protrusion or mass in the labia majora but arise far less commonly due to the absence of gonadal descent (Figure 14–4).
Urachal remnants involve the embryologic urachus, a cord-like structure that extends from the dome of the bladder to the inferior border of the umbilical ring, which has failed to obliterate. An embryologic remnant, the omphalomesenteric duct is a normal developmental structure that connects the fetal gut with the yolk sac and subsequently obliterates. Failure of obliteration may result in the formation of a polyp, fistula, cyst, fibrous band, sinus, or Meckel’s diverticulum.
Gastroschisis is a defect of the anterior abdominal wall in which the viscera extrude and are not covered by amnion or a peritoneal membrane. This defect almost always occurs to the right of the umbilical cord (Figure 14–5). Gastroschisis is not usually associated with other anomalies and chromosomal syndromes as is the case in omphalocele; however, intestinal atresia may be present in 10% of patients with gastroschisis.2
Omphalocele is a herniation of abdominal contents through the umbilical ring (Figure 14–6). The herniation (also known as exomphalos) is covered by a sac composed of an outer layer of amnion and an inner layer of peritoneum. Approximately 50% of patients with omphalocele will have anomalies of the cardiovascular, alimentary, genitourinary, musculoskeletal, and/or CNS. Various defined syndromes and trisomies are associated with omphaloceles.2–4
Abdominal wall defects can be associated with other organ system anomalies beyond the GI tract, including pentalogy of Cantrell (ectopia cordis, pericardial and diaphragmatic defects, cardiac defects, cleft sternum, and omphalocele) (Figure 14–7) and cloacal exstrophy (imperforate anus, omphalocele, exstrophy of the bladder, and lower neural tube defects) (Figure 14–8). A less dramatic abdominal wall defect is an umbilical cord hernia. This is a small (<4 cm) anomaly with a thin membrane and usually only contains the midgut. This occurs because the midgut fails to completely return to the abdominal cavity at 10–12 weeks gestation. This defect can almost always be closed primarily, via a simple closure following reduction of the prolapsed bowel. Unlike simple umbilical hernias, these do not usually close spontaneously.
The overall prevalence of abdominal wall defects is 4–5 per 10,000 live births; with the increased use of prenatal ultrasound this has been reported to be as high as 1 in 2500 fetuses. The incidence of omphalocele is historically reported as 1 in 4000 births and gastroschisis as 1 in 6000–10,000 births. The incidence of gastroschisis is increasing in reports from both the United Kingdom and the United States and gastroschisis is becoming more frequently encountered than omphalocele in clinical practice. Male and female infants are equally affected.2,3,6
A basic understanding of the embryology of the anterior abdominal wall is necessary to understand the pathogenesis of abdominal wall defects. During the first 3 weeks of gestation, the body is a disc-like structure between the chorion and the amnion. Around the fourth week of gestation, the formation of a body cavity begins with the inversion of the lateral edges of the body disk. The division of thoracic and abdominal cavities is performed by the descent of the cephalic fold, which brings the embryologic heart downward, as the septum transversum. The cephalic fold components will contribute to the thoracic and epigastric walls. Failure of these mesodermal myotomes in the upper midline to fuse leads to the defect known as pentalogy of Cantrell. The caudad fold moves upward to form the infraumbilical abdominal wall and bringing the bladder (allantois) upward, additionally contributing to the hindgut and hypogastric wall. Failure of the urorectal septum to rise and separate will result in cloacal exstrophy. The lateral folds will develop into the midgut and lateral abdominal wall.2–6
At this point, the primitive gut is a straight tube in continuity with the yolk sac, which will diminish, leaving a solid umbilical stalk. The fifth to sixth weeks of gestation marks the rapid growth of the midgut (a.k.a. primary intestinal loop) and a physiologic herniation occurs through the umbilical ring into the umbilical coelom. The formation of the umbilical/extraembryonic coelom is formed (5–6 weeks gestation) by coalescence of vacuoles of Wharton’s jelly within the umbilical stalk. At the 10–12th weeks of gestation, the embryonic gut returns to the abdominal cavity and undergoes a 270˚ (counter-clockwise) rotation around the superior mesenteric artery.2,6
During the development of the anterior abdominal wall, the anatomic structures of the umbilical ring include: the allantois, four umbilical vessels (two arteries and two veins), the vitelline duct, vitelline vessels, and the umbilical/extraembryonic coelom. At the fifth week of gestation the right umbilical vein resorbs, leaving the left umbilical vein to return placental blood to the heart. This involution may create a weakness on the right side of the umbilical cord. When the midgut returns to the abdominal wall, the allantois, vitelline duct, and vitelline vessels are obliterated. This process leaves the paired umbilical arteries and left umbilical vein remaining in the umbilical ring.
The development of a patent processus vaginalis and subsequent inguinal hernia is based on descent of the testis. Under typical conditions, the internal inguinal ring closes and the lumen of the processus vaginalis, an outpouching of the peritoneal cavity, obliterates above the testis (Figure 14–9).
Urachal remnants are formed if the mucosa-lined urachus does not obliterate. One of the following five uncommon anomalies can occur: (1) congenital persistence of a patent urachus, causing a fistulous tract joining the bladder lumen and the umbilicus. Surgical repair consists of urachal tract excision and ligation at the bladder junction. (2) A remnant urachal sinus opens to the umbilicus, while a (3) urachal diverticulum opens to the bladder. (4) A urachal cyst forms anywhere along the urachal tract but does not communicate with either the umbilicus or the bladder. (5) An alternating sinus is a cyst-like structure that can drain into either the bladder or the umbilicus. Diagnosis and differentiation of these anomalies is aided by fistulography, ultrasound, and/or CT scan.7
The earlier the embryologic abnormality manifests, the more complex and usually devastating the anomaly (Table 14–1). Abdominal wall defects can occur because of: (1) failed mesoderm migration and decreased apoptosis, (2) failure of the yolk sac and body stalk to approximate with the amnion, (3) lack of the umbilical ring development, and (4) abnormal neuronal differentiation.
|Development of four folds to form body cavities
|Anterior abdominal wall development, development of umbilical coelom
|Failure of folds to develop
|Body stalk defect
|Umbilical coelom develops, atrophy of right umbilical vein
|Failure of coelom development or vascular accident
|Myotome fusions in midline
|Defective fusion of midline cranial fold
|Pentalogy of Cantrell
|Defective fusion of midline caudal fold
|Bladder or cloacal exstrophy
|Development of cloacal membrane and urorectal septum
|Abnormal development of urorectal septum
|Herniation of bowel and return to abdominal cavity
|Failure of lateral folds to fuse
|Bowel undergoes rotation and fixation
|Failure of appropriate rotation and fixation
Gastroschisis develops between the sixth and seventh weeks of gestation, believed to be caused by vascular compromise to the right-sided abdominal wall. The gestational timing of gastroschisis coincides with the obliteration of the right umbilical vein. Early obliteration of the right umbilical vein or persistence of the vessel, interfering with the development of collateral circulation, has been used to explain this ischemic event. Another unproven, but possible, explanation is that simple separation of the cord occurs from the umbilical ring on the right side of its attachment. Indirect evidence of this may be encountered from the clinical observation of spontaneous closure of the umbilical port with simple reduction of the bowel without fascial repair. Normal abdominal wall development is present. A rare occurrence is prenatal rupture of an omphalocele. The infant presents with an abdominal wall defect with the appearance of gastroschisis, but with abnormal abdominal wall development.
Omphalocele is believed to develop from failure of the lateral folds to migrate and fuse appropriately at the umbilical ring, resulting in continued herniation of the midgut. The fascial defect can vary widely from small (i.e., congenital hernia of the umbilical cord) to large (>12 cm). Giant omphaloceles can present with the entire gastrointestinal system, liver, spleen, bladder, and gonads outside of the abdominal cavity. These cases are extremely difficult to treat because without intra-abdominal organs the abdominal cavity loses domain and fails to grow.
Multiple studies have been performed to address possible maternal and environmental factors that may attribute to the development of abdominal wall defects. Epidemiologic and animal models suggest possible causal factors, including use of cyclooxygenase inhibitors (ibuprofin and aspirin) during gestation, and recreational and illicit drugs (nicotine and cocaine), and are also associated in children of women with multiple children who have different fathers.8–11 Maternal obesity has been shown to increase the risk of omphalocele; however, a recent meta-analysis suggests that obesity reduces the risk of gastroschisis.12,13 Gastroschisis is associated with young maternal age.14 Additional medications producing vasoconstriction early in pregnancy increase the risk of gastroschisis; this includes common medications for colds, cough, and pain.15 Omphalocele can present either independently or with other associated anomalies. There are no environmental factors or teratogens identified that are associated with isolated omphalocele. In a single study, preconceptional multivitamin use was associated with a 60% reduction in the risk for non-syndromic omphalocele.16
Umbilical hernias most commonly present during the early months of infancy and occur more frequently in Black, low-birth-weight, and premature infants. Most umbilical hernias are isolated findings, but some are associated with other disorders including Beckwith–Wiedemann syndrome (omphalocele–macroglossia–gigantism), hypothyroidism, mucopolysaccharidosis, and Down’s syndrome (trisomy 21).17 Concomitant inguinal hernias are noted in about 15% of children with umbilical hernias.18 Umbilical hernias are rarely symptomatic and infants are commonly brought for medical evaluation because of family concern. Palpation of the umbilicus reveals a well-defined rim that surrounds the umbilical defect.
The clinical presentation of inguinal hernias can vary between premature infants and children. Inguinal hernias arise in about 10% of preterm infants. Bilateral inguinal hernias also occur more commonly in preterm infants.19 The risk of incarceration of a hernia in a preterm infant is two to five times greater than the risk in older children (30% versus 6–15%).20 Repair of incarcerated hernias and large hernias in preterm infants can be very difficult due to the inflammatory changes and tissue-paper consistency of structures in the inguinal region.
Approximately 4% of term infants are born with a congenital indirect inguinal hernia. Inguinal hernias occur on the right in 60%, on the left in 30%, and bilaterally in 10% of cases. The increased incidence of right-sided hernias may be related to later descent of the right testis and delayed obliteration of the processus vaginalis.21 Inguinal hernias in boys usually present as a bulge in the groin that is more apparent with crying or straining and may extend into the hemiscrotum. Inguinal hernias may reduce spontaneously when the child relaxes, or be reduced manually with gentle pressure. Once the hernia is reduced, digital pressure on the external ring will prevent re-herniation of the viscus. Inguinal hernias in females present as a bulge in the superior aspect of the labia majora. A palpable mass may represent a herniated ovary. If gonads are palpable bilaterally in female patients, one should suspect androgen insensitivity syndrome (formerly known as testicular feminization syndrome).
Incarceration is the most common complication of inguinal hernias and occurs in up to 10% of children overall. In the first year of life, the incidence is higher and incarceration is reported to occur in as many as 31% of children with hernias.22 Presenting symptoms of an incarcerated inguinal hernia include irritability, pain, abdominal distension, and vomiting. Small bowel obstruction may occur if the entrapped mass becomes edematous. Examination of an incarcerated hernia usually reveals a tender, firm, erythematous mass in the inguinal region (Figure 14–10). Edema of the groin and scrotal skin may also be present. In girls, a palpable, irreducible ovary occurs in 15% of inguinal hernias and despite possible incarceration and strangulation of the ovary, intestinal symptoms will be absent in these children. A bimanual technique should be used when attempting reduction. Digital manipulation with one hand compresses the hernia, while the other hand, placed over the external ring, guides the hernia through it.
Abdominal wall defects can present either at birth or with prenatal diagnosis from a maternal screening ultrasound. Pregnant women may present with an elevated alpha-fetoprotein (maternal serum alpha-fetoprotein (msAFP)) on a maternal triple-screen evaluation. The sensitivity of msAFP for gastroschisis is higher than for omphalocele, but a majority of omphaloceles do have an elevated msAFP.23 Additionally, elevated msAFP is an indication to proceed with a fetal ultrasound. A maternal ultrasound after 12 weeks gestation can identify abdominal wall defects because, at this point in gestation, the midgut has usually returned to the abdominal cavity.24 Detailed description of ultrasound and triple screen will be addressed in the section “Diagnostic Tests.”
Infants who are diagnosed at delivery with an abdominal wall defect must be assessed for the type of defect by working through the differential diagnosis (discussed in the following section). Infants diagnosed with an omphalocele require ultrasound examination to identify other congenital abnormalities prior to proceeding with definitive repair, as these abnormalities may affect anesthesia. The clinical presentations of other abdominal wall defects such as pentology of Cantrell and cloacal exstrophy are similar to omphalocele and gastroschisis but require a multidisciplinary approach with cardiothoracic surgery for pentology of Cantrell and urology and orthopedic surgery for cloacal exstrophy.
The differential diagnosis is listed in Table 14–2. Umbilical hernias are usually quite straightforward to diagnose on exam; however, masses and discharges from the umbilicus may be incorrectly referred as an umbilical hernia.
|Umbilical pyogenic granuloma
|Omphalomesenteric duct remnant