Omphalocele and gastroschisis are the 2 most common congenital abdominal wall defects. They are distinct genetic and clinical entities. With omphalocele, there is failure of the midgut to return to the intraembryonic coelomic cavity. The affected infant has herniation of abdominal viscera into the base of the umbilical cord. The herniated organs are contained within a sac consisting of parietal peritoneum and amnion. A small omphalocele may contain only intestine, whereas a larger defect sometimes includes herniation of the liver. With gastroschisis, there is herniation of abdominal contents through a defect in the abdominal wall located to the right of an intact umbilical cord. There is no enveloping sac with gastroschisis, and the herniated intestine moves freely in amniotic fluid.¹

Omphalocele occurs in 1 to 2 per 10,000 livebirths. Chromosomal anomalies are present in 30% to 40% of these children, including 45XO (Turner syndrome), triploidy, and trisomies 13, 18, and 21. Associated structural anomalies are present in 50% to 70% of infants with omphalocele, such as congenital heart disease (30% to 40%), genitourinary anomalies (40%), diaphragmatic hernia, musculoskeletal anomalies (20%), and otopalatodigital syndrome. Omphalocele is a component of pentalogy of Cantrell, which includes diaphragmatic hernia, malformation of the inferior aspect of the sternum, pericardial defects, and cardiac defects, in addition to omphalocele. Omphalocele can also occur in infants with Beckwith–Wiedemann syndrome, and is a component of the omphalocele–exstrophy–imperforate anus syndrome (OEIS complex: omphalocele, exstrophy of the cloaca, imperforate anus, and spinal anomalies). Posterior meningocele occasionally occurs in these children. Garonchi-Baruch syndrome includes omphalocele, heart anomalies, diaphragmatic hernia, liver cyst, and radial ray defects. PAGOD syndrome refers to pulmonary anomalies, agonadism, omphalocele, diaphragmatic defects, and dextrocardia.^2–5

During normal embryonic development of the midgut, there is rapid elongation of the gut and its mesentery. During this phase of rapid growth, there is insufficient volume within the abdominal cavity for the bowel, and loops of intestine extend into the extraembryonic coelom of the umbilical cord. This physiologic umbilical herniation occurs during the 6th week of development, and the intestines normally return to the abdominal cavity during the 10th week. Complete reduction of this physiological midgut hernia should occur by 12 weeks gestation. Omphalocele may be due to simple failure of this physiological midgut hernia reduction. Failure of midline fusion of the embryonic lateral mesodermal folds may also be involved in the pathogenesis. Ectopia cordis occurs with developmental failure of the cephalic fold in addition to deficiency of the lateral folds. Failure of development of the caudal fold results in cloacal exstrophy.⁶

Prenatal sonography demonstrates an omphalocele as a midline ventral mass that contains herniated viscera. There is a surrounding membrane. The umbilical cord inserts into the sac. One or more umbilical cord cysts are sometimes present. Fetal ascites is common. Careful examination for other structural anomalies is mandatory. If there are no other structural abnormalities and amniocentesis demonstrates a normal fetal karyotype, there is a favorable prognosis. Followup sonography occasionally documents spontaneous resolution of a small fetal omphalocele (i.e., transient omphalocele).

Radiography of the newborn with omphalocele shows a midline anterior extraabdominal mass that contains bowel (Figure 39-1). Herniation of a portion of the liver is common. Infants with a large omphalocele often have a small thoracic cavity and pulmonary hypoplasia. Potential radiographic findings of anomalies that can occur in association with omphalocele include cleft sternum, ectopia cordis, lumbar spine anomalies, and an absent radial ray. Children with repaired omphalocele have manifestations of intestinal malrotation on contrast studies. Gastroesophageal reflux is common.⁷

Gastroschisis is a congenital right paraumbilical abdominal wall defect. There is herniation of the fetal midgut through the defect. The herniated bowel floats freely in the amniotic fluid. Gastroschisis occurs in approximately 2 per 10,000 livebirths. Associated anomalies occur in 5% to 10% of infants with gastroschisis. Chromosomal anomalies are uncommon. There is an association with intestinal hypoperistalsis and intestinal atresias, due to exposure of the bowel to amniotic fluid or mechanical compression of the exposed bowel. Potential complications in the infant with repaired gastroschisis include necrotizing enterocolitis and obstructive adhesions.

The imaging hallmark of gastroschisis is herniation of intestine through an anterior abdominal wall defect without a surrounding membrane (Figure 39-2). Typically, there is herniation of small intestine, large intestine, and stomach. Occasionally, the bladder herniates. Unlike omphalocele, herniation of the liver does not occur. In those newborns with associated atresia, imaging studies show bowel dilation proximally. Most atresias in gastroschisis patients are in the jejunum or ileum. Prenatal sonography of gastroschisis often shows dilation and thickening of the herniated intestine. The umbilical cord is to the left of the defect. Fetal ascites is lacking.

Children with a history of repaired gastroschisis invariably have intestinal malrotation. Abdominal radiographs and contrast studies may demonstrate intestinal dilation due to hypoperistalsis. Other potential findings include cryptorchidism, gallbladder hypoplasia, and hiatal hernia.

The umbilical region includes the umbilicus itself, the umbilical ring, and the adjacent tissues of the anterior abdominal wall. Embryonic structures of the umbilicus that can be involved in developmental lesions include the omphalomesenteric duct, the urachus, and the umbilical vessels. Meckel diverticulum is the most common anomaly of the omphalomesenteric duct. Fistulas, cysts, and sinus tracts involving the umbilicus are additional potential anomalies related to the omphalomesenteric duct. Urachal connections can also lead to cysts, fistulae, and sinus tracts. With an omphalomesenteric duct fistula, the connection is with the intestine (nearly always the distal ileum), whereas a urachal fistula connects to the bladder. Abnormal development of the umbilical ring and umbilicus is an important component of omphalocele, gastroschisis, and umbilical hernia.⁸

The umbilicus is clinically normal in most patients with Meckel diverticulum. There is discussion of the clinical and radiographic features of Meckel diverticulum and other omphalomesenteric duct anomalies in Chapter 36. The clinical feature that suggests the presence of an omphalomesenteric fistula is umbilical leakage of fluid that has characteristics of small intestine contents. An omphalomesenteric sinus drains small amounts of mucus (secreted by the small intestine mucosa that lines the tract). The drainage that occurs with a patent urachus represents urine. A urachal sinus typically drains small amounts of clear or serous fluid.