133: Surgical Diseases of the Newborn: Abdominal Wall Defects

A gastroschisis is a centrally located, full-thickness abdominal wall defect with 2 distinct anatomic features.

1. The extruded intestine is never covered by a protective sac.

2. The umbilical cord is an intact structure at the level of the abdominal skin, just to the left of the defect. Typically, the abdominal wall opening is 2–4 cm in diameter, and the solid organs (liver and spleen) reside in the peritoneal cavity.

Exposure to irritating amniotic fluid renders the intestines edematous, indurated, and foreshortened. Appropriate peristalsis and effective intestinal absorption are significantly delayed, usually by several weeks. Associated congenital anomalies are rare.

The infant is born with varying amounts of intestine extruding through the defect. An inflammatory peel is often found on the intestines. Up to 10% of neonates with gastroschisis will have an associated intestinal atresia.

Although readily apparent in most cases, gastroschisis must be differentiated from ruptured omphalocele. Increasingly, prenatal ultrasonography identifies gastroschisis

1. General considerations. Infants with gastroschisis should be delivered at a neonatal center capable of providing definitive care. Both vaginal and cesarean deliveries have been shown to be safe and should be left to the obstetrician's discretion.

2. Specific measures

   1. Fluid resuscitation. Venous access should be obtained promptly and aggressive fluid resuscitation should be initiated to combat the large evaporative fluid losses from the exposed bowel.

   2. Temperature regulation. Immediate attention should be directed toward maintenance of normal body temperature. The tremendous intestinal surface area exposed to the environment puts these infants at great risk for hypothermia.

   3. Protective covering/position. To prevent evaporative heat loss, the bowel should be covered with a moist, clean dressing. The abdomen should be wrapped in layers of cellophane, or the baby's abdomen, bowel, and legs should be placed in a plastic bag. The newborn should be laid on its side to prevent “kinking” the intestine's vascular pedicle while awaiting surgical intervention.

   4. Nasogastric/orogastric decompression. This is helpful.

   5. Broad-spectrum antibiotic coverage. Appropriate given the unavoidable contamination.

   6. Total parenteral nutrition. Delayed bowel function should be expected, and appropriate intravenous nutritional support must be provided.

   7. Surgical correction. As soon as the infant's condition permits, operative correction should be undertaken. In some babies, reduction of the herniated intestine and primary closure of the abdominal wall can be performed. Others require placing the intestines in a protective silo with subsequent staged reduction. Central venous access is usually part of the surgical intervention.

An omphalocele is a herniation of abdominal contents into the base of the umbilical cord. The gross appearance of omphalocele differs from that of gastroschisis in 2 important respects:

1. The malpositioned abdominal contents are covered by a protective membrane (unless antenatal rupture has occurred).

2. Elements of the umbilical stalk course individually over the sac and come together to form a normal-appearing umbilical cord.

Significant congenital anomalies occur in 50% of infants with omphalocele. Chromosomal abnormalities, cardiac defects, and congenital diaphragmatic hernia are common.

The size of the omphalocele varies. Typically, smaller defects contain intestine only. Large or giant omphaloceles (<5 cm) may also contain liver and spleen. The peritoneal cavity may be small because growth has proceeded without the solid organs in proper position.

The anomaly is usually apparent. A ruptured omphalocele may be confused with a gastroschisis, but infants with omphalocele do not possess an intact umbilical cord at the level of the abdominal wall. Careful studies to identify associated congenital anomalies should be performed.

Reduction, even when staged over a lengthy period, may be difficult to achieve. Infants fall into 2 treatment groups:

1. Ruptured sac. A ruptured omphalocele resembles a gastroschisis. Care of the unprotected intestines is as described for gastroschisis (see previous text). Emergent surgical intervention is necessary.

2. Intact sac. An intact omphalocele is a less urgent surgical problem. The omphalocele sac conserves heat, prevents evaporative loss, allows effective peristalsis, and must be protected. Timing of surgery is determined by the size of the defect, gestational age, and presence of other congenital anomalies. Primary closure can be attempted in neonates with small defects. The application of various topical agents has been described to allow gradual epithelialization of the sac. Staged reduction with a compressive dressing to encourage growth of the abdominal cavity may be appropriate.

Persistence of a patent processus vaginalis (related to testicular descent) is responsible for inguinal hernias and hydroceles in the neonate.

1. Inguinal hernia. The opening of the processus at the inguinal ring is large enough to allow abdominal viscera to extrude through the defect with increased intra-abdominal pressure.

2. Hydrocele. The patent processus is too narrow to permit egress of intestine. Peritoneal fluid leaves the abdominal cavity and accumulates in the processus vaginalis. Hydroceles are classified as communicating, if the processus remains patent, and noncommunicating, if the processus obliterates

1. Inguinal hernias tend to present as bulges at the pubic tubercle that continue along the inguinal canal. Less commonly, they descend into the scrotum.

2. Hydroceles are typically are found in the scrotum, transilluminate, and are not reducible

1. Inguinal hernias carry a 5–15% risk of incarceration during the first year of life. Usually, they are repaired surgically when the infant's general medical condition permits.

2. Hydroceles frequently resolve without intervention because the processus vaginalis continues to obliterate after birth. Hydroceles that persist beyond 6–12 months should be repaired.

An umbilical hernia is a skin-covered fascial defect at the umbilicus that allows protrusion of intra-abdominal contents.

Physical examination establishes the diagnosis.

During infancy, surgical intervention for an umbilical hernia is rarely warranted. Complications such as incarceration and skin breakdown are exceedingly rare. The natural history is one of gradual closure of the umbilical fascial defect, often leading to complete resolution. Surgical correction should be considered if the defect persists after the second birthday.