Gastroschisis

Prior to the 1960s, the outcome of infants born with holes in their abdominal wall (abdominal wall defects) was poor. The development of modern breathing machines for infants, nutrition that could be delivered directly into the blood, and man made synthetics that could act as a covering for the abdomen greatly improved the survival of these patients. Recently, the ability to diagnose these defects during pregnancy, further advances in the neonatal intensive care unit (NICU) management of infants, and the development of the modern operating room techniques and technology have led to most patients surviving.

The exact reasoning for the development of these defects is still unknown in many of these patients. However some abnormalities have a genetic basis to them. A table showing the difference between the two most common types of these defects, gastroschisis and omphalocele, is shown (Table 1).

Table 1. Clinical Findings in Infants with Abdominal Wall Defects

GASTROSCHISIS
Gastroschisis (Greek for “belly cleft”) is a defect of the abdominal wall almost always to the right of an intact umbilical cord (eventual belly button) (Figure 1 and 2).

This results in the intestines being located outside of the abdomen, and exposed to the air. Unlike omphalocele (covered later) there is no covering or “sac” over the intestines. A gastroschisis results in a large amount of intestine coming through a relatively small opening. When inside the mother, this intestine is exposed to the amniotic fluid (which contains fetal urine and various growth factors that are necessary for normal growth of the fetus).

However when the intestines are exposed to amniotic fluid, a chemical reaction occurs which is characterized by a thick film around the intestine. It is thought that this exposure contributes to the decrease function of the intestine for weeks to months after delivery in these patients. The exposed intestine appears matted and short. In addition, the intestine always fails to fall into its normal position and does not make its normal attachments to the back of the abdomen. In contrast to infants with omphalocele, associated problems are relatively rare in patients with gastroschisis. The exception is atresia (failure to form a segment of intestine) due to twisting, telescoping, or an interruption of the blood supply to a segment of exposed intestine (Figure 3) which occurs in 10% to 15% of patients.

The liver is almost never outside of the abdomen; the stomach, small bowel, and large intestine usually are outside of the hole. The bowel may be perforated (ruptured) in 5% of patients. Occasionally the ovaries and fallopian tubes in girls and an undescended testis in boys are found outside as well. The space in the abdominal cavity is often small. The sexes are equally affected. Most patients are born to young mothers; 25% are born to teenage mothers. Of patients, 40% are either premature or small for their gestational age. Gastroschisis is the most common of the abdominal wall defects. Occasionally there is a maternal history of a previous infant with gastroschisis. Chromosomal abnormalities almost never are encountered in infants with a gastroschisis.

Figure 4: Gastroschisis. A, Obstetric ultrasound at 34 weeks’ gestation shows dilated bowel (arrows) free in amniotic fluid adjacent to the umbilical cord insertion site. Previous ultrasounds at 27 and 31 weeks showed the bowel contained near the base of the cord, suggesting rupture of a small omphalocele (hernia of the cord) late in gestation. B, Typical gastroschisis after delivery at 35 weeks. Bowel edema and inflammation are minimal.

Gastroschisis frequently can be detected on a prenatal ultrasound study. The sonogram often shows dilated intestine free in amniotic fluid adjacent to the umbilical cord (Figure 4). When identified before birth, the pregnant woman should be referred to a high-risk obstetric unit with a neonatal intensive care unit and pediatric surgical expertise. Although delivering the baby early might theoretically minimize the irritating effect of the amniotic fluid upon the intestines, evidence does not suggest that early delivery improves the outcome. Spontaneous vaginal delivery is a reasonable choice for most of these infants.

When delivered, infants with gastroschisis may experience various problems as a result of the exposure of the intestine. Temperature loss, fluid loss, and infection are the major problems to avoid. The lower half of the infant (including the intestine) is placed into a sterile bowel bag, feet first, up to the level of the under-arms (Figure 5).

A tube is placed into the stomach through the mouth to remove swallowed air and gastrointestinal (stomach and intestinal) contents because the infant with gastroschisis almost invariably has difficulty moving air, fluid, and food normally through the intestines. The infant is given antibiotics and either has a preformed silo placed (Figure 6) or is taken to the operating room to close the hole in the abdomen.

Figure 7: The abdominal cavity is stretched manually in an attempt to increase the space in the abdomen for the bowel.

If going to the operating room, the infant is placed under well-monitored general anesthesia, the abdominal wall and exposed intestines are cleansed carefully with warm sterile saline and prepared with an anti-bacterial solution. The intestine is inspected carefully to make sure that all the intestine is alive and that there is no perforation or rupture of the intestine. The hole in the abdomen may initially need to be enlarged to allow the surgeon to put the intestines back into the abdomen (Figure 7).

The stomach and intestinal contents are aspirated through the tube previously placed through the nose or mouth into the stomach (NG tube), and the colon and rectum are evacuated through the anus by pressing on the intestines. Return of the intestine into the abdomen is attempted while monitoring chest and/or abdominal pressures. The intestines can be returned in more than 50% of patients. Often the umbilical cord stump can be preserved for cosmetic purposes to allow for a belly button (Figure 8). Alternatively, several surgeons create a belly button with a purse-string, circular suture during closure of the skin. After closure, most infants are maintained on the ventilator (breathing machine) for at least 24 to 48 hours.

Figure 8: A) The intestines are reduced (placed back into the abdomen). The hole in the muscle and skin will now be closed. Note the umbilical cord to the left of the hole in the abdomen. B) The remainder of the umbilical cord is included as part of the closure of the skin so that a belly button (umbilicus) is formed. Alternatively, a circular suture can be placed in the skin so that the skin is drawn down in the middle to form a belly button.

When closure is attempted immediately at birth, it may not be possible in 40% to 50% of cases. Too tight a closure may result in difficulty breathing from pressure on the diaphragm and decrease in blood supply going to the abdomen and returning from the abdomen, resulting in intestinal death. As such, some infants undergoing immediate closure of the gastroschisis will require placement of a “silo” in the operating room (Dacron-reinforced Silastic silo) as a temporary housing for the intestines. This either comes preformed (Figure 6) or needs to be fashioned by the surgeon (Figure 9).

The upper end of the silo is tied with umbilical tape, which is suspended loosely over the infant. An antibiotic ointment is placed around the base of the silo at the skin to prevent infection. The intestines can be returned to the abdomen gradually by gentle pressure and placing the string which ties off the top of the silo gradually lower on the silo at the bedside in the NICU. Once the intestines are almost all back inside, the silo is removed and the hole in the abdomen closed. This process is usually completed within 1 to 3 weeks in most cases. The infant is returned to the operating room for closure of the gastroschisis. Antibiotics are discontinued shortly after the silo is removed.

Articles and graphics adapted from O'Neill: Principles of Pediatric Surgery. © 2003, Elsevier.