Congenital Abdominal Wall Defects: Gastroschisis and Omphalocele

Incidence, Embryology, and Etiology

Gastroschisis occurs in 1 in 4000 live births. An increased incidence in mothers younger than 21 years of age has been widely documented, although the reasons leading to the rising numbers are unclear. There has been a significant worldwide increase in the incidence of gastroschisis in all maternal age groups over the past two decades. Preterm delivery is more frequent in infants with gastroschisis, with an incidence of 28% compared with only 6% in babies without an abdominal wall defect.

The abdominal wall forms during the fourth week of gestation when differential growth of the embryo causes infolding in the craniocaudal and mediolateral directions. During the sixth week, rapid intestinal and liver growth leads to herniation of the midgut into the umbilical cord. Elongation and rotation of the midgut occurs over the ensuing 4 weeks. By week 10, the midgut returns to the abdominal cavity, where the first, second, and third portions of the duodenum and the ascending and descending colon assume their fixed, retroperitoneal positions. At the most basic level, an abdominal wall defect involves an interruption of these embryologic processes and results in abnormal development. One theory suggests that gastroschisis results from failure of the mesoderm to form in the anterior abdominal wall. Currently, the ventral body folds theory, which suggests failure of migration of the lateral folds (more frequent on the right side), is most widely accepted. This implies that a gastroschisis develops early in gestation and before an omphalocele might develop.

There are a variety of potential agents that have been implicated in the development of gastroschisis; however, no specific causal relationship has been established. A number of possible causative factors, including tobacco, certain environmental exposures (nitrosamines), cyclooxygenase inhibitor use (aspirin and ibuprofen), and decongestants (pseudoephedrine and phenylpropanolamine), have been suggested as etiologic agents. The well-known association of lower maternal age and low socioeconomic status with a higher incidence of gastroschisis has been linked with violence against women during gestation as a potential factor. Other factors such as change in paternity for gestations also have been suggested.

Presentation and Diagnosis

Most pregnancies complicated by gastroschisis are diagnosed sonographically by 20 weeks’ gestation. Routine ultrasonography (US) often suggests the abnormality that is confirmed on a higher level US. Often US is performed because of an abnormal maternal serum α-fetoprotein (AFP) level, which is universally elevated in the presence of gastroschisis. Detection of bowel loops freely floating in the amniotic fluid and a defect in the abdominal wall to the right of a normal umbilical cord are diagnostic of gastroschisis. Intrauterine growth restriction (IUGR) has been noted in a large number of these fetuses. Some fetuses with gastroschisis are not diagnosed prenatally and are discovered at the time of delivery, which can result in challenges with neonatal management. These neonates must be transferred to a center with the ability to care for gastroschisis. Fortunately the incidence of previously unknown gastroschisis at delivery is becoming rare with improved prenatal care. Data regarding outcomes of gastroschisis with inborn versus outborn babies does not suggest a worse outcome for either group.

Prenatal Management and Delivery

The ideal prenatal test would be able to accurately differentiate gastroschisis fetuses at risk for complications such as intestinal loss or closing defects. Despite extensive use of US in fetal gastroschisis and the identification of multiple potential predictors of an adverse outcome (such as complex gastroschisis), there is no consensus on their use in selecting fetuses for early delivery. Factors that maternal-fetal medicine experts consider important for gastroschisis are intra-abdominal bowel dilation, bowel wall thickening, gastric dilation, IUGR, polyhydramnios, liver herniation, urinary bladder herniation, and changes in bowel dilation over the gestation. Two systematic reviews/meta-analyses looked at the accumulated studies on prenatal indicators and risk factors in gastroschisis, noting the same predictors listed earlier. Both reviews concluded that although in some cases a combination of two or more indicators may be used to identify fetuses at risk for complications, there was no reliable factor, and much discrepancy existed between centers and experts regarding the exact definition of normal and abnormal. These indicators were not able to accurately predict who would benefit from early delivery, and large prospective studies were advocated.

Gastroschisis is associated with a variable degree of inflammatory thickening of the visceral bowel walls, which results in the characteristic appearance of “matted” intestinal loops. The reason for this inflammatory “peel” is unclear, but the presence of elevated levels of cytokines (interleukin-6 [IL-6], IL-8, tumor necrosis factor [TNF]-α) in the amniotic fluid, in addition to the effects of fetal urine, is thought to cause the abnormal collagen deposition. One report noted a significant decrease in interstitial cells of Cajal (ICCs) in gastroschisis bowel in neonates compared with controls, further implicating the role of the proinflammatory state in utero. Studies in animal models have shown that the duration of amniotic fluid exposure is correlated with the degree of the inflammatory peel and intestinal dysmotility. Efforts to reduce this exposure by either amniotic fluid exchange or intrauterine furosemide treatment, which induces fetal diuresis, have shown to be beneficial in animals. These animal studies spurred early human trials with amniotic fluid exchange in Paris and Italy, but these trials have proven inconclusive and are not being performed in humans at this time.

The optimal mode and timing of delivery for a fetus with gastroschisis has been debated for many years. Proponents of routine cesarean delivery (C-section) argue that the process of vaginal birth results in injury or increased risks for infection and sepsis. However, the literature suggests that both vaginal delivery and C-section are safe. A meta-analysis failed to demonstrate a difference in outcomes for infants delivered either vaginally or by C-section. Therefore, the delivery method should be at the discretion of the obstetrician and the mother, with C-section reserved for obstetric indications or fetal distress.

Preterm delivery of the fetus with gastroschisis has been advocated to limit exposure of the bowel to the amniotic fluid. Damage to the pacemaker cells and nerve plexi may contribute to the profound dysmotility and malabsorption seen in these infants. Early delivery may theoretically mitigate these effects, but the data are increasingly against preterm delivery. Although a number of single-center retrospective studies have suggested that elective preterm delivery before 37 weeks’ gestation is beneficial and have reported an earlier time to attaining full enteral feeds and a decreased length of stay, these investigators also utilized a care pathway that may have been responsible for the improved outcomes. Grant et al. noted in a 2013 Cochrane review of preterm birth for gastroschisis that there was not enough evidence to suggest a beneficial effect. Two overlapping reports from Toronto noted that early delivery was associated with a higher complication rate and planning induction at 37 weeks was better than expectant management. A report from the Canadian Pediatric Surgery Network (CAPSNet) noted a linear relationship between increasing gestational age and decreasing bowel matting, and strongly advocated delivery at term (defined as 37 weeks). A randomized trial from the United Kingdom found no benefit after induced early delivery, with the only trends being an improvement in length of hospitalization and earlier initiation of feeding. Another study demonstrated that birth weight less than 2 kg was associated with increased morbidity. Currently available evidence does not support the practice of elective preterm delivery for gastroschisis.

Neonatal Resuscitation

Neonates with gastroschisis have significant evaporative water losses from the open abdominal cavity and exposed bowel. Appropriate intravenous access should be obtained and fluid resuscitation initiated after birth. Nasogastric (NG) decompression is important to prevent further gastric and intestinal distention. Routine endotracheal intubation is not necessary. The bowel should be wrapped in warm saline-soaked gauze and placed in a central position on the abdominal wall. The neonate should be positioned on the right side to prevent kinking of the mesentery with resultant bowel ischemia. Viscera are covered by a plastic wrap or the infant is placed partially in a plastic bag (“bowel bag”) to reduce evaporative losses and improve temperature homeostasis ( Fig. 48.2 ). Although gastroschisis most often is an isolated anomaly, thorough examination of the neonate is important. Concomitant bowel atresia is the most common associated anomaly in patients with gastroschisis, with rates ranging from 7–28% in several series ( Table 48.2 ). A review of the literature noted rare occurrences of associated anomalies in the cardiac, pulmonary, nervous, musculoskeletal, and genitourinary systems, as well as chromosomal abnormalities in babies with gastroschisis. Additional evidence suggests that excess fluid resuscitation is detrimental and results in edema, an increase in time to closure, and an increased risk of abdominal compartment syndrome.

Risk Stratification

Over the course of the last two decades, realization that there was a subset of gastroschisis neonates that were at higher risk for morbidity and mortality has led to the development of risk stratification. This risk was based on the presence or absence of any intestinal complication (atresia, ischemia, perforation, or development of necrotizing enterocolitis [NEC]) and could be classified as complex or simple gastroschisis ( Figs. 48.3 and 48.4 ). Patients with complex defects have a higher mortality rate, require multiple operative interventions, and have a prolonged hospitalization, increased rates of sepsis, and higher rates of prolonged cholestasis and need for intestinal transplantation due to intestinal failure. This definition and an improved understanding have allowed better parental counseling, hospital planning, and transfers to centers with advanced capabilities to care for complex patients. In addition, this classification allows for an improved ability to compare treatments—for example, simple versus complex defects—and remove the variability associated with the complex patients.

Surgical Management

The primary goal is to expeditiously return the viscera to the abdominal cavity while minimizing the risk of damage due to intestinal injury or increased intra-abdominal pressure. The two main treatment options are primary repair and delayed closure with use of a temporary silo and serial reduction. In all cases, inspection of the bowel for obstructing bands, perforation, or atresia should be undertaken. Bands crossing the bowel loops should be lysed before silo placement or primary abdominal closure to avoid potential subsequent intestinal obstruction. The choice of which course to undertake is dependent on the presentation of the bowel, as well as surgeon and institution preferences, and is both variable and controversial.

Primary Closure

Historically, urgent primary closure of gastroschisis was advocated in all cases, and in the situation in which this was not possible, the neonate would not survive. This approach is still commonly practiced in neonates in whom reduction of the herniated viscera is feasible, but has diminished with the use of the preformed silo. Attempted primary closure is usually performed in the operating room under general anesthesia, but some surgeons have advocated primary closure at the bedside without anesthesia. Some surgeons prefer to close the skin only and leave the fascia separated. Others have described the use of the umbilicus as an allograft. A prospective randomized study comparing sutureless closure to sutured repair noted that the time to full feeds and length of stay was significantly longer in the sutureless group, despite no additional complications. Youssef et al. performed a systematic review and meta-analysis of flap versus fascial closure, and found that flap repair was associated with equivalent or superior outcomes to fascial closure. Prosthetic options for fascial closure include nonabsorbable mesh or bioprosthetic materials such as porcine small intestinal submucosal mesh. In the past, most surgeons have excised the umbilicus during closure; however, preservation of the umbilicus has been shown to lead to an excellent cosmetic result. Therefore, most surgeons will now try to save it ( Fig. 48.5 ).

Intra-abdominal pressure measured by either the bladder or stomach pressure has been used to guide the surgeon during reduction. Pressures higher than 10–15 mmHg are often associated with decreased renal and intestinal perfusion, and a silo or patch may be needed, whereas above 20 mmHg they correlate with organ dysfunction and complications. Similarly, an increase in central venous pressure greater than 4 mmHg has been correlated with the need for silo placement or patch closure. Splanchnic perfusion pressure, the difference between mean arterial pressure and intra-abdominal pressure, also has been used to guide the reduction. A splanchnic perfusion pressure less than 44 mmHg implies a decrease in intestinal blood flow.

A prospective randomized trial comparing silo versus immediate closure noted a significantly reduced time on the ventilator with no other differences between the groups. This study was underpowered as it did not meet accrual numbers. However, another prospective analysis is being performed and the results are pending.