Part F: Gastro-Intestinal

Management of Abdominal Wall Defects

DIAGNOSIS

Omphalocele and gastroschisis represent the 2 most frequently encountered abdominal wall defects requiring neonatal intensive care. As discussed previously in this book, these defects occur in roughly 1–3 per 10,000 live births. Although the incidence of omphalocele has remained constant in recent years, the incidence of gastroschisis has been increasing for unclear reasons.

Clinical Findings

Omphalocele is associated with advanced maternal age and karyotype abnormalities; gastroschisis is associated with maternal age less than 20, smoking, and use of over-the-counter vasoactive drugs and salicylates during pregnancy.^{1, 2, and 3} In addition, illicit drug abuse and smoking may influence the severity of gastroschisis.⁴

Omphalocele is characterized by the failure of the viscera to return to the abdominal cavity following physiologic midgut herniation during the 10th week of gestation. As a result, the omphalocele is contained within a protective membranous sac composed of amniotic epithelium lined by peritoneum, with the intervening space filled by Wharton’s jelly. The stomach, small bowel, colon, and liver are frequently involved. Associated anomalies occur in 50%–70% of infants with omphalocele; cardiac defects are observed in 30%–50%. Karyotype abnormalities occur in 30% of cases, with trisomies 13, 18, and 21 most common.²

Gastroschisis, on the other hand, is characterized by prenatal evisceration through a defect in the anterior abdominal wall, almost always located just to the right of the umbilicus. This right-sided predilection is theorized to be caused by abnormal embryonic regression of the right umbilical vein. Importantly, the eviscerated abdominal contents do not have a protective membrane and are in direct contact with the amniotic fluid. The involved intestine is edematous, sometimes foreshortened, and almost always nonrotated. Of neonates with gastroschisis, 7%–10% will have an associated intestinal atresia. Unlike omphalocele, gastroschisis is not associated with karyotype abnormalities.²

The effective management of both omphalocele and gastroschisis hinges on early diagnosis and the involvement of appropriately trained staff (trained nurses, neonatologist, and pediatric surgeons). The embryologic and anatomic differences, however, lead to the differences in management depicted in the discussion that follows.

Confirmatory (Diagnostic) Tests

Prenatal Imaging

The sensitivity and specificity of prenatal ultrasound in identifying abdominal wall defects are 60%–75% and 95%, respectively.^5,6 Once a fetus with an abdominal wall defect is identified, directed ultrasounds should be performed to look for associated anomalies and malformations. Fetal magnetic resonance imaging is gaining popularity and is now used as a reflex imaging study if initial ultrasound is suspicious for gastroschisis or omphalocele in many centers.

Laboratory Tests

There is a marked elevation of maternal serum α-fetoprotein (AFP) in cases of gastroschisis; omphalocele tends to have a more modest AFP elevation (7–9 multiples of the mean compared to 4 multiples of the ...