Management of Abdominal Wall Defects

               Zachary Kastenberg and Matias Bruzoni

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.^1–3 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 mean, respectively).^7,8 As discussed previously in another chapter, a positive ultrasound or a significant elevation of maternal serum AFP should lead to a discussion regarding possible amniocentesis or chorionic villus sampling to identify significant chromosomal abnormalities.

Differential Diagnosis

Umbilical Hernia

Umbilical hernias are differentiated from gastroschisis and omphalocele by the presence of normal skin overlying the defect. They contain easily reducible omentum or intestine. Repair is not undertaken in the neonatal period unless incarceration is present as nearly 90% of these defects close spontaneously by 3 to 4 years of age.⁹

Prune Belly Syndrome

Prune belly (Eagle-Barrett) syndrome consists of deficiency or absence of abdominal wall musculature; a constellation of ureteral, bladder, and urethral anomalies; and bilateral cryptorchidism. Prune belly syndrome is distinguished from other abdominal wall defects by complete containment of the abdominal viscera within a continuous layer of skin with a normal umbilicus. In most cases, the lack of abdominal musculature does not cause significant functional impairment.

Megacystis-Microcolon

Megacystis-microcolon is a rare congenital anomaly resulting in a massively distended, nonobstructed bladder and a secondary microcolon, often with associated hypoperistalsis and small-bowel malrotation.¹⁰ The components of the abdominal wall are present and intact, but the abdomen is massively dilated secondary to the mass effect of the dilated bladder. Diagnosis is typically made by preoperative ultrasound, and initial treatment consists of transurethral bladder drainage. The underlying etiology is poorly understood, and the condition is generally not survivable as a result of the severely dysfunctional and underdeveloped gastrointestinal tract.

PRETREATMENT

Ethical Considerations

Advances in neonatal intensive care and surgical technique have made both gastroschisis in the absence of abdominal catastrophe and isolated omphalocele survivable conditions with little to no long-term morbidity. If however, severe associated anomalies are identified on prenatal imaging or if a significant karyotype abnormality exists, the likelihood of long-term survival is dramatically reduced. A discussion with the parents is necessary to explain the possible outcomes and options, including, if appropriate, pregnancy termination.

Monitoring for Treatment/Procedure/Workup

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