Abdominal wall defects

							A baby born with an abdominal wall defect presents a management challenge to the pediatric surgeon
and NICU team. The outlook for such patients was poor prior to 1960 due to the lack of mechanical
ventilators for infants and the inability to maintain adequate nutrition during the prolonged
postoperative adynamic ileus. The 1960s brought several signal developments, including the "silo"
method of abdominal wall closure, infant ventilators, and total parenteral nutrition (TPN). Further
recent advancements include the ability to make an antenatal diagnosis by ultrasonography and
improvements in OR and NICU monitoring and care. The prognosis for the majority of neonates with
abdominal wall defects now, barring other life-threatening congenital anomalies, is quite good.



An omphalocele is a central sac-covered defect related to the umbilical ring and abnormalities of the
embryonic abdominal wall folds. Incomplete lateral wall infolding produces a central omphalocele while
problems with the cephalic and caudal folds produce epigastric or hypogastric omphaloceles,
respectively. The sac is composed of an inner layer of peritoneum and an outer layer of amnion with
Wharton's jelly in between. The umbilical cord inserts onto the sac, and the umbilical vessels are splayed
out across it. Rupture of the sac may occur in 10% to 18% of cases antenatally and in 4% at the time of
delivery. The abdominal wall defect measures 4 cm or more in diameter, and the herniated viscera
include multiple loops of bowel, part of the stomach, and often a portion of the liver (a defect
measuring less than 4 cm in diameter is defined as a congenital hernia of the umbilical cord, usually
contains only a few loops of intestine, and is easily dealt with). Boys are more commonly affected than
girls, and many patients are born prematurely. More than half of omphalocele patients have other
congenital anomalies. Associated syndromes include upper midline fusion (Cantrell's pentalogy), lower
midline fusion (cloacal exstrophy), Beckwith-Wiedemann, Reiger's, prune-belly, and trisomies 13, 14, 15,
18, and 21. Congenital heart disease occurs in 15% of patients, but only 1% have GI tract anomalies.



A gastroschisis is an open (ie, no sac) defect usually situated to the right side of a normally inserting
umbilical cord. The embryogenesis of this defect is really unproven. The hole in the abdominal wall is
usually fairly small, but most of the small and large intestine is eviscerated through it; stomach and
ovaries and tubes or undescended testes are also sometimes found. The exposed bowel is thickened,
matted together, and foreshortened due to chemical peritonitis form exposure to amniotic fluid and/or
venous congestion from constriction of a tight defect about the bowel mesentery. Gastroschisis occurs 2
to 3 times more commonly than omphalocele. The sexes are equally affected, and 40% of cases are born
prematurely or SGA. As opposed to omphalocele cases, GI tract anomalies, especially intestinal atresias,
occur more frequently in gastroschisis patients (15%), but other congenital anomalies are rare.



With good antepartum obstetric management, most abdominal wall defect cases these days are
diagnosed in utero. A marked elevation in maternal serum alpha fetoprotein (AFP) occurs in both
omphalocele and gastroschisis and may be the first tipoff to the diagnosis. Ultrasonography can also
detect an abdominal wall defect as early as the first trimester. It can be used to differentiate the type of
defect, to look for other anomalies, and in a serial fashion to monitor the defect and fetal growth. As the
pediatric surgeon, I like to meet with the expectant parents along with the neonatologist. We discuss
the implications of the diagnosis and describe the management of the baby after birth. We also have the
nurses take the parents on a tour of the NICU. The biggest advantage of antenatal diagnosis is to allow
delivery of the baby in a high-risk center such as St. Mary's Hospital with a high level NICU and pediatric
surgery and neonatology expertise.



The choice of mode of delivery with abdominal wall defects is controversial. With vaginal delivery,
instances of liver injury with omphalocele and catastrophic intestinal loss and bleeding due to
mesenteric tears with gastroschisis have occasionally occurred. My own recommendation, being on the
receiving end of the baby, is C-section. However, several reports describing large modern series show no
clear advantage to C-section over vaginal delivery.



If possible, it is helpful for both the pediatric surgeon and the neonatologist to attend the delivery. As
soon as the baby is handed off, I examine the abdomen to confirm the type of defect and determine the
status of the bowel. I then apply sterile saline-soaked 4"x4" gauze sponges to the sac/viscera & wrap the
baby circumferentially with Kerlix and Kling to keep the viscera centered over the anterior abdomen. An
orogastric tube is placed to evacuate swallowed air and keep the stomach and intestines of as small
volume as possible. Much fluid is lost from the peritoneal cavity across an open defect such as a
gastroschisis or ruptured omphalocele, so isotonic IV fluids +/- colloid should be vigorously
administered. Heat loss can also be significant, so the baby should be kept warm with warm blankets in
transport or a radiant warmer bed in the nursery. Broad-spectrum antibiotics (ampicillin and gentamicin
or ampicillin and cefotaxime) are begun.



Viscero-abdominal disproportion, or a small abdominal cavity relative to the amount of viscera that
need to fit in it, is a surgical challenge. The goal of operation is to reduce the herniated viscera and close
the abdominal wall without compromising the baby's respiratory state, hemodynamics, or intestinal
blood supply. If everything fits without undue intra-abdominal pressure, the abdomen is closed
primarily. During the closure, the surgeon maintains a dialogue with the anesthesiologist about the
baby's oxygenation, ventilatory pressures, and hemodynamics. If a primary repair cannot be achieved, a
prosthetic "silo" is created to contain the viscera. The "silo" is then serially reduced in the NICU as the
abdominal wall stretches until the "silo" can be removed and the abdomen formally closed, generally in
5 to 10 days. At the initial operation, I also place a tunnelled long-term Silastic (eg, Broviac) central
venous line (CVL) for postoperative central TPN and an umbilical artery catheter (UAC) for blood
pressure and ABG monitoring.
Postoperatively, especially with a primary abdominal repair, the baby may need continued endotracheal
intubation and mechanical ventilation, possibly with sedation and muscle relaxation. The patient is
closely monitored, and cardiopulmonary compromise or increasing metabolic acidosis due to high intra-
abdominal pressure would mandate conversion of a primary to a "silo" repair. As the abdominal wall
tension relaxes, the baby can be weaned from the ventilator and extubated. The patient is kept NPO and
the stomach decompressed with an orogastric tube until the adynamic ileus resolves which may take
anywhere from a few days to weeks. Nutrition is provided as TPN until enteral feedings can be
established. Antibiotics are continued for 7 to 10 days following definitive abdominal closure.



The prognosis for babies born with abdominal wall defects these days is good. Gastroschisis carries a
survival rate of over 90%. The survival rate for omphalocele patients is a bit less due to the increased
incidence of other anomalies.



We have treated 15 neonates with abdominal wall defects at St. Mary's Hospital from 1996 to 2006, 13
with gastroschisis, 1 with omphalocele, and 1 with antenatal rupture of a hernia of the umbilical cord.
Twelve babies were diagnosed antenatally and were born in-house, and 3 patients were discovered at
birth elsewhere and transported to us. There were 11 C-sections and 4 vaginal deliveries with no birth
injuries. A primary abdominal repair was achieved in 14 patients, and 1 patient required a temporary
"silo" for 7 days. The mean time to endotracheal extubation was 1.7 postoperative days. The median