Omphalocele
An omphalocele, or exomphalos, is a midline abdominal wall defect covered by a membrane of amnion and peritoneum containing bowel, and, occasionally, spleen and liver at the base of the umbilical cord. When the defect is less than 4 cm, it is termed a hernia of the umbilical cord; when it is greater than 10 cm, it is termed a giant omphalocele. It results from the persistence of the physiologic midgut herniation beyond the 12th postmenstrual week. Associated abnormalities occur in 30% to 70% of infants and include chromosomal abnormalities (trisomy 13, 18, 21), congenital heart disease, Beckwith- Wiedemann syndrome, and prune belly syndrome. The diagnosis of an omphalocele can usually be made by inspection, but if the omphalocele is small, it may appear to be a normal part of the umbilical cord. The major differential diagnosis to consider is gastroschisis. Gastroschisis is a defect in the abdominal wall that usually occurs to the right of the normal insertion area of the umbilical cord; it is believed to arise at the site of involution of the right umbilical vein. The absence of a membranous sac with free-floating loops of bowel distinguishes gastroschisis from omphalocele; if the membranous sac of the omphalocele ruptures in utero, however, other clues should be sought, such as the location of the liver and site of the cord insertion. When omphalocele is identified prenatally, fetal genetic studies, including amniocentesis and fetal echocardiography, should be offered because of the high risk of aneuploidy and other congenital and genetic disorders. Fetal growth should subsequently be monitored closely. Precluding other obstetric indications, spontaneous labor and delivery should be allowed to occur.
However,
referral to a tertiary care center is highly recommended.
In
the delivery room, neonatal management involves covering the defect with gauze
dressings soaked in thermally neutral sterile saline, covering the dressing
with clear plastic wrap, inserting an orogastric tube to decompress the
stomach, stabilizing the airway to ensure adequate ventilation, and
establishing peripheral intravenous access. The primary goal of surgery is to
return the viscera to the abdominal cavity and close the defect; with an intact
sac, emergency operation is not necessary, however. Small defects (<2 cm)
can generally be managed by primary direct closure, whereas medium to large
defects require a staged procedure.
A
staged repair aims to create a protective extraabdominal extension of the
peritoneal cavity (termed a silo), allowing gradual reduction of the
viscera and gradual abdominal wall expansion. This is achieved by using two
parallel sheets of reinforced Silastic sheeting sutured to the fascial edges or
a preformed one-piece silo with a collapsible ring at its base for ease of
insertion. A prosthetic patch repair bridges the fascial gap with a synthetic
material (e.g., polytetrafluoroethylene), and the skin is closed over the
patch. The silo is progressively compressed to invert the amniotic sac and its
contents into the abdomen and to bring the edges of the linea alba together by
stretching the abdominal wall muscles. This usually requires 5 to 7 days, after
which the defect is primarily closed. The intraabdominal pressure produced by
the silo should not exceed 20 cm of water to avoid impairing venous return from
the bowel and kidneys. When abdominal relaxation
is sufficient to allow the rectus muscles to come together, the silo is
removed, the amnion is left inverted into the abdominal cavity, and the defect
is closed.
Management
of an omphalocele may be complicated by rupture of the omphalocele sac either
in utero or during delivery. The frequency of multiple congenital anomalies in
these infants must also be borne in mind. Some variety of intestinal
obstruction is common, especially anomalies of rotation and fixation of the
colon.
Obviously,
if intestinal obstruction is suspected from x-ray studies or other signs, such
as vomiting, failure to pass a stool, or distention, the proper corrective
intraabdominal procedure must be undertaken before the closure is completed.
The survival rate for infants with small omphaloceles is excellent. The overall survival rate is 90%. Death is associated with wound dehiscence in larger omphaloceles, with subsequent infection, or with associated anomalies.
