Gastroschisis Versus Omphalocele / Exomphalos
Author:
Junise Swanson RN
Jonathan Weeks, M.D.
Objectives: Upon the completion of this CME article, the reader will be able to
1.
Explain the importance of making a distinction between a diagnosis of gastroschisis
versus omphalocele.
2.
Describe the associated anomalies that can be seen with gastroschisis and
omphalocele.
3.
Discuss the overall prognosis and management of gastroschisis and omphalocele.
Introduction
There are two main types of ventral abdominal wall defects seen at the level of the
umbilicus that are detectable by perinatal ultrasound. These are gastroschisis and
omphalocele / exomphalos. The identification of these two anomalies by ultrasound along
with being able to differentiate between them is essential for prenatal diagnosis, obstetrical
management, and assessing prognosis.
Definition and Incidence
Gastroschisis is a malformation of the abdominal wall that presents as a protrusion
of viscera through a paraumbilical defect. This condition has no known genetic association.
The defect usually occurs to the right of the umbilicus but the umbilicus is intact.
Gastroschisis involves all the layers of the abdominal wall. As a result, the small bowel
almost always eviscerates through the defect and floats freely in the amniotic fluid. There is
no membranous covering. It is also unusual for the liver, spleen, or bladder to herniate
through the defect. The incidence of gastroschisis worldwide is about 1 per 10,000 live
births. However, isolated cases of gastroschisis can occur at a rate of about 7 per 10,000 live
births in mothers under the age of 20.
Omphalocele (Exomphalos) is a midline defect where the abdominal contents
herniate through the base of the umbilicus. The herniated abdominal contents usually
include the bowel and stomach, and often a portion of the liver. These contents are covered
with a translucent, avascular membrane, consisting of peritoneum on the inside and amniotic
membrane on the outside, separated by Wharton’s jelly. The incidence of omphalocele in
live births worldwide is about 2 per 10,000 and increases with maternal age.
Pathogenesis
Gastroschisis is a defect resulting from a vascular compromise of either the right
umbilical vein or the omphalomesenteric artery. Disappearance of the right umbilical vein
(prior to 28-32 days after conception) may lead to ischemia and result in mesodermal and
ectodermal damage. Another possibility is a vascular accident involving the
omphalomesenteric artery that leads to a disruption of the umbilical ring and hence,
herniation of the abdominal contents.
The pathogenesis of Omphalocele / Exomphalos is completely different. During
the development of the embryo, four areas of tissue converge to complete the closing of the
abdominal wall. These are the caudal (lower), cephalic (upper), and two lateral (side) folds.
If the caudal (lower) fold fails to fuse, it results in cloacal extrophy of the bladder. If the
cephalic (upper) fold fails to fuse the result is omphalocele with ectopia cordis (the fetal
heart outside the chest) along with sternal and / or diaphragmatic malformations (often
called Pentalogy of Cantrell). When the lateral (side) folds fail to fuse, this results in isolated
omphalocele producing the herniation of bowel and usually liver, stomach, and sometimes
spleen depending on the size of the defect. This herniation is contained within a
membranous sac into which the umbilical cord inserts.
Associated Anomalies
Approximately 80% of gastroschisis cases are isolated occurrences, but 10% to 30%
are associated with other malformations. Intestinal tract complications are the most
common and include malrotation, atresia, stenosis, chemical irritation and thickening (due to
direct exposure with the amniotic fluid), ischemia of bowel sections (due to kinking), and
bowel obstruction. Other defects or complications that have been reported are congenital
heart defects, hydrocephalus, polyhydramnios, oligohydramnios, genitourinary tract
abnormalities, and prune belly syndrome.
For omphalocele / exomphalos, approximately 50% to 70% are associated with
other serious anomalies. Chromosome abnormalities are seen in about 50% of the fetuses
with omphalocele. (To briefly review, the normal genetic makeup of an individual should
consist of 22 pairs of chromosomes, which are numbered 1 through 22, with a pair of sex
chromosomes, for a total of 23 pairs or 46 chromosomes.) The most common chromosome
anomalies seen with omphalocele are trisomy 13, trisomy 18, and trisomy 21. Other
chromosome abnormalities include Turner Syndrome (a female with the genetic makeup of
45 chromosomes but only one X chromosome – 45 XO), Klinefelter Syndrome (a male with
more than one X chromosome – most often 47 XXY), and triploidy (which is an individual
with a complete set of 23 extra chromosomes – such as 69 XXX). Other sporadic disorders
that may include omphalocele as a component are Pentalogy of Cantrell (as described above)
and Beckwith-Wiedemann syndrome (which is a disorder of macrosomia in conjunction with
an enlarged liver and kidneys and a large protuberant tongue – macroglossia). Associated
cardiac defects are also common (such as ventricular septal defect and tetralogy of Fallot) as
are neural tube defects, a two-vessel umbilical cord, diaphragmatic hernias, arteriovenous
(AV) malformations, low birth weight, and a higher incidence of preterm delivery.
Ultrasound Findings and Prenatal Diagnosis
For gastroschisis, multiple echogenic free-floating bowel loops near the anterior
abdominal wall can be visualized during an ultrasound evaluation. A membranous covering
or sac will not be seen. There will also be an intact umbilical cord insertion site seen to the
left of the defect. Polyhydramnios or oligohydramnios can also be present. These findings
can be identified on a routine ultrasound; however, a targeted scan should be done to
evaluate the fetal anatomy for other possible anomalies. Early detection of additional
anomalies might affect prognosis. Factors that can sometimes make it difficult to identify
gastroschisis are a low amount of amniotic fluid (oligohydramnios), the size of the defect,
the fetal size and gestational age, and the fetal position. Detection before 12 weeks gestation
can be difficult due to the normal migration of the fetal gastrointestinal tract. The
embryonic bowel normally protrudes into the base of the umbilical cord during the first
trimester of pregnancy. The bowel later migrates back into the abdominal cavity. This
process occurs between the 8th and 12th week of gestation. Therefore, it is important not to
make an incorrect diagnosis of a fetal anomaly at this early gestational age for a finding that
is a normal anatomical process.
The maternal serum alpha-fetoprotein (MSAFP) is a screening genetic blood test that
can be performed during pregnancy. Values are recorded as abnormally low, normal, or
abnormally high. For gastroschisis, the MSAFP level is abnormally elevated in 98% of the
cases. If an amniocentesis is performed, the amniotic fluid AFP level is also elevated.
Acetylcholinesterase (ACHE) is another substance that can be tested for in amniotic fluid.
Under normal circumstances, ACHE should not be detected in the amniotic fluid.
However, for gastroschisis, ACHE is detected in the amniotic fluid. If you combine MSAFP
screening with a positive identification by ultrasound, most cases of gastroschisis can be
diagnosed prenatally (figures 1 & 2).
For omphalocele / exomphalos, a solid appearing, round, echogenic mass adjacent
to the anterior abdominal wall is seen on ultrasound. The herniation is in the midline within
a sac or membrane and the umbilical cord inserts into this mass. Amniotic fluid AFP levels
are also usually significantly elevated (similar to gastroschisis). As with gastroschisis, by
combining AFP screening with a positive identification by ultrasound, a diagnosis of
omphalocele can usually be made. With this diagnosis, however, a targeted scan for other
abnormalities is very important due to the high rate of associated anomalies (figures 3 & 4).
Management and Prognosis
Proper management of the infant diagnosed with an abdominal wall defect is
important in terms of:
1.
Detecting associated anomalies early
2.
Delivering the child at a center where appropriate postnatal care can be
performed
3.
Preventing iatrogenic injury to the herniated abdominal contents during
delivery, and
4.
Determining the proper delivery time as to decrease bowel damage in utero
With a diagnosis of gastroschisis, the fetus should have follow-up ultrasounds to
watch for intrauterine growth restriction (seen in 50% of cases), oligohydramnios or
polyhydramnios, and for signs of bowel obstruction and damage. Karyotyping (genetic
amniocentesis) is not usually recommended because most cases of gastroschisis are not
associated with chromosome abnormalities. (One potential concern, however, is the issue
that an omphalocele that has ruptured through its membrane covering could mimic a
gastroschisis. Therefore, some prenatal testing centers may offer further genetic testing.)
Most studies have concluded that cesarean section does not significantly benefit the fetus
regarding morbidity and mortality postnatally. If the defect is large and contains a portion of
the liver, most obstetricians would consider cesarean section over vaginal delivery. If at all
possible, the child should be delivered at a tertiary care center. In the case of an isolated
gastroschisis the overall prognosis is very good with a survival rate of greater than 90%. In
cases where a significant atresia of the intestinal tract has occurred, the survival rate can drop
to as low as 40%. Usually the gastroschisis will be closed within 24 hours of delivery.
Staged closures may be necessary depending on the size of the defect and associated
anomalies.
For omphalocele / exomphalos, serial ultrasound evaluations are indicated to follow
fetal growth. Intrauterine growth restriction is also common with this disorder, along with
polyhydramnios and preterm labor. Rupture of the membrane covering is rare (but can
occur); however, bowel atresias are uncommon. Karyotyping (through genetic
amniocentesis) is usually recommended, especially in the presence of other anomalies
because of the high rate of chromosomal abnormalities seen with omphalocele. An
omphalocele by itself is not an indication for cesarean section. For a large omphalocele
containing liver, the fear of injury to the liver with vaginal delivery is a concern and
therefore, cesarean section is often recommended. Stillbirths are common among fetuses
with omphalocele, especially in the presence of other anomalies or chromosomal defects.
Death during the neonatal period depends on the other anomalies that may be seen in
addition to the omphalocele. Severe associated anomalies are responsible for 80% to 100%
of the reported deaths. Sepsis and complications from surgical repairs are responsible for
less than 10% of the deaths. Approximately, 50% of fetuses diagnosed with omphalocele
will not survive (again, this is usually due to the other associated abnormalities). In the
absence of other anomalies, the outcome for a fetus with omphalocele is good. Surgical
repairs can be complex and staged closures are usually dependent upon the size of the
defect. Omphaloceles are usually repaired within 24 to 48 hours of birth.
Summary
Though somewhat similar in their presentation (an abdominal wall defect with an
elevated maternal serum AFP level), gastroschisis and omphalocele are distinctly different.
They have a dissimilar pathogenesis and can carry a different prognosis depending on the
associated anomalies, if present. It is important for ultrasonographers to understand these
differences when dealing with a patient who is carrying a fetus with one of these congenital
defects.
Figures
1&2
Gastroschisis – free-floating bowel loops with no membrane covering.
3&4
Omphalocele – mass adjacent to the fetal anterior abdominal wall with a
membrane covering.
References or Suggested Reading:
1.
Creasy RK and Resnik R. Maternal-Fetal Medicine. Principles and Practice.
Philadelphia: Saunders; 1994.
2.
Fleisher AS, et al. Sonography in Obstetrics and Gynecology. Connecticut:
Appleton & Lange; 1996.
3.
Reece EA, Hobbins JC, Mahoney MJ, et al. Medicine of the Fetus and Mother.
Philadelphia: Lippincott; 1992.
4.
Callen PW. Ultrasonography in Obstetrics and Gynecology. Philadelphia:
Saunders; 1994.
5.
Harrison MR, Golbus MS, and Filly RA. The Unborn Patient, Prenatal Diagnosis
and Treatment. Philadelphia: Saunders; 1991.
6.
Romero R, Pilu G, Jeanty P, et al. Prenatal Diagnosis of Congenital Anomalies.
Connecticut: Appleton & Lange; 1988
7.
Twinning P, McHugo JM, and Pilling DW. Textbook of Fetal Abnormalities.
Edinburgh: Churchill Livingstone; 2000.
8.
Chervenak FA, Isaacson GC, and Campbell S. Ultrasound in Obstetrics and
Gynecology, Volume 2 USA: Hal; 1993.
9.
Jones KL. Recognizable Patterns of Human Malformation. Philadelphia: Saunders;
1997.
10.
Petrikovsky BM. Fetal Disorders, Diagnosis and Management. New York: WileyLiss; 1999.
11.
Fleischer AC, Romero R, Manning FA, et al. The Principles and Practice of
Ultrasonography in Obstetrics and Gynecology. Connecticut: Appleton & Lange;
1985.
About the Author
Junise Swanson received her Bachelors degree from the University of Kentucky in
Nursing in 1976. She also conducted further post-graduate studies in biology in 1987 from
the University of Louisville. She was a neonatal nurse for 14 years in the Neonatal Intensive
Care Unit at the University of Louisville Hospital. For the last 7 years she has been a
Perinatal Ultrasonographer at the Maternal Fetal Medicine Center at the University of
Louisville Hospital, Norton Healthcare’s Reproductive Testing Center, and The Maternal
Fetal Medicine Center of the Norton Suburban Hospital.
Jonathan Weeks, M.D. is a board certified Obstetrician / Gynecologist and
Perinatologist. He is currently director of the Maternal Fetal Medicine Center at Norton
Suburban Hospital. Dr. Weeks has several publications in peer-review medical journals and
has lectured at numerous meetings across the country.
Examination:
1.
Gastroschisis is a malformation of the abdominal wall that
A.
is commonly associated many different genetic disorders.
B.
usually occurs to the left of the umbilicus but the umbilicus is intact.
C.
only involves a few layers of the abdominal wall.
D.
has no membranous covering.
E.
allows abdominal contents to herniate through the base of the umbilicus.
2.
The incidence of gastroschisis worldwide is about
A.
1 per 10,000 live births.
B.
2 per 10,000 live births.
C.
3 per 10,000 live births.
D.
4 per 10,000 live births.
E.
5 per 10,000 live births.
3.
Omphalocele (Exomphalos) is a midline defect
A.
where the abdominal contents herniate to the right side of the umbilicus.
B.
that rarely contains the liver, bowel, and stomach.
C.
that allows abdominal contents to herniate through the base of the umbilicus.
D.
that has no membrane covering.
E.
where the abdominal contents herniate to the left side of the umbilicus.
4.
The incidence of omphalocele in live births worldwide is about
A.
7 per 10,000 and increases with maternal age.
B.
7 per 10,000 and decreases with maternal age.
C.
2 per 10,000 and increases with maternal age.
D.
2 per 10,000 and decreases with maternal age.
E.
4 per 10,000 and is not affected by maternal age.
5.
Gastroschisis is a defect resulting from a vascular compromise of
A.
the left umbilical vein
B.
the superior mesenteric artery
C.
the inferior mesenteric artery
D.
the splenic artery
E.
the omphalomesenteric artery
6.
During the development of the embryo, if the caudal fold tissue fails to fuse, it
results in
A.
cloacal extrophy of the bladder
B.
omphalocele
C.
gastroschisis
D.
Pentalogy of Cantrell
E.
ectopia cordis
7.
During the development of the embryo, if the lateral tissue folds fail to fuse, it results
in
A.
cloacal extrophy of the bladder
B.
omphalocele
C.
gastroschisis
D.
Pentalogy of Cantrell
E.
ectopia cordis
8.
The most common associated anomaly(s) seen with gastroschisis is (are)
A.
prune belly syndrome
B.
genitourinary tract abnormalities
C.
congenital heart defects
D.
intestinal tract complications
E.
hydrocephalus
9.
Associated anomalies seen with gastroschisis include all of the following except
A.
intestinal tract complications such as malrotation, atresia, and stenosis.
B.
ischemia of bowel sections due to kinking, and obstruction.
C.
congenital heart defects
D.
genitourinary tract abnormalities
E.
trisomy 18.
10.
In regard to omphalocele / exomphalos, chromosome abnormalities are seen in
about _______ of fetuses.
A.
10%.
B.
50%
C.
25%
D.
75%
E.
90%
11.
Omphalocele can be seen with numerous different chromosome abnormalities
including triploidy, which is a fetus with
A.
45 chromosomes missing an X
B.
C.
D.
E.
47 chromosomes with an extra X
47 chromosomes with an extra Y
47 chromosomes with an extra number 13
69 chromosomes
12.
Beckwith-Wiedemann syndrome may be associated with all of the following except
A.
an enlarged liver
B.
enlarged kidneys
C.
growth restriction
D.
omphalocele
E.
macroglossia
13.
The ultrasound findings for gastroschisis may include all of the following except
A.
multiple echogenic free floating bowel loops near the anterior abdominal wall
B.
no evidence of a membranous covering or sac
C.
polyhydramnios
D.
oligohydramnios
E.
an umbilical cord that inserts into the mass
14.
Factors that can sometimes make it difficult to identify gastroschisis include all of the
following except
A.
the size of the defect
B.
the fetal size
C.
the gestational age
D.
too much amniotic fluid (polyhydramnios)
E.
the fetal position
15.
It is important not to make an incorrect diagnosis of a fetal anomaly between the 8th
and 12th week of gestation because
A.
the fetal liver and spleen are not completely formed yet.
B.
the embryonic bowel normally protrudes into the base of the umbilical cord
during this time period and could mimic an anomaly.
C.
the amount of amniotic fluid is too low at this point in gestation to make an
accurate assessment.
D.
the fetal stomach bubble is not visible enough to confirm the presence of
bowel.
E.
the umbilical cord at this gestational age looks like bowel on ultrasound
imaging.
16.
The ultrasound findings for omphalocele include
A.
a solid appearing, round, echogenic mass adjacent to the anterior abdominal
wall
B.
an umbilical cord that inserts to the right of the mass
C.
an umbilical cord that inserts to the left of the mass
D.
no evidence of a membranous covering or sac
E.
a herniation of abdominal contents to the right of the umbilicus
17.
With a diagnosis of gastroschisis,
A.
B.
C.
D.
E.
the fetus should have follow-up ultrasounds to watch for macrosomia.
the fetus should have follow-up ultrasounds to watch for oligohydramnios.
karyotyping (genetic amniocentesis) should always be recommended because
most cases of gastroschisis are associated with chromosome abnormalities.
the patient should deliver by cesarean section
if the case is an isolated gastroschisis the overall prognosis is very poor with a
survival rate of less than 10%.
18.
Regarding a potential diagnosis of gastroschisis, one potential concern that may
result in some prenatal testing centers offering further genetic testing, such as
amniocentesis, is
A.
the issue that an omphalocele may have ruptured through its membrane
covering, mimicking the appearance of a gastroschisis.
B.
the presence of bowel ischemia due to kinking.
C.
the presence of oligohydramnios.
D.
the presence of an elevated maternal serum alpha-fetoprotein.
E.
the presence of bowel thickening due to prolonged exposure to amniotic
fluid.
19.
With a diagnosis of omphalocele / exomphalos,
A.
serial ultrasound evaluations are indicated to watch for macrosomia because
it is common with this disorder.
B.
rupture of the membrane covering is very common finding.
C.
karyotyping (genetic amniocentesis) is usually recommended, especially in the
presence of other anomalies.
D.
if the defect is large containing the liver, the patient should be informed that
it is less traumatic to the liver to deliver vaginally.
E.
the risk of stillbirth is rare because omphalocele is usually not associated with
other anomalies or chromosomal defects.
20.
Because of the other associated abnormalities, approximately ______ of fetuses
diagnosed with omphalocele will not survive.
A.
10%
B.
25%
C.
35%
D.
50%
E.
75%