Diagnostic ultrasound ( PDFDrive )

CHAPTER 38 The Fetal Gastrointestinal Tract and Abdominal Wall 1325
to 60% of cases) and stillbirth (4.5%-12%) have been reported
in fetuses with gastroschisis. In a recent meta-analysis, the
incidence of stillbirth ater 36 weeks was only 1.3%. 209 he
mechanism responsible for the increased risk of fetal growth
restriction and stillbirth remains unclear. 190,206,210
Management
Initial management of gastroschisis involves detailed sonographic
assessment to conirm the diagnosis and assess the extent of the
abdominal wall defect and involved organs. he presence of
associated anomalies on ultrasound should be documented. Close
monitoring with ultrasound and nonstress test are indicated
during the third trimester given the increased risk of fetal growth
restriction, fetal demise, and GI complications (e.g., obstruction
and perforation), although clear guidelines regarding the onset
and frequency of monitoring are lacking. he presence of dilated
stomach and/or dilated loops of bowel, either within the fetal
abdomen or within the amniotic cavity, should be documented.
Fetal weight estimation should be done using formulas that are
based on indices of fetal head and femur length but not abdominal
circumference to avoid underestimation of fetal weight. 211
he optimal timing of delivery is debated. Given the increased
risk of stillbirth and the concern that prolonged in utero exposure
of the bowel to amniotic luid may worsen outcomes, two
trials compared the outcome of fetuses that were born preterm
(average, 35 weeks) versus those delivered at term or for abnormal
fetal testing. 212,213 Neither trial showed an improved outcome
in the preterm group. hus delivery prior to 37 weeks should
be considered only in cases of fetal growth restriction or abnormal
fetal testing. here is no evidence supporting early delivery
in cases of bowel dilatation. In a recent study of 296 pregnancies
complicated by gastroschisis, it was found that induction of
labor at 37 weeks of gestation was associated with reduced risks
of sepsis, bowel damage, and neonatal death compared with
pregnancies managed expectantly beyond 37 weeks of gestation.
214 hese data may support a practice of routine delivery in
the early term period (37-38 weeks). With respect to mode of
delivery, there is no evidence that cesarean delivery improves
neonatal outcome, and therefore cesarean delivery should be
reserved for the usual obstetric indications. 215 Neonatal outcome
in cases of gastroschisis is associated with an overall survival
rate of over 90%, although outcome is less favorable in cases of
complex gastroschisis. 216,217
Omphalocele
Omphalocele refers to herniation of the intestine and
other abdominal organs into the base of the umbilical cord
through an enlarged umbilical ring, with the umbilical
cord inserting at the apex of the herniated sac. he herniated
content is covered by amnion and peritoneum (Fig. 38.30,
Video 38.13).
Epidemiology
he incidence of omphalocele varies geographically, from 0.6
per 10,000 births in Japan 191 to 6 per 10,000 births in the British
Isles. 202,206 In a registry-based study from the United States, the
incidence of omphalocele was 1.92 per 10,000 live births. 218
Omphalocele has been reported to be more common in women
35 to 40 years old 191 and also among women younger than 20
years. 218 Other associations include male sex and multiple
gestations. 218
Prenatal Diagnosis
In the irst trimester, physiologic midgut herniation can
be mistaken for an omphalocele. his normal inding is
limited to herniation of bowel loops and should resolve by 12
weeks. It should never include the liver, and the herniation
should not be more than 1 cm into the cord. he presence
of even small herniation into the base of the umbilical cord
beyond 12 weeks is therefore diagnostic of omphalocele
(Fig. 38.30B).
Most cases of omphalocele are readily detected at the time
of the second-trimester scan as a protrusion of abdominal content,
mainly small bowel loops, into the base of the umbilical cord,
contained within a sac consisting of peritoneum and amniotic
membrane. In cases of large defects, the omphalocele may contain
other organs such as liver and stomach (Fig. 38.31). he umbilical
cord can be seen inserted on the herniated sac rather than directly
to the abdominal wall.
Associated Conditions
In contrast to gastroschisis, omphalocele is commonly associated
with chromosomal abnormalities (10%-30%) 191,202 and additional
structural abnormalities (55%-58%). 202,208,219 he most common
aneuploidies are trisomies 13 and 18. 220,221 he risk of genetic
abnormalities is higher in the presence of additional structural
abnormalities as well as in cases with a small defect when the
herniated content is limited to small bowel (see Fig. 38.30B).
hus cases where the liver is found in the omphalocele are less
likely to be associated with chromosomal abnormalities. Omphalocele
is associated with several single gene mutation syndromes
(including autosomal dominant, autosomal recessive, and X-linked
recessive disorders), 222 and Beckwith-Weidemann syndrome.
Beckwith-Weidemann syndrome involves a mutation or deletion
of imprinted genes within the chromosome 11p15.5 region and
is associated with omphalocele, macroglossia, and overgrowth
(Fig. 38.32).
Associated structural abnormalities are common and include
midline defects (cardiac, clet lip and palate, and spinal/vertebral
anomalies), clubfoot, and central nervous system anomalies. 219
Because of the common association with aneuploidies and
multisystem anomalies, many of these pregnancies are terminated,
potentially biasing outcome data.
Management
he inding of fetal omphalocele should trigger a detailed evaluation
for the presence of associated structural anomalies, including
fetal echocardiography. 223 Genetic counseling is recommended
and amniocentesis should be ofered to assess for karyotype or
microarray, as well as for screening for speciic genetic syndromes,
including Beckwith-Wiedemann syndrome.
Fetal monitoring with serial ultrasound examinations is
recommended given an increased risk for polyhydramnios, ascites,
fetal growth restriction, and stillbirth. As in the case of