Diagnostic ultrasound ( PDFDrive )

CHAPTER 38 The Fetal Gastrointestinal Tract and Abdominal Wall 1305
dorsal part of the yolk sac into the embryo following the longitudinal
and lateral folding of the embryonic disc. he gut tube
is lined by the embryonic endoderm and is closed at its cranial
and caudal ends by the oropharyngeal membrane and the cloacal
membrane, respectively. 1 Subsequently, the gut tube undergoes
regionalization into three portions. he foregut, the most cranial
portion, gives rise to the esophagus, stomach, duodenum, liver
and bile ducts, and pancreas. he hindgut, the most caudal
portion, diferentiates into the distal part of the colon (beyond
the splenic lexure), which is partially supplied by the inferior
mesenteric artery. In between, the midgut gives rise to the largest
part of the intestine, which is supplied by the superior mesenteric
artery, and includes the second half of the duodenum (distal to
the ampulla of Vater), jejunum, ileum, ascending colon, and the
proximal two-thirds of the transverse colon. he midgut remains
in connection with the yolk sac via the yolk stalk (omphalomesenteric
duct or vitelline duct). 2-6
Esophagus
Esophageal Atresia
he normal fetal esophagus, extending from the pharynx to the
stomach, is collapsed and may therefore be diicult to visualize,
or it may be demonstrated as two or four echogenic lines representing
the esophageal walls.
Developmentally, the trachea and esophagus diferentiate
inferiorly from the posterior pharynx. Incomplete diferentiation
of the respiratory and GI tracts can lead to esophageal atresia
with or without tracheoesophageal istulas. he incidence of
all types of tracheoesophageal istulas is 2.8 per 10,000 pregnancies.
7,8 here are ive types of esophageal atresia, 9 with the
most common having a istula to the distal esophagus. Because
most types of esophageal atresia (90%) 10 are associated with
tracheoesophageal istulas, in many cases the stomach (although
oten small) will be visualized on ultrasound, and polyhydramnios
may be absent or mild or present only later in gestation
(Table 38.1).
he main sonographic signs of esophageal atresia include
absent or small stomach (Fig. 38.1), polyhydramnios, and the
esophageal pouch sign (luid collection in the blind end of the
esophagus) 11 (Fig. 38.2A). At times a distended oropharynx will
be seen (Fig. 38.2B, Video 38.1). However, the demonstration
of esophageal pouch can be diicult because of variation in the
location and periodic emptying of the pouch. he antenatal
diagnosis of esophageal atresia is challenging, and in many cases
the diagnosis is only made during the neonatal period. One
TABLE 38.1 Types of Esophageal Atresia
Type Description Proportion of Esophageal
Atresia (EA) Cases
A EA without tracheoesophageal (TE) istula 10%
B EA with TE istula to the proximal esophageal segment <1%
C EA with TE istula to the distal esophageal segment 85%
D EA with TE istula to both proximal and distal esophageal segments <1%
E TE istula without esophageal atresia 5%
A
B
FIG. 38.1 Esophageal Atresia and Absent Stomach. (A) Transverse ultrasound through the abdomen in a 25-week fetus shows no visible
stomach. Polyhydramnios is present; vertical pocket of amniotic luid (X marks) measured >8 cm. Sp, Spine. (B) Third-trimester fetus with absent
stomach and polyhydramnios.