Diagnostic ultrasound ( PDFDrive )

CHAPTER 38 The Fetal Gastrointestinal Tract and Abdominal Wall 1309
S
A
B
FIG. 38.6 Heterotaxy With Asplenia or Polysplenia. (A) Polysplenia. Transverse MRI of fetus with complex congenital heart disease (not
shown) with multiple splenules (arrows) in the left upper quadrant. S, Stomach. (B) Asplenia in a transverse image from an autopsy MRI in a term
infant with nonreparable, complex congenital heart disease as part of a heterotaxy syndrome shows asplenia with central liver placement. The
portal vein (arrowheads) bifurcates centrally. The arrow denotes the umbilical vein. LK, Left kidney; RK, right kidney.
FIG. 38.7 Gastric Debris. Transverse image through the abdomen
in a 25-week fetus shows a masslike structure in the stomach (arrowhead).
This is a benign inding thought to represent swallowed debris or vernix.
Sp, Spine. See also Videos 38.2 and 38.3.
he sonographic hallmarks in cases of duodenal atresia
are the presence of severe polyhydramnios (which may
not be present until the late second or third trimester) and the
“double-bubble” sign, in which a second echolucent mass is
seen medial to the stomach bubble in a transverse view of
fetal abdomen (Fig. 38.8, Video 38.4). his sign is the result of
the dilated segment of the duodenum proximal to the atretic
area and is highly suggestive of duodenal obstruction. It is
important to demonstrate continuity between the luidilled
structures to prove that the diagnosis is duodenal
stenosis/atresia.
A prominent incisura angularis of the stomach may be
mistaken for a “double bubble” if these are in diferent planes,
but a careful real-time longitudinal examination of the stomach
can eliminate this possibility. Other, less common reasons for
an apparent double-bubble sign include choledochal cyst and
duodenal duplication cyst. 43,47 In addition, several cases of
transient double-bubble sign during the second trimester have
been reported, with normal outcomes. 48,49
As in all cases of proximal bowel obstruction, polyhydramnios
is frequently present by the late second trimester 50-52 but is oten
absent in the early second trimester at the time of routine fetal
survey. his is in part related to the relative diference in the
amount of amniotic luid swallowed per day at diferent times
of gestation. he fetus swallows a relatively small amount of
amniotic luid (2-7 mL of luid per day) during early second
trimester, compared to 450 mL at term. 53 In a European study
of 138 cases of postnatally conirmed duodenal atresia, polyhydramnios
was present in only 33% of cases. 54 For these reasons,
duodenal atresia is commonly diagnosed during the third trimester,
whereas in the early second trimester both false-negative
and false-positive diagnoses have been reported. 48,49 hus the
proportion of cases diagnosed prenatally ranges widely between
34% and 87%. 43,50,55-57
It has been suggested that prenatal diagnosis of duodenal
atresia has the potential to decrease neonatal morbidity. 50 Finding
the double-bubble sign should trigger detailed anatomic survey,
fetal echocardiography, as well as genetic counseling and consideration
of amniocentesis given the high association with
trisomy 21.