Diagnostic ultrasound ( PDFDrive )

1310 PART IV Obstetric and Fetal Sonography
A
B
FIG. 38.8 Duodenal Atresia. (A) Oblique sagittal view through the fetal abdomen at 33 weeks shows the “double-bubble” sign of duodenal
atresia with the luid-illed stomach (St) and duodenum (D). Ht, Heart. (B) Oblique coronal view shows continuity (arrow) between the stomach
and duodenum. See also Video 38.4.
Jejunal and Ileal Obstruction. he prevalence of jejunoileal
atresia ranges from 0.5 to 1.1 cases per 10,000 live births. 58,59
Jejunal atresias are slightly more common (51%) than ileal. 60
he most common hypothesis with respect to the etiology for
jejunoileal atresia is early vascular compromise of the developing
midgut. 57 In animals, induced vascular compromise leads to
isolated bowel atresias. 61 his hypothesis is also supported by
the association of intestinal atresia with placental complications
and other abnormalities of vascular origin such as gastroschisis. 62
“Apple peel” jejunal atresia is a subtype that involves agenesis
of the mesentery, is more oten familial, 54,63,64 and is likely of a
diferent etiology. Cystic ibrosis is a common underlying cause
of ileal obstruction; the thick meconium associated with cystic
ibrosis can lead to ileal obstruction (meconium ileus) with or
without echogenic bowel. 65,66
Although jejunal and ileal atresia are oten discussed as a
single entity, there are major diferences between these two
conditions. Jejunal atresia is more likely to involve multiple sites
and is less oten associated with in utero perforation than is ileal
atresia, likely because of the lower compliance of the ileum. In
addition, the risk of associated anomalies depends on the site
of obstruction. Whereas jejunal atresias have been associated
with extra-GI anomalies and chromosomal disorders in up to
42% of cases, the rate of associated anomalies in cases of ileal
atresia is only about 2%. 54,67 Both conditions are associated with
other GI abnormalities, including malrotation, meconium
peritonitis, and duplication cysts. 68
he prenatal diagnosis of jejunoileal obstruction is based on
dilated loops of bowel (Fig. 38.9, Video 38.5), most frequently
without a dilated stomach and sometimes with hyperperistalsis.
If peristalsis is not observed, dilated small bowel can be diicult
to distinguish from dilated colon. he cutof used to deine dilated
small bowel is greater than 7 mm for loop diameter or greater
than 13 mm for loop length. 65 he diagnosis of jejunoileal atresia
is typically not made until late in the second trimester, as dilatation
of the bowel is oten not seen before that stage. he rate of
polyhydramnios decreases as the site of bowel obstruction
becomes more distal. hus polyhydramnios in cases of jejunoileal
atresia is less common than in cases of duodenal or esophageal
atresia; it has been reported in about one-third of cases of jejunal
atresia and is even less common in cases of ileal atresia. 69 It is
oten not possible to conidently diferentiate between jejunal
and ileal atresia in utero; the more dilated loops visible, the more
likely it is to be a distal or ileal obstruction. Another sonographic
sign associated with jejunoileal obstruction is echogenic bowel,
relecting thickened meconium due to the intestinal stasis. Ascites
and abdominal calciications can be seen in cases of obstruction
complicated by perforation, a complication seen more commonly
in cases of ileal obstruction. In a recent systematic review on
the accuracy of sonographic diagnosis of small bowel obstruction,
a large variation in the detection rate of small bowel obstruction
was noted (10%-100%), with the detection rate being considerably
higher for jejunal atresia (66%) than for ileal atresia (26%). 70
Meconium Ileus
Meconium ileus relates to obstruction of the ileum by thickened
meconium. Some cases are associated with cystic ibrosis, but
only a minority (up to 20%) of cases of cystic ibrosis will present
with meconium ileus during pregnancy. 71,72 he presence of
echogenic bowel in addition to the general sonographic signs
of bowel obstruction increases the likelihood of meconium ileus.
he diferential diagnosis and diagnostic approach in cases of
echogenic bowel and meconium peritonitis are discussed later
in this chapter.
Anorectal Malformations
he incidence of anorectal malformation is in the range of 0.8
to 4 per 10,000 live births. 73 he spectrum of anorectal