Diagnostic ultrasound ( PDFDrive )

CHAPTER 38 The Fetal Gastrointestinal Tract and Abdominal Wall 1311
1
A
B
FIG. 38.9 Jejunal and Ileal Atresia. (A) Jejunal atresia. Coronal image through the abdomen of a 30-week fetus shows several dilated loops
of small bowel (arrows). (B) Ileal atresia. Transverse fetal abdomen with multiple dilated loops of bowel. The bowel lumen is measured in the
largest transverse diameter (calipers). See also Video 38.5.
A
B
FIG. 38.10 Normal Colon and Anal Dimple. (A) Normal third-trimester large bowel. Transverse image through the abdomen at 37 weeks
shows prominent meconium-illed loops of colon. This is normal in the third trimester and should not be taken to indicate bowel obstruction. RK,
Right kidney; Sp, spine. (B) Although not part of standard scan guidelines, the anal dimple (arrow) can easily be demonstrated on a transverse plan
through the perineum. Visualization of the dimple excludes anal atresia.
malformations ranges from isolated imperforate anus to more
complex cloacal malformations. hey are classiied as low,
intermediate, and high based on whether the bowel ends below,
at the same level, or above the level of the levator ani muscle,
respectively. he majority of cases (>90%) are low malformations.
74 High malformations are less common and are oten
associated with vesicocolic istulas.
Anorectal malformations are frequently associated with
chromosomal and structural anomalies, in 48% to 98% of cases. 75-77
Anal atresia is also part of the VACTERL sequence 76-78 and is
associated with a large number of genetic syndromes. Given the
high rate of associated abnormalities, a detailed fetal survey,
fetal echocardiogram, genetic counseling, and discussion of
aneuploidy risk should be included in the management of cases
with suspected anorectal malformations.
he prenatal detection rate of anorectal malformations is lower
than that of more proximal types of bowel obstruction and ranges
from 7% to 24%. 55,79,80 he main sonographic sign is dilated
loops of small or large bowel, although this should be distinguished
from normal prominent colon loops during the third
trimester (Fig. 38.10A). Polyhydramnios is absent in the majority
of cases. 81,82 Sonographic assessment would commonly reveal
signs of associated anomalies such as in the case of VACTERL
association and associated chromosomal abnormalities. 83 In cases