Diagnostic ultrasound ( PDFDrive )

1312 PART IV Obstetric and Fetal Sonography
complicated by vesicocolic istula, intraluminal calciications
may be seen and have been attributed to mixing of meconium
with urine. 84 More recently, inability to visualize the anal mucosa
on transverse transperineal view (known as the anal dimple,
which is the result of the echogenic mucosa surrounded by the
hypoechoic muscle of the anal sphincter) has been suggested as
an important sonographic marker in cases of imperforated anus
(Fig. 38.10B). 85
Hirschsprung Disease
Hirschsprung disease is a congenital disorder of the colon caused
by absence of ganglia in the distal colon, thereby leading to
functional colonic obstruction. It afects about 1 of 5000 live
births. 86 he diseased segment usually involves the most distal
part of the colon, including the internal anal sphincter, and
extends proximally to involve variable portions of the colon,
with the most severe forms involving the whole colon.
Hirschsprung disease is associated with chromosomal and
structural abnormalities in about 10% to 20% of cases, and up
to 10% of cases are associated with trisomy 21. 87
Prenatal diagnosis of Hirschsprung disease is uncommon and
is usually made in severe forms involving the entire length of
colon. he sonographic signs in these cases are nonspeciic and
include bowel dilatation, polyhydramnios, and echogenic bowel
(Fig. 38.11). 87 hus the majority of cases are diagnosed within
the early neonatal period, with the most common sign being
failure to pass meconium. 88-90
Enteric Duplication Cysts
Enteric duplication cysts are classiied by the anatomic region
involved rather than by the histology of the mucosal lining. 91
he incidence is estimated at 1 per 10,000 infants. 92,93 hey result
from abnormal recanalization of the GI tract and may or may
not communicate with the lumen of the GI tract. Enteric duplication
cysts can be associated with any area of the GI tract, but
they are most common in the terminal ileum. 94 hey may present
A
B
C
FIG. 38.11 Hirschsprung
Disease. (A) Coronal image at 36
weeks shows distended bowel
loops with echogenic walls
(arrows). (B) Transverse view in
the same fetus shows normal labia
(arrowheads) and anal dimple
(arrow). This was the third affected
child for this couple. The father also
had the disease. (C) In another
fetus, note multiple dilated loops
of bowel throughout the abdomen.