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BOWEL OBSTRUCTION PRENATAL IMAGING
Category: Child Health
Abstract : Prenatal imaging, especially with ultrasonography, can be extremely effective in
detecting of bowel obstruction. A fetus with proximal bowel obstruction may
present with polyhydramnios that occurs when the normally large volume of
amniotic fluid swallowed by the fetus remains in the amniotic sac. Approximately
50% of newborns with duodenal atresia have polyhydramnios. Polyhydramnios
incr
Prenatal imaging, especially with ultrasonography, can be extremely effective in
detecting of bowel obstruction. A fetus with proximal bowel obstruction may
present with polyhydramnios that occurs when the normally large volume of
amniotic fluid swallowed by the fetus remains in the amniotic sac. Approximately
50% of newborns with duodenal atresia have polyhydramnios. Polyhydramnios
increases the risk of premature birth.
The high resolution of fetal
ultrasonography and fetal magnetic resonance imaging (MRI) frequently enables
identification of abnormal features of the bowel in the fetus. Both studies
readily identify a dilated loop of bowel and are good predictors of a proximal
bowel obstruction such as atresia or volvulus.
In some situations, fetal
diagnosis of a proximal bowel atresia may prompt amniocentesis because a strong
relationship exists between some types of bowel obstruction and some chromosomal
anomalies. For example, children with duodenal atresia have a higher incidence
of trisomy 21. Thus, prenatal imaging of a bowel obstruction may complement
other modalities of prenatal counseling for parents.
Ultrasonography is
useful for identification of abnormal loops of bowel in the fetus. Unlike in the
newborn, the fetal bowel is gasless, without swallowed air that distorts the
image. As mentioned above, a dilated loop of small bowel may suggest an atresia
or volvulus. A whirlpool appearance to the bowel and bowel mesentery may
indicate malrotation with volvulus. Echogenic bowel suggests bowel compromise.
In approximately one third of fetuses with echogenic bowel on prenatal
ultrasonography, a malformation of the GI tract is later confirmed.
Some
prenatal ultrasonographic or MRI features are associated with specific
abnormalities in the fetus. A dilated proximal esophagus is often observed with
esophageal atresia. Bowel within the thoracic cavity confirms a congenital
diaphragmatic hernia. More subtle signs can be observed as well. Flecks of
calcification throughout the peritoneal cavity suggest meconium peritonitis from
prenatal bowel compromise and perforation and strongly suggest cystic fibrosis.
Finally, the nonspecific finding of ascites can suggest compromised bowel in the
fetus. Other nonsurgical causes of postnatal bowel dysfunction, such as
hydrocephalus or renal disease, may also be observed on prenatal imaging
studies.
The prenatal diagnosis of a bowel obstruction may directly
improve postnatal outcome by expediting its surgical management. Immediate
surgical intervention may be needed in patients with congenital diaphragmatic
hernia, esophageal atresia, or malrotation with volvulus. Many children with a
prenatal diagnosis of bowel obstruction are referred for delivery in a center
where pediatric surgeons are readily available.
In situations where
prenatal imaging has been used to diagnose an anatomic cause of bowel
obstruction, focused resuscitation in the delivery room may facilitate
preoperative stabilization. If positive pressure respiratory support is needed,
rapid intubation without prolonged bag-mask ventilation may minimize bowel
distention and improve outcome. A child born with a possible bowel obstruction
should undergo immediate nasogastric decompression because progressive bowel
distention from swallowed air may cause further compromise. Fluid sequestration
in a dilated loop of obstructed bowel may require aggressive parenteral fluid
administration to maintain the patient's hemodynamic stability. Preoperative
laboratory studies, antibiotics, and vitamin K may also be an appropriate part
of the delivery room resuscitation.
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