Dilated loops of Fetal Bowel
· Pyloric atresia- Sonographic features include PH and dilatation of the stomach. The small bowel may be normally visualized because of the passage of bile.
· Non-specific gastric dilatation- Transient non-specific dilatation of
the stomach may present in normal fetuses. Repeat examination
differentiates from pyloric atresia.
· Normal- As gestation advances, the small bowel increases in size and the
lumen becomes apparent. Fetal small bowel rarely exceeds 6 mm
in diameter at term.
· Cystic fibrosis- Thirty-three percent of fetuses presenting with dilated bowel distal to the duodenum have cystic fibrosis. Newborns presenting with large bowel obstruction have a 36% incidence of cystic fibrosis.
· Meconium peritonitis- This is chemical peritonitis due to the presence of meconium released by a bowel perforation which may result in the formation of a pseudocyst or generalized ascites; fine particles within the ascites have been described as giving a ‘snowstorm’ appearance. Meconium deposits may calcify.
· Smalll bowel atresia- Any segment of bowel may become atretic. The more distal the atresia, the lower the incidence of PH. Third trimester PH is only present in 20—30% of jejunal atresia.
· Secondary to large bowel obstruction- Large bowel obstruction may occur as a result of anorectal atresia. Meconium plug syndrome, Hirschsprung’s disease or megacystis—microcolon—intestinal hypoperistaltis syndrome (MMIHS).
· Gastroschisis- Mild dilatation of the bowel is common with gastroschisis, and does not necessarily indicate obstruction, but marked dilatation may be secondary to bowel obstruction as a result of ischemia associated with volvulus. Bowel wall thickening is usually seen.
· Midgut volvulus-Delayed return of the fetal midgut from the umbilical cord and failure of fixation results in malrotation. This may result in volvulus, bowel obstruction and ischemia of the small bowel.
· Congenital choridorrhea-A rare hereditary disorder characterized by impairment of active chloride transport from the distal ileum and colon. This results in dilated loops of bowel in utero. Associated PH has been reported.
· Hirschsprung's disease- The incidence of Hirschsprung’s disease is 1:10000. Dilated ioops of bowel, PH and increase in abdominal circumference have been reported, although uncommon.
· Meconium plug syndrome-Associated with cystic fibrosis.
· Normal- Occasionally meconium in the fetus may appear echo poor, mimicking dilated loops of bowel. The large bowel is easily visualized after 28 weeks. Large bowel lumen is seldom more than 1 cm in diameter at term.
· Anorectal atresia- Imperforate anus occurs in approximately 1 in 5000 live- births. More complex anorectal atresias are less common, and are frequently associated with fistulas into the urethra or perineum in males. Large bowel dilatation is occasionally evident on US. There may be features of associated sacral agenesis, lower limb hypoplasia or VACTERAL syndrome.
Megacystis microcolon (MMIHS)-Associated with functional small bowel obstruction, malrotation, microcolon and enlarged, non- obstructed urinary bladder. There may be associated hydronephrosis.
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