Update September 23, 2018



A 3-day-old infant develops bilious vomiting, abdominal distention, and intestinal obstruction. Plain films of the abdomen reveal dilated air filled loops of small intestine without air fluid levels and the appearance of “soap bubbles” in the bowel. The colon is small on contrast enema, and there is obstruction of the terminal ileum. Which of the following is the most likely underlying cause of this disorder?

The correct answer is A.

The patient has a meconium ileus. The “soap bubble” pattern is caused by air trapped within the thickened meconium and is highly suggestive, but not pathognomonic, of meconium ileus. Pyloric stenosis (C) is associated with bilious vomiting, but gaseous dilation of the small bowel would not be expected, and most cases of pyloric stenosis occur after 3 weeks of life. Hirschsprung disease (B) can cause delayed passage of meconium and may be associated with a small colon initially, but most cases of meconium ileus are associated with cystic fibrosis.