The newborn nursery calls to notify you that a 1-day-old baby boy has developed abdominal distension and bilious emesis. Prenatal history was significant for areas of echogenic bowel seen on ultrasound. You order an abdominal radiograph; based on the results you order a contrast enema. Both are shown here. This infant is most likely to have which of the following?

(b) Source: (Kliegman et al, pp 600-601. McMillan et al, p 1428. Rudolph et al, p 1427.) The radiographs are consistent with meconium ileus, a condition virtually pathognomonic for CF. Approximately 15% of children with CF will present with meconium ileus. Echogenic bowel on prenatal ultrasound can be an early hint. Inspissated meconium obstructs the small bowel, usually at the level of the terminal ileum. Radiographs show dilated loops of bowel, and usually reveal a bubbly or granular pattern at the level of obstruction. The enema shows microcolon from disuse. Complications of meconium ileus may include perforation and meconium peritonitis. Meconium ileus should be distinguished from meconium plug, which is a functional obstruction of the colon that can be associated with Hirschsprung disease but not usually with CF. With meconium plug, a water-soluble high osmolality contrast enema may be diagnostic as well as therapeutic.