A 3-day-old boy is evaluated in the hospital nursery for the delayed passage of meconium. The patient is breastfed, has been feeding well every 2 hours, and is urinating over 8 times per day. He was born at 35 weeks gestation to a 27-year-old G4P4 mother. The patient is of Ashkenazi Jewish descent and the patient’s parents refused all prenatal genetic testing. The pregnancy was uncomplicated until the patient’s mother had a spontaneous rupture of membranes at 35 weeks of gestation. The patient’s 3 older siblings are all healthy. The patient’s temperature is 98.2°F (36.8°C), blood pressure is 48/32 mmHg, pulse is 164/min, and respirations are 48/min. On physical exam, he appears to be in moderate distress. He has no dysmorphic features, and his abdomen is distended and non-tender. Bowel sounds are absent. Which of the following is the most appropriate next step in management?
Upper gastrointestinal series
Sweat testing
Abdominal radiograph
Abdominal CT
Abdominal radiograph
Delayed passage of meconium should be evaluated with an abdominal radiograph to rule out bowel perforation. Patients with a perforation require emergency surgery.

All neonates should pass meconium in the first 48 hours of life. Patients that fail do to so should be evaluated with an abdominal radiograph to exclude the possibility of bowel perforation. If free air is seen on the abdominal radiograph, patients should be taken for emergent surgery to repair the perforation. If bowel perforation is ruled out, a workup should be done to determine the etiology of the delayed passage, which would most likely include a contrast enema to differentiate between meconium ileus and Hirschsprung disease. Treatment is with meconium removal or excision of the defective segment respectively.

Adams and Stanton review the evidence regarding the diagnosis and treatment of neonatal bowel obstruction. They discuss how malrotation, jejunoileal atresia, duodenal atresia, and colonic atresia are common causes of this finding. They recommend surgical management of these conditions.

Incorrect Answers:
Answer A: An abdominal radiograph would be faster than an abdominal CT to rule out an indication for emergency surgery. The use of CT should also be restricted in the pediatric population due to the radiation exposure involved. Adult patients with unclear radiographic findings can be further assessed using a contrast CT scan.

Answer C: Contrast enema is the test of choice to differentiate meconium ileus from Hirschsprung disease, but the most important first step is to rule out bowel perforation. Patients who do not have perforation can then undergo this test to determine the etiology of failure to pass meconium.

Answer D: Sweat testing would aid in the diagnosis of cystic fibrosis, particularly in this patient who has had no prenatal screening. The first step in management should be an abdominal radiograph to rule out bowel perforation. Cystic fibrosis can be treated with pancreatic enzyme replacement and pulmonary therapy.

Answer E: Upper gastrointestinal series is used to make the diagnosis of intestinal malrotation, which more commonly presents with bilious vomiting secondary to midgut volvulus rather than the delayed passage of meconium. Treatment is with surgical derotation.

Bullet Summary:
Neonates who fail to pass meconium in the first 48 hours of life should be urgently evaluated with an abdominal radiograph to rule out bowel perforation.