A 3-day-old boy is evaluated in the neonatal intensive care unit for failure to pass meconium. The patient is otherwise doing well and feeding every 2 hours. He is urinating 8-10 times per day. The patient has had 2 episodes of vomiting that were described as green in color. He was born at 39 weeks gestation to a 38-year-old G3P3 mother. The pregnancy was uncomplicated, and the patient’s mother received routine prenatal care. She declined prenatal testing. One of the patient’s older siblings has Down syndrome. 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, the patient is in no acute distress. His abdomen is firm, non-tender, and distended with hypoactive bowel sounds. A digital rectal exam fails to relieve the obstruction. An abdominal radiograph is performed and the result can be seen in Figure A. Which of the following is the most appropriate next step in management?
Sweat testing
Contrast enema
Upper gastrointestinal series
Abdominal CT
Contrast enema
This patient presents with delayed passage of meconium, bilious emesis, unsuccessful disimpaction on digital rectal exam, and dilated loops of bowel on abdominal radiograph which suggests a diagnosis of meconium ileus. The most appropriate next step in management is an enema with water-soluble contrast which may be both diagnostic and therapeutic.

Meconium ileus presents with bilious emesis and failure to pass meconium in the first 48 hours of life. Abdominal radiography typically shows dilated loops of the small intestine proximal to the obstruction. Enema with water-soluble contrast (Gastrografin) is both diagnostic and therapeutic, as the contrast not only visualizes a microcolon but also relieves the obstruction via the osmotic pull of water into the lumen of the colon. Surgery may be necessary if the contrast enema fails. Patients should also be evaluated for underlying conditions such as cystic fibrosis.

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.

Figure/Illustration A is an abdominal radiograph demonstrating dilated loops of bowel and a “soap bubble” appearance of meconium mixed with bowel gas in the right lower quadrant (red circle). These findings are classically seen in patients with meconium ileus.

Incorrect Answers:
Answer A: An abdominal radiograph would be faster but less accurate than an abdominal CT. The use of CT should also be restricted in the pediatric population due to the radiation exposure involved.

Answer C: Rectal suction biopsy is the most accurate test to diagnose Hirschsprung disease, which may present like meconium ileus with bilious vomiting, delayed passage of meconium, and dilated loops of bowel on an abdominal radiograph. A digital rectal exam typically temporarily relieves the intestinal obstruction in Hirschsprung disease and produces an expulsion of gas and stool called the “squirt sign.”

Answer D: Sweat testing is used to diagnose cystic fibrosis, which is strongly associated with meconium ileus. An enema with water-soluble contrast would be the best next step to both confirm the diagnosis and relieve the obstruction. The patient should subsequently undergo sweat testing.

Answer E: Upper gastrointestinal series is the diagnostic test of choice for intestinal malrotation which may also present with bilious vomiting. Malrotation is less likely to present with delayed passage of meconium, and an abdominal radiograph would more likely demonstrate a midgut volvulus. Treatment is with surgical derotation.

Bullet Summary:
Patients with meconium ileus should undergo an enema with water-soluble contrast (Gastrografin) to both confirm the diagnosis and relieve the obstruction.