What is the initial step in managing an infant with delayed passage of meconium and a gush of stool on rectal exam?

Initial Diagnostic Step: Contrast Enema

In an infant with delayed passage of meconium who has a gush of stool on rectal examination, the initial step is to obtain a contrast enema, as this finding is highly suggestive of Hirschsprung disease. 1

Clinical Significance of the "Gush Sign"

• The gush of stool on rectal examination is a classic finding in Hirschsprung disease, occurring when the examining finger relieves the functional obstruction caused by the aganglionic segment 1
• This finding helps distinguish Hirschsprung disease from other causes of delayed meconium passage, such as meconium plug syndrome, meconium ileus, or intestinal atresia 1

Diagnostic Algorithm

Step 1: Plain Abdominal Radiograph

• While the contrast enema is the definitive diagnostic test, an initial plain abdominal radiograph should be obtained to assess the bowel gas pattern and rule out perforation 1
• Radiographs may show dilated proximal bowel loops with absent or decreased distal gas, consistent with distal bowel obstruction 1

Step 2: Contrast Enema (Definitive Diagnostic Test)

• Fluoroscopy contrast enema is the appropriate next imaging study for an infant with radiographic findings suggesting distal bowel obstruction 1
• The contrast enema in Hirschsprung disease typically demonstrates:
  • A transition zone between the dilated proximal bowel and the narrowed aganglionic distal segment 1
  • Delayed evacuation of contrast on 24-hour follow-up films 1
  • A rectosigmoid ratio less than 1 (the rectum is narrower than the sigmoid colon) 1

Step 3: Rectal Suction Biopsy

• Following a positive contrast enema, rectal suction biopsy is required to confirm the absence of ganglion cells and establish the definitive diagnosis of Hirschsprung disease 1

Important Clinical Pitfalls

• Do not delay diagnostic imaging while waiting for spontaneous passage of meconium, as this can lead to enterocolitis, the most serious complication of Hirschsprung disease 1
• Long-segment Hirschsprung disease (extending proximal to the ileocecal valve) may present with milder symptoms and delayed diagnosis, making clinical suspicion critical 2
• In premature infants, delayed meconium passage may be due to meconium plug syndrome related to maternal magnesium sulfate therapy, but the gush sign is more specific for Hirschsprung disease 3

Differential Considerations

While the gush sign strongly suggests Hirschsprung disease, other causes of delayed meconium passage to consider include:

• Meconium plug syndrome: More common in premature infants exposed to maternal magnesium sulfate; contrast enema is both diagnostic and therapeutic 3
• Meconium ileus: Associated with cystic fibrosis; presents with abdominal distension and may require Gastrografin enema 4
• Intestinal atresia: Presents with complete obstruction; contrast enema shows microcolon 5
• Malrotation: Requires upper GI series for diagnosis, not contrast enema 1

Management Priorities

• Maintain NPO status and provide intravenous fluid resuscitation 6
• Place nasogastric tube for gastric decompression 6
• Obtain urgent pediatric surgical consultation once Hirschsprung disease is confirmed 1
• Monitor for signs of enterocolitis (fever, bloody diarrhea, sepsis), which requires emergent decompression 1