Best Next Step in Diagnosis
The best next step is a contrast enema (barium enema), which is the diagnostic imaging procedure of choice for suspected distal bowel obstruction in this clinical scenario. 1
Clinical Reasoning
This 2-day-old neonate presents with the classic triad highly suggestive of Hirschsprung disease:
The pathognomonic finding of a gush of stool on rectal examination strongly suggests Hirschsprung disease, as this indicates functional obstruction with retained stool proximal to the aganglionic segment. 2
Diagnostic Algorithm
Step 1: Contrast Enema First
Contrast enema is the diagnostic imaging procedure of choice when there is suspected distal obstruction, as it can differentiate between:
- Temporary functional abnormalities requiring only observation (meconium plug) 1
- Pathologies requiring surgery (ileal atresia) 1
- Conditions requiring therapeutic enema (meconium ileus) 1
- Hirschsprung disease requiring rectal biopsy 1
The contrast enema will demonstrate:
- A transition zone between the narrow aganglionic segment and dilated proximal colon in Hirschsprung disease 2
- Microcolon in cases of structural atresia 1
- Meconium plugs that may be therapeutically evacuated 5
Step 2: Rectal Biopsy Only After Positive Contrast Enema
Rectal biopsy should be performed only after the contrast enema demonstrates findings suggestive of Hirschsprung disease (transition zone). 2 Research demonstrates that 100% of Hirschsprung patients had one or more key features including delayed meconium passage, abdominal distension, vomiting, or transition zone on contrast enema. 2
Why Not the Other Options?
US Abdomen - Not Indicated
There is no relevant literature supporting the use of ultrasound in evaluating neonates with suspected distal obstruction. 1, 6 The ACR Appropriateness Criteria explicitly state ultrasound has no role in this clinical scenario. 1
Rectal Biopsy - Premature Without Imaging
While rectal biopsy is the definitive diagnostic test for Hirschsprung disease, performing it without prior contrast enema would miss other treatable causes of distal obstruction (meconium plug, meconium ileus, ileal atresia) that present identically on clinical examination. 1 The contrast enema guides whether biopsy is necessary and can be therapeutic in some conditions. 5
Critical Pitfall to Avoid
Do not assume this is Hirschsprung disease and proceed directly to rectal biopsy. The clinical presentation is identical for multiple causes of distal obstruction, and contrast enema is both diagnostic and potentially therapeutic. 1 In 36% of patients with similar presentations, Hirschsprung disease can be excluded by imaging findings alone. 2