A neonate presents with inability to pass meconium, abdominal distension, and bilious vomiting. Contrast enema shows a transition zone in the sigmoid colon with a dilated proximal colon. Which diagnosis does this confirm and what is the underlying pathology?

• A Meconium ileus — inspissated meconium in terminal ileum
• B Hirschsprung disease — absence of ganglion cells in submucosal and myenteric plexuses ✓
• C Anorectal malformation — incomplete canalization of the hindgut
• D Colonic atresia — intrauterine ischaemia of the colon

Explanation

The contrast enema transition zone (narrow aganglionic segment proximally transitioning to dilated normal ganglionated colon) in the sigmoid colon is the hallmark of Hirschsprung disease. The pathology is congenital absence of ganglion cells in the submucosal (Meissner) and myenteric (Auerbach) plexuses, resulting in a functional obstruction. Meconium ileus shows a microcolon with pellets of meconium in the terminal ileum. Anorectal malformations are diagnosed clinically and on cross-table lateral radiograph. Colonic atresia shows complete obstruction without a transition zone.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.