A newborn born at 39 weeks' gestation fails to pass meconium within the first 48 hours of life. The infant develops progressive abdominal distension and bilious vomiting. Digital rectal examination reveals a tight anal sphincter, and upon withdrawal of the finger, there is an explosive expulsion of gas and liquid stool ('squirt sign'). A contrast enema reveals a narrow rectosigmoid segment with significant dilation of the proximal colon. What is the definitive diagnostic procedure to confirm Hirschsprung disease?

Answer and explanation

Correct answer: A. Rectal suction biopsy demonstrating absence of ganglion cells

  1. Step 1: Hirschsprung disease (congenital aganglionic megacolon) results from the failure of neural crest cells to migrate craniocaudally into the distal bowel wall.
  2. Step 2: The aganglionic segment remains tonically contracted, causing functional distal bowel obstruction, failure to pass meconium in the first 48 hours, and bilious vomiting.
  3. Step 3: Rectal suction biopsy taken at least 2 cm above the dentate line is the definitive gold standard test, demonstrating complete absence of ganglion cells and hypertrophied nerve bundles with acetylcholinesterase staining.
Answer
Rectal suction biopsy demonstrating absence of ganglion cells.
Why not the others: 'Full colonoscopy' cannot evaluate the intramural neural plexuses and risks perforation; 'RET proto-oncogene testing' identifies familial predisposition but cannot confirm the histopathologic diagnosis; 'Pelvic CT' shows bowel distension but lacks microscopic diagnostic capability.

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