Rectal Biopsy is the Definitive Diagnostic Test
For a 1-month-old infant presenting with constipation since birth, abdominal distension, and bilious vomiting—classic features of Hirschsprung disease—rectal biopsy (Option B) has the highest diagnostic value as it provides definitive histopathological confirmation and is the gold standard for diagnosis. 1
Diagnostic Algorithm for Suspected Hirschsprung Disease
Initial Imaging: Plain Radiograph First
- Plain abdominal radiographs should be obtained first in all infants with suspected bowel obstruction, as they demonstrate dilated bowel loops, air-fluid levels, and the presence or absence of distal gas 2, 3
- However, plain X-rays alone cannot definitively diagnose or exclude Hirschsprung disease 4
Second-Line Imaging: Contrast Enema
- The American College of Radiology recommends contrast enema as the diagnostic imaging procedure of choice for suspected distal bowel obstruction, as it can differentiate between functional abnormalities, surgical pathologies, and conditions requiring therapeutic intervention 4
- Contrast enema can demonstrate the transition zone between the narrow aganglionic segment and dilated proximal colon characteristic of Hirschsprung disease 4
- However, a normal contrast enema does NOT exclude Hirschsprung disease—the sensitivity is only 52.3% 5
- The American College of Radiology explicitly advises against assuming Hirschsprung disease and proceeding directly to rectal biopsy without contrast enema, as the clinical presentation is identical for multiple causes of distal obstruction 4
Definitive Diagnosis: Rectal Biopsy
- Rectal biopsy is the gold standard with 100% sensitivity and specificity for diagnosing Hirschsprung disease 5
- Diagnosis ultimately rests upon histopathological evaluation demonstrating absence of ganglion cells in the rectal submucosa 1
- Ancillary tests such as acetylcholinesterase histochemistry or calretinin immunohistochemistry complement the diagnosis 1
- In infants with classic symptoms (delayed meconium passage, abdominal distension, bilious vomiting), pediatric surgeons achieve higher rates of adequate and positive biopsies compared to gastroenterologists 6
Role of Anorectal Manometry
- Anorectal manometry has 95% sensitivity and 90.24% specificity for neonatal diagnosis of Hirschsprung disease by demonstrating absence of the recto-anal inhibitory reflex (RAIR) 5
- It serves as a useful screening tool prior to rectal biopsy in centers with access to pediatric gastroenterology services 5
- However, manometry is operator-dependent and less readily available than imaging or biopsy 7
Why Ultrasound is NOT Appropriate
- The American College of Radiology states that ultrasound has no role in evaluating neonates with suspected distal obstruction, as there is no relevant literature supporting its use in this clinical scenario 4, 2
- Ultrasound cannot diagnose Hirschsprung disease or differentiate it from other causes of distal obstruction 4
Clinical Context Supporting Rectal Biopsy
Your patient has the classic triad present in 18% of Hirschsprung disease cases: delayed passage of meconium (constipation since birth), vomiting (bilious), and abdominal distension 8. These features, when present together, strongly indicate Hirschsprung disease and warrant definitive diagnosis 8.
Critical Pitfall to Avoid
While contrast enema is recommended as the initial diagnostic imaging procedure 4, the question asks which test has the highest diagnostic value. A normal contrast enema does not exclude Hirschsprung disease (sensitivity only 52.3%), whereas rectal biopsy has 100% sensitivity and specificity 5. Therefore, rectal biopsy provides the highest diagnostic value and definitive diagnosis 1.