Typical X-ray Findings in Congenital Megacolon (Hirschsprung Disease)
Plain abdominal radiographs in newborns with Hirschsprung disease typically show numerous dilated bowel loops with an absence or paucity of distal gas, indicating a distal bowel obstruction pattern. 1
Primary Radiographic Features
The initial plain abdominal X-ray serves as the first-line imaging study and demonstrates several characteristic findings: 2
- Dilated bowel loops with air-fluid levels throughout the abdomen 2
- Absence or marked reduction of gas in the distal colon and rectum - this is a key distinguishing feature 1
- Multiple distended loops indicating functional obstruction at the distal bowel 2
Important Limitations of Plain Radiographs
Plain radiographs alone cannot definitively diagnose Hirschsprung disease and have significant limitations: 3, 4
- Cannot differentiate between causes of distal obstruction (Hirschsprung disease, meconium plug, ileal atresia, meconium ileus all appear similar) 1, 4
- Serve primarily as a screening tool to identify that obstruction exists, not to determine the specific etiology 3
- Must be followed by contrast enema for definitive diagnosis when distal obstruction is suspected 3, 4
Next Step After Abnormal X-ray
Contrast enema is the diagnostic imaging procedure of choice following abnormal plain films, as it can demonstrate the transition zone between the narrow aganglionic distal segment and the dilated proximal colon. 4
The contrast enema has approximately 80% sensitivity for detecting the transition zone but carries a 20% false-negative rate, meaning it screens for but does not definitively exclude Hirschsprung disease. 3 Rectal biopsy remains the gold standard for confirmation. 4
Critical Pitfall to Avoid
Never assume Hirschsprung disease and proceed directly to rectal biopsy based solely on plain radiographs - the clinical and radiographic presentation is identical for multiple causes of distal obstruction including meconium plug syndrome, ileal atresia, and meconium ileus. 4 The contrast enema is both diagnostic and potentially therapeutic (can evacuate meconium plugs). 4
Ultrasound Has No Role
Ultrasound is not supported by evidence for evaluating suspected distal obstruction in neonates and should not be used in this clinical scenario. 4, 2