Abdominal X-ray is the Most Appropriate Initial Investigation
For a child presenting with greenish (bilious) vomiting and abdominal pain, an abdominal X-ray should be obtained immediately as the first imaging study. 1, 2
Clinical Significance of Bilious Vomiting
Greenish vomiting indicates bilious emesis, which signals obstruction distal to the ampulla of Vater and represents a surgical emergency until proven otherwise. 2, 3 This presentation raises immediate concern for life-threatening conditions including:
- Malrotation with midgut volvulus - can cause intestinal necrosis within hours if not promptly diagnosed 2
- Intussusception - may present with bilious vomiting as obstruction progresses 2
- Other forms of intestinal obstruction requiring urgent surgical evaluation 2, 4
Diagnostic Algorithm
Step 1: Abdominal X-ray (Initial Study)
The abdominal radiograph is the crucial first step to identify signs of intestinal obstruction, including: 2, 5
- Dilated bowel loops
- Air-fluid levels
- Pattern of gas distribution
- Double bubble or triple bubble sign (suggesting proximal obstruction)
- Distal bowel gas pattern
The American College of Radiology guidelines emphasize that abdominal radiograph is the appropriate initial imaging to detect obstruction patterns, even though the fundamental principle remains that bilious vomiting is a surgical emergency. 1, 2
Step 2: Upper GI Contrast Series (If Obstruction Confirmed)
After the initial radiograph, an upper GI series is usually appropriate for children with bilious vomiting to evaluate for malrotation and midgut volvulus, with 96% sensitivity for detecting malrotation. 2 The upper GI series directly visualizes the duodenojejunal junction (ligament of Treitz), with abnormal positioning indicating malrotation. 2
For infants older than 2 days with bilious vomiting, fluoroscopy UGI series is usually appropriate as the next imaging study, particularly when radiographs show nonclassic findings or normal bowel gas patterns. 1
Why Not the Other Options?
Lower GI Contrast (Contrast Enema) - Inappropriate
Contrast enema is NOT appropriate for initial evaluation of bilious vomiting. 2 It is reserved specifically for suspected distal bowel obstruction identified on initial radiographs, not as a first-line study. 1, 2 The American College of Radiology recommends contrast enema only after radiographs demonstrate a distal obstruction pattern. 1
Upper GI Contrast as Initial Study - Less Optimal
While upper GI series is excellent for diagnosing malrotation, starting directly with upper GI contrast without first obtaining a plain radiograph misses the critical initial step of identifying the obstruction pattern and severity. 2, 5 The abdominal X-ray provides essential information about whether obstruction is proximal versus distal, which guides subsequent imaging choices. 1
Critical Management Points
Immediate actions required alongside imaging: 2, 6
- Intravenous access and fluid resuscitation
- Immediate pediatric surgical consultation upon confirmation of bilious vomiting
- NPO status (nothing by mouth)
- Nasogastric tube decompression if obstruction confirmed
Common Pitfalls to Avoid
Failing to recognize bilious vomiting as a surgical emergency is the most dangerous error - in neonates, midgut volvulus represents 20% of cases with bilious vomiting and can lead to complete intestinal necrosis within hours. 3
Do not confuse this presentation with pyloric stenosis, which presents with NON-bilious projectile vomiting in infants 2 weeks to 3 months old and would warrant ultrasound as the initial study. 2, 7 The presence of bile (greenish color) immediately excludes pyloric stenosis from consideration.
Do not delay imaging for extensive laboratory workup - while labs may be obtained, the abdominal X-ray should be performed urgently and not delayed. 4, 8