What is the differential diagnosis and appropriate workup for a 35-day-old baby presenting with biliary vomiting?

Bilious Vomiting in a 35-Day-Old Infant

Immediate Clinical Significance

Bilious vomiting in a 35-day-old infant is a surgical emergency until proven otherwise and requires immediate evaluation to exclude midgut volvulus, which can cause intestinal necrosis within hours. 1

The presence of bile in vomitus indicates obstruction distal to the ampulla of Vater, and while only 20% of cases within the first 72 hours represent midgut volvulus, the catastrophic consequences of missing this diagnosis—including vascular compromise, transmural intestinal ischemia, massive bowel resection, short gut syndrome, or death—mandate urgent action. 1

Differential Diagnosis

Most Critical to Exclude First

• Midgut malrotation with volvulus: The twisting of mesentery around the superior mesenteric artery compromises blood flow to the entire midgut, leading to venous congestion, arterial compromise, and potentially irreversible necrosis within hours. 1

Other Surgical Causes (in order of likelihood at 35 days)

• Intestinal atresia (duodenal, jejunal, ileal): Common congenital malformations causing mechanical obstruction. 1, 2
• Hirschsprung disease: Functional obstruction from absent ganglion cells. 1, 3
• Annular pancreas: Congenital duodenal obstruction. 1, 4
• Meconium ileus: Distal small bowel obstruction from inspissated meconium. 2

Non-Surgical Causes

• Sepsis/meningitis: Can present with bilious vomiting at any age without anatomic obstruction. 1
• Increased intracranial pressure: Neurologic causes should be considered. 1
• Metabolic disorders: Can mimic surgical obstruction. 1
• Polycythemia: Identified in some cases without anatomic abnormality. 3
• No identifiable cause: In one series, 20 of 39 infants with normal upper GI studies had no diagnosis identified. 3

Immediate Diagnostic Workup

Step 1: Immediate Stabilization

• Place nasogastric or orogastric tube immediately to decompress the stomach before any imaging. 2

Step 2: Plain Abdominal Radiograph (First Study)

• Obtain immediately as the initial imaging study. 1, 5, 2
• Look for:
  • "Double bubble" sign (duodenal obstruction/atresia) 1
  • Multiple dilated bowel loops with absent or decreased distal gas 1
  • Air-fluid levels suggesting obstruction 2

Critical caveat: Normal abdominal radiographs do NOT exclude malrotation or volvulus—clinical suspicion based on bilious vomiting alone mandates proceeding to upper GI study regardless of radiograph findings. 1

Step 3: Upper GI Contrast Series (Definitive Study)

• Perform urgently if bilious vomiting is present, even with normal plain films. 1, 5
• This is the gold standard with 96% sensitivity for detecting malrotation. 1
• The critical finding is abnormal position of the duodenojejunal junction (ligament of Treitz), which indicates malrotation. 1, 5
• Meticulous technique is essential to avoid false results from redundant duodenum or bowel distension. 1
• False-positive rate: 10-15%; false-negative rate: up to 7%. 1

Step 4: Surgical Consultation

• Immediate pediatric surgical consultation is mandatory upon confirmation of bilious vomiting, given the potential for volvulus to compromise intestinal vascularization within hours. 5
• Proceed directly to surgery if upper GI series confirms malrotation/volvulus. 1

Studies NOT to Perform Initially

• Contrast enema: Reserved for distal bowel obstruction scenarios; has approximately 20% false-negative rate for malrotation, making it inferior to upper GI series. 1
• Ultrasound: Has 21% false-positive and 2-3% false-negative rates for malrotation and should not delay upper GI series. 1
• Endoscopy: Has no role in acute evaluation of intestinal obstruction. 5

Additional Workup if Upper GI Series is Normal

If upper GI contrast study is normal (which occurred in 39 of 45 infants in one series), consider: 3

• Sepsis workup: Blood cultures, complete blood count, C-reactive protein, lumbar puncture if clinically indicated. 3
• Metabolic screening: If no anatomic cause identified. 1
• Neuroimaging: If neurologic signs present or increased intracranial pressure suspected. 1, 3
• Complete blood count: To evaluate for polycythemia. 3

Common Pitfalls to Avoid

• Do not be falsely reassured by normal plain radiographs—up to 96% sensitivity means 4% of malrotations can have normal films. 1
• Do not delay upper GI series based on normal initial radiographs or attempt ultrasound first. 1
• Do not confuse with pyloric stenosis, which presents with non-bilious projectile vomiting typically between 2 weeks to 3 months of age. 5
• Do not assume all bilious vomiting is surgical—in one series, only 26.6% required laparotomy, but all required evaluation to exclude surgical causes. 6