What is the pathology of bilious vomiting?

Pathology of Bilious Vomiting

Bilious vomiting indicates intestinal obstruction distal to the ampulla of Vater, where bile enters the duodenum, and represents a surgical emergency until proven otherwise. 1, 2

Anatomic Basis

The presence of bile in vomitus occurs when intestinal contents proximal to an obstruction are forced retrograde back through the stomach. The critical anatomic landmark is the ampulla of Vater—bile in vomitus definitively localizes the obstruction point to somewhere distal to this structure. 2 This distinguishes bilious from non-bilious vomiting, which occurs with obstructions proximal to the ampulla (such as pyloric stenosis). 1

Age-Specific Pathologic Causes

Neonates (First 72 Hours of Life)

In neonates presenting within the first 72 hours, 20% of bilious vomiting cases represent midgut volvulus, making this the most critical diagnosis to exclude. 2 The pathologic mechanisms include:

• Intestinal atresia (duodenal, jejunal, or ileal): Complete congenital obstruction from failed recanalization during embryologic development 2, 3
• Midgut malrotation with volvulus: Abnormal intestinal rotation during fetal development creates a narrow mesenteric base, predisposing to twisting around the superior mesenteric artery with resultant vascular compromise and intestinal necrosis within hours 4, 1
• Hirschsprung disease: Absence of ganglion cells in the distal colon causing functional obstruction 2, 5
• Meconium ileus: Inspissated meconium obstructing the terminal ileum, often associated with cystic fibrosis 3
• Necrotizing enterocolitis: Ischemic bowel necrosis with pneumatosis intestinalis 3

Older Infants and Children

• Intussusception: Telescoping of bowel (typically ileocolic) causing obstruction and vascular compromise, classically presenting with crampy pain, "currant jelly" stools, and progression from non-bilious to bilious vomiting 1, 2
• Internal hernias: Particularly post-surgical (e.g., after gastric bypass) 2

Non-Surgical Pathology

While surgical obstruction must be excluded first, approximately 50% of neonates with bilious vomiting have no identifiable surgical cause after complete evaluation. 6 Non-obstructive etiologies include:

• Sepsis: Ileus from systemic infection (identified in 27% of non-surgical cases) 6
• Polycythemia: Hyperviscosity causing intestinal hypoperfusion 6
• Neurologic disorders: Such as polymicrogyria causing dysmotility 6
• Meconium plug syndrome: Functional obstruction without anatomic abnormality 6

Critical Pathophysiologic Consequence

The most urgent pathologic concern is midgut volvulus, where twisting of the mesentery around the superior mesenteric artery compromises blood flow to the entire midgut. 4, 1 Without surgical detorsion within hours, this progresses to:

1. Venous congestion
2. Arterial compromise
3. Transmural intestinal ischemia
4. Necrosis requiring massive bowel resection
5. Short gut syndrome or death

This explains why bilious vomiting at any age requires immediate gastric decompression with nasogastric tube placement and urgent imaging evaluation, typically starting with plain abdominal radiograph followed by upper GI contrast series. 1, 3 The upper GI series has 96% sensitivity for detecting malrotation by demonstrating abnormal position of the duodenojejunal junction (ligament of Treitz). 1

Common Diagnostic Pitfall

Normal abdominal radiographs do NOT exclude malrotation or volvulus—in one series, only 44% of infants requiring surgery for bilious vomiting had definitively positive plain films. 4 Therefore, clinical suspicion based on bilious vomiting alone mandates proceeding to upper GI contrast study regardless of radiograph findings. 4, 1