What is the differential diagnosis for a patient presenting with bilious vomiting, considering their age, medical history, and physical examination findings?

Differential Diagnosis of Bilious Vomiting

Bilious vomiting represents intestinal obstruction distal to the ampulla of Vater until proven otherwise and demands immediate evaluation, with malrotation with midgut volvulus being the most critical diagnosis to exclude due to risk of intestinal necrosis within hours. 1, 2

Age-Specific Differential Diagnoses

Neonates (First Week of Life)

Critical surgical emergencies:

• Malrotation with midgut volvulus - The most urgent diagnosis, as twisting around the superior mesenteric artery causes vascular compromise leading to transmural intestinal ischemia and potential necrosis requiring massive bowel resection or death 1
• Intestinal atresia (duodenal, jejunal, ileal) - Presents with bilious vomiting within first 2 days, abdominal distension, and failure to pass meconium 3, 4
• Annular pancreas - Congenital anomaly causing duodenal obstruction 3
• Meconium ileus - Associated with cystic fibrosis 3, 5
• Hirschsprung disease - Functional obstruction from absent ganglion cells 3, 1
• Necrotizing enterocolitis - Particularly in premature infants 5

Key clinical point: In neonates, 20% of bilious vomiting cases within the first 72 hours represent midgut volvulus 1

Infants (Beyond Newborn Period)

• Intussusception - Presents with crampy intermittent abdominal pain (inconsolable crying, drawing up legs), progression to bloody "currant jelly" stools, and lethargy 3, 1, 6
• Hypertrophic pyloric stenosis - Though typically non-bilious, can present with bilious vomiting if severe; palpable "olive" mass 3
• Gastroenteritis - Viral etiology with sudden onset, mild fever, diarrhea, and short duration 3
• Formula intolerance 3

All Ages

Non-gastrointestinal causes to consider:

• Sepsis/meningitis - Fever, toxic appearance, altered mental status 3, 7
• Increased intracranial pressure - From tumor, trauma, or hydrocephalus; presents with enlarging head circumference, bulging fontanelle, neurologic signs 3
• Metabolic disorders - Phenylketonuria, hyperammonemia, maple syrup urine disease, galactosemia, adrenocortical hyperplasia 3
• Urinary tract obstruction - Obstructive uropathy 7

Physical Examination Red Flags

Immediate surgical consultation required if present:

• Bilious or bloody vomiting 7
• Abdominal distension combined with bilious vomiting (strongly suggests proximal bowel obstruction) 1
• Altered sensorium or toxic/septic appearance 7
• Inconsolable cry or excessive irritability 7
• Severe dehydration 7
• Bent-over posture 7

Diagnostic Approach Algorithm

Step 1: Immediate stabilization

• Place nasogastric tube for gastric decompression 7, 5
• Assess airway, breathing, circulation 7
• Evaluate hydration status 7

Step 2: Initial imaging

• Abdominal radiograph first - Look for double bubble sign (duodenal obstruction), triple bubble sign (jejunal atresia), multiple dilated bowel loops with air-fluid levels, or absent/decreased distal gas 1, 6, 5
• 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, 6

Step 3: Definitive imaging

• Upper GI contrast series - The definitive study with 96% sensitivity for detecting malrotation; identifies abnormal position of duodenojejunal junction and presence of midgut volvulus 1, 6
• Proceed directly to surgery if malrotation/volvulus confirmed 1

Step 4: Alternative imaging (limited roles)

• Ultrasound - Has 21% false-positive and 2-3% false-negative rates for malrotation; should not delay upper GI series 1
• Contrast enema - Reserved for distal bowel obstruction scenarios; has 20% false-negative rate for malrotation, making it inferior to upper GI series 1

Common Pitfalls to Avoid

• Never delay imaging based on normal initial radiographs - Up to 15% of upper GI studies may be inconclusive, requiring adjunctive techniques or repeat studies 8
• Do not confuse with gastroesophageal reflux - GER presents with non-bilious regurgitation in well-appearing infants with normal weight gain 3
• Do not mistake for pyloric stenosis - HPS presents with non-bilious projectile vomiting in infants 2 weeks to 3 months old 6
• Avoid routine laboratory screening - Investigations are only required in children with dehydration or red flag signs 7