What is the differential diagnosis for a 2-week-old infant presenting with green mucus in vomit?

Differential Diagnosis for Green Vomitus in a 2-Week-Old Infant

Green (bilious) vomiting in a 2-week-old infant is a surgical emergency until proven otherwise, with midgut volvulus being the most critical life-threatening diagnosis that requires immediate evaluation and potential urgent surgery. 1

Critical Context

Bilious vomiting indicates obstruction distal to the ampulla of Vater and represents a surgical emergency at any age. 1, 2 In the first 72 hours of life, 20% of infants with bilious vomiting have midgut volvulus, which requires urgent surgical intervention. 3, 1

Primary Differential Diagnoses

Surgical Emergencies (Require Immediate Evaluation)

Midgut Volvulus with Malrotation

• Accounts for 20% of bilious vomiting cases in neonates within first 72 hours 3, 1
• Most critical diagnosis to exclude due to risk of bowel necrosis 1
• Requires immediate imaging and surgical consultation 1

Duodenal Atresia

• Most common cause of proximal bowel obstruction 3, 1
• Presents with bilious vomiting and gastric distension 3
• Classic "double bubble" sign on abdominal radiograph with no distal gas 3
• Note: 15% of proximal obstructions may present with nonbilious vomiting initially 3

Jejunal Atresia

• Presents with "triple bubble" sign with absent distal gas 3, 1
• Vomiting typically begins in first 2 days after birth 3
• Multiple atresias occur in approximately 15% of cases 3

Intestinal Atresia (Distal)

• Presents with multiple distended bowel loops 3
• No passage of meconium typical 3
• Results in microcolon due to lack of intestinal contents 3

Intussusception

• Can present with bilious vomiting indicating progression to obstruction 2
• Associated with crampy, intermittent abdominal pain (inconsolable crying, drawing up legs) 2
• "Currant jelly" stools indicate mucosal damage 1, 2
• Palpable abdominal mass may be present 4

Other Structural Causes

Duodenal Web

• Rare cause of duodenal obstruction 3
• Presents similarly to duodenal atresia 3

Internal Hernia

• Rare cause of proximal obstruction 3

Obstructing Duplication Cyst

• Rare cause of duodenal obstruction 3

Functional/Medical Causes

Meconium Plug Syndrome

• Distal obstruction pattern on radiograph 3
• May require therapeutic enema 3
• Accounts for 11% of bilious vomiting in first 72 hours 3

Meconium Ileus

• Distal obstruction pattern 3
• May respond to therapeutic enema 3

Hirschsprung Disease

• Distal obstruction pattern 3
• May require rectal biopsy for diagnosis 3

Necrotizing Enterocolitis

• Life-threatening condition in neonates 5
• Presents with bilious vomiting, abdominal distension, bloody stools 5

Sepsis/Meningitis

• Can present with vomiting as part of systemic illness 5
• Look for toxic appearance, altered sensorium, fever or hypothermia 5

Inborn Errors of Metabolism

• Life-threatening metabolic conditions 5
• May present with vomiting, lethargy, poor feeding 5

Congenital Adrenal Hypoplasia

• Can present with vomiting in first weeks of life 5
• Associated with electrolyte abnormalities 5

Immediate Diagnostic Approach

Initial Imaging: Abdominal Radiograph

• First-line imaging for any bilious vomiting 3, 1
• Look for "double bubble" (duodenal obstruction), "triple bubble" (jejunal obstruction), or multiple air-fluid levels suggesting obstruction 1
• Assess for proximal versus distal obstruction pattern 3

Subsequent Imaging Based on Radiograph Findings:

• Classic double/triple bubble with no distal gas: Surgical consultation without further imaging typically needed 3
• Distal obstruction pattern: Contrast enema is diagnostic procedure of choice to differentiate structural from functional causes 3
• Nonclassic pattern or concern for volvulus: Upper GI series or ultrasound may be indicated 3

Critical Red Flags and Pitfalls

Never dismiss bilious vomiting as benign gastroenteritis - this is a surgical emergency until proven otherwise. 1

Key red flag signs requiring immediate evaluation: 5, 6

• Bilious or bloody vomiting
• Altered sensorium or toxic/septic appearance
• Severe dehydration
• Abdominal distension or signs of obstruction
• Inconsolable crying or excessive irritability

Common pitfall: Approximately 15% of proximal bowel obstructions present with nonbilious vomiting initially, which can delay diagnosis. 3 Maintain high suspicion even if vomiting is not consistently bilious.

Immediate management priorities: 5

• Stop oral feeds immediately
• Nasogastric tube decompression for bilious vomiting
• IV fluid resuscitation if dehydrated
• Urgent surgical consultation
• Do not delay imaging or surgical evaluation