What is the diagnostic approach for intestinal obstruction in children under 6 months?

Diagnostic Approach for Intestinal Obstruction in Infants Under 6 Months

Begin with plain abdominal radiographs as the first-line imaging study, followed by targeted fluoroscopic studies based on the suspected level of obstruction—upper GI series for proximal/midgut pathology and contrast enema for distal obstruction. 1

Clinical Presentation and Initial Assessment

Cardinal Signs to Identify

The four critical findings that indicate intestinal obstruction in neonates are: 2

• Maternal polyhydramnios (suggests high obstruction preventing fetal swallowing) 2
• Bilious vomiting (ominous sign requiring urgent evaluation for malrotation/volvulus) 1
• Failure to pass meconium within first 24 hours of life 2
• Abdominal distention (may progress to respiratory distress and cardiovascular collapse) 2

Age-Specific Differential Diagnosis

First 2 days of life: 1

• Malrotation with or without midgut volvulus (20% of bilious vomiting cases) 1
• Intestinal atresia (duodenal, jejunal, ileal, or colonic) 1
• Annular pancreas 1
• Meconium ileus or meconium plug syndrome 1, 3
• Hirschsprung disease 1

Beyond neonatal period (up to 6 months): 1

• Hypertrophic pyloric stenosis (palpable "olive" on examination) 1
• Intussusception (unusual before 3 months but presents with crampy pain, bloody stools, lethargy) 1, 4

Imaging Algorithm

Step 1: Plain Abdominal Radiographs (Initial Study)

Always obtain plain films first—they have 74% sensitivity and guide subsequent imaging decisions. 1, 5

Key radiographic patterns: 1, 6

• "Double bubble" sign = duodenal atresia (stomach + duodenal dilation with no distal gas) 1, 6
• "Triple bubble" sign = jejunal atresia 6
• Multiple dilated loops with absent/decreased distal gas = distal obstruction (ileal atresia, Hirschsprung, meconium ileus) 1, 6
• Few distended loops or nonclassic double bubble with some distal gas = requires upper GI series to exclude malrotation 1
• Normal bowel gas pattern with bilious vomiting = malrotation with incomplete obstruction until proven otherwise 1

Step 2: Targeted Fluoroscopic Studies

For Suspected Proximal/Midgut Obstruction (Bilious Vomiting with Nonclassic Findings)

Upper GI series is the reference standard for diagnosing malrotation and midgut volvulus. 1, 5

• Sensitivity: 96% for detecting malrotation by identifying abnormal position of duodenojejunal junction (ligament of Treitz) 1, 5
• Critical pitfall: False-negatives (7 cases in 229 patients) and false-positives (10-15%) can occur due to redundant duodenum, bowel distension, or jejunal position variations—meticulous technique is essential 1
• Urgency: Midgut volvulus requires immediate surgery; do not delay this study when suspected 1

For Suspected Distal Obstruction (Multiple Dilated Loops, Absent Distal Gas)

Contrast enema is the diagnostic procedure of choice for distal obstruction. 1

• Differentiates between: 1
  • Functional abnormalities requiring observation only (meconium plug)
  • Structural lesions requiring surgery (ileal atresia, colonic atresia)
  • Therapeutic conditions (meconium ileus—enema may be therapeutic)
  • Hirschsprung disease requiring rectal biopsy
• Microcolon appearance indicates lack of intestinal contents passing through bowel, seen in atresias 1, 6

Important limitation: Contrast enema is less accurate than upper GI series for malrotation (20% false-negative rate, 15% false-positive rate due to mobile cecum) 1

Step 3: Ultrasound (Limited Role)

Current evidence does not support ultrasound as a primary diagnostic modality for intestinal obstruction in this age group. 1, 6

• No literature supports ultrasound as initial imaging before plain radiographs 1, 6
• Limited accuracy for malrotation: 21% false-positive and 2-3% false-negative rates when evaluating SMV/SMA relationship 1
• Technical limitations: Bowel gas obscures SMA/SMV in up to 17% of cases 1
• May be useful for pyloric stenosis diagnosis (hypertrophied pyloric muscle measurement) in older infants 1

Critical Management Principles

Timing and Urgency

• Delay in diagnosis is the major risk factor for mortality, especially with midgut volvulus 7
• Bilious vomiting in first 72 hours of life: 20% have midgut volvulus requiring urgent surgery 1
• Neonates deteriorate rapidly when obstruction is unrecognized—prompt imaging and surgical consultation are essential 3, 7

Resuscitation Before Imaging

Concomitant resuscitation must occur during diagnostic workup: 2

• Volume resuscitation with IV fluids and electrolyte correction 2
• Nasogastric decompression 2
• Ventilatory support if respiratory distress present 2

When to Proceed Directly to Surgery

Skip additional imaging and proceed to exploration when: 1

• Peritonitis on examination
• Signs of strangulation or ischemia
• Symptoms present >5 days with severe obstruction on plain films 4

Prognosis Factors

• Overall mortality should be <5% with specialized neonatal care 7
• Prematurity is not a significant risk factor for poor outcome 7
• Major risk factors: Delay in diagnosis/intervention, chromosomal abnormalities, and associated major congenital anomalies (especially cardiac) 3, 7