What could cause abdominal distension, diarrhoea, and multiple air‑fluid levels on an erect abdominal X‑ray?

Abdominal Distension with Diarrhoea and Air-Fluid Levels: Clinical Interpretation

Yes, this combination is possible and typically indicates either severe small intestinal dysmotility (pseudo-obstruction), mechanical bowel obstruction with partial patency, or colonic perforation with peritonitis. The presence of air-fluid levels on erect abdominal X-ray combined with diarrhoea creates a diagnostic paradox that requires systematic evaluation to distinguish between these entities.

Primary Differential Diagnoses

Chronic Intestinal Pseudo-Obstruction (CIPO)

• Myopathic CIPO characteristically presents with abdominal distension, alternating diarrhoea and constipation, and dilated small and large bowel on plain radiographs 1
• The diarrhoea in this context represents overflow around dilated, dysmotile bowel segments rather than true hypermotility 1
• Plain abdominal radiographs show dilated small and large bowel with multiple air-fluid levels, mimicking mechanical obstruction 1
• Neuropathic variants may present similarly but often have less prominent distension and may show normal plain films despite severe symptoms 1

Mechanical Small Bowel Obstruction with Partial Patency

• Air-fluid levels of differential height within the same bowel loop and mean air-fluid level width ≥25 mm on upright films are the most predictive findings for high-grade mechanical obstruction 2
• When obstruction is incomplete, liquid stool may pass through the narrowed segment while proximal bowel remains distended 2, 3
• The presence of multiple air-fluid levels with bowel distension ratio >1.0 for small bowel indicates mechanical obstruction requiring surgical evaluation 3

Colonic Perforation with Peritonitis

• Free intraperitoneal air combined with air-fluid levels and abdominal distension indicates perforation requiring immediate surgical intervention 1, 4
• Diarrhoea in this setting may represent inflammatory exudate or pre-perforation colitis 1
• CT scan demonstrates distant free air, air-fluid levels, and peritoneal fluid collections 4

Critical Diagnostic Algorithm

Step 1: Assess Clinical Context

• Examine for the "gush sign" on digital rectal examination—passage of examining finger through spastic segment followed by gush of liquid stool is pathognomonic for distal functional or anatomic obstruction 5
• Evaluate medication history: opioids and anticholinergics (especially cyclizine) cause pseudo-obstruction that mimics mechanical obstruction 5
• Screen for systemic causes: hypothyroidism, diabetes mellitus, coeliac disease, and Chagas disease (in endemic areas) all produce dysmotility with this radiographic pattern 1, 5

Step 2: Interpret Radiographic Findings

• Multiple air-fluid levels with distended bowel loops and absence of distal colonic gas constitutes the pathognomonic triad for bowel obstruction 4
• Air-fluid levels require horizontal beam imaging (upright or decubitus); supine films cannot demonstrate fluid levels 4
• Plain radiography has 92% positive predictive value for perforation during diagnostic procedures but only 45% for therapeutic procedures 1

Step 3: Obtain CT Imaging

• CT scan with IV contrast is the gold standard when clinical suspicion persists despite radiographic findings 4
• CT has approximately 90% accuracy in predicting strangulation and need for urgent surgery 4
• Look for transition points (mechanical obstruction), diffuse dilation without transition (pseudo-obstruction), or free air with fluid collections (perforation) 1, 4

Step 4: Laboratory Assessment

• Obtain white blood cell count, C-reactive protein, and procalcitonin (if >12 hours from symptom onset) to assess for perforation-associated infection 1
• Check electrolytes (especially potassium and magnesium), thyroid function, glucose, and coeliac serology 1
• Consider Chagas serology in patients from endemic areas (Latin America) 5

Management Implications

Immediate Surgical Intervention Required

• Patients with air-fluid levels plus signs of peritonitis require immediate surgical exploration 4
• Free intraperitoneal air with air-fluid levels contraindicates non-operative management, particularly in elderly patients 4
• Delayed surgical intervention beyond 72 hours significantly increases morbidity and mortality 6

Medical Management Appropriate

• Pseudo-obstruction without perforation is managed by discontinuing causative medications, treating underlying endocrine/autoimmune disorders, and nutritional optimization 1, 5
• Severe malnutrition (BMI <18.5 kg/m² or >10% unintended weight loss) independently impairs motility and must be corrected before attributing symptoms solely to dysmotility 5
• Chronic opioid use requires supervised withdrawal with pain-specialist involvement before definitive diagnosis 5

Common Pitfalls to Avoid

• Do not assume diarrhoea excludes mechanical obstruction—liquid stool may pass through partial obstructions while proximal bowel remains obstructed 1, 2
• Do not rely solely on plain radiography for perforation diagnosis—CT is required to exclude abscess, fistula, or contained perforation 4
• Do not attribute symptoms to functional disorders without excluding Chagas disease in patients from endemic areas—this parasitic infection destroys myenteric plexus neurons and causes acquired megacolon 5
• Ultrasound can demonstrate free fluid between bowel loops, which indicates high-grade obstruction requiring immediate surgery rather than medical therapy 7