Differentiating and Managing Ileus versus Small Bowel Obstruction
CT imaging is the most accurate diagnostic tool to differentiate between ileus and small bowel obstruction, with sensitivity and specificity approaching 100%, and should be the primary diagnostic modality when the distinction is clinically important. 1
Clinical Differentiation
History and Physical Examination Findings
| Feature | Small Bowel Obstruction (SBO) | Ileus/Pseudo-obstruction |
|---|---|---|
| Pain | Colicky, cramping, intermittent | Diffuse, constant, less severe |
| Vomiting | Early, bilious | Later onset |
| Previous surgery | Strong predictor (85% sensitivity, 78% specificity) [2] | Often post-operative, trauma, metabolic disorders |
| Bowel sounds | High-pitched, tinkling | Diminished or absent |
| Abdominal distention | Asymmetric | Symmetric, diffuse |
| Onset | Acute | Gradual |
Key Risk Factors
Small Bowel Obstruction:
- Previous abdominal surgery (adhesions account for 55-75% of cases) 2
- Hernias (15-25% of cases)
- Malignancies (5-10% of cases)
Ileus/Pseudo-obstruction:
- Recent surgery
- Medications (opioids, anticholinergics)
- Electrolyte abnormalities
- Severe systemic illness
- Trauma 3
Diagnostic Approach
Initial Imaging
Plain Abdominal Radiography:
CT Abdomen/Pelvis (preferred):
- Gold standard with >90% diagnostic accuracy 2
- Differentiates SBO from ileus with 100% sensitivity and specificity 1
- Identifies:
- Transition point (hallmark of mechanical obstruction)
- Cause of obstruction
- Complications (ischemia, perforation)
- Closed-loop obstruction
- No oral contrast needed in suspected high-grade obstruction 2
Ultrasound:
- Emerging role with high accuracy (+LR 14.1) 4
- Particularly useful in pregnancy or when CT is contraindicated
- Can identify dilated loops and transition points
Water-soluble Contrast Studies:
- Both diagnostic and potentially therapeutic
- Appearance of contrast in colon within 24 hours predicts successful non-operative management (96% sensitivity, 98% specificity) 2
Management Algorithm
1. Initial Assessment and Stabilization
- IV fluid resuscitation
- Correct electrolyte abnormalities
- NPO status
- Nasogastric tube decompression
- Pain management
2. For Ileus/Pseudo-obstruction:
- Identify and treat underlying cause
- Discontinue medications that decrease motility
- Correct metabolic/electrolyte abnormalities
- Consider neostigmine for colonic pseudo-obstruction 3
- Supportive care until resolution
- Monitor for signs of improvement (passage of flatus/stool)
3. For Small Bowel Obstruction:
Conservative management for partial/low-grade obstruction:
- Nasogastric decompression
- IV fluids
- Serial abdominal examinations
- Water-soluble contrast study may help predict resolution
Surgical intervention indicated for:
- Complete obstruction
- Signs of strangulation/ischemia
- Closed-loop obstruction
- Failed conservative management (48-72 hours)
- Hernia with obstruction
Red Flags Requiring Immediate Surgical Intervention
- Peritoneal signs
- Fever, tachycardia, leukocytosis
- CT findings of ischemia:
- Abnormal bowel wall enhancement
- Pneumatosis intestinalis
- Portal venous gas
- Mesenteric edema
- Free fluid
Common Pitfalls to Avoid
- Relying solely on plain radiographs for diagnosis (can miss up to 40% of cases)
- Delaying CT imaging when clinical suspicion for obstruction exists
- Prolonged conservative management in high-risk patients or complete obstruction
- Missing closed-loop obstruction which requires urgent intervention
- Failure to recognize strangulation early (can lead to bowel necrosis and increased mortality)
- Administering oral contrast in suspected high-grade obstruction (risk of aspiration)
- Attributing symptoms to postoperative ileus when mechanical obstruction is present
By following this systematic approach to differentiation and management, clinicians can reduce morbidity and mortality associated with both ileus and small bowel obstruction.