What type of CT scan is used to diagnose a suspected Small Bowel Obstruction (SBO)?

CT Scan for Suspected Small Bowel Obstruction

For suspected high-grade SBO, obtain a CT abdomen and pelvis with IV contrast but WITHOUT oral contrast—this achieves >90% diagnostic accuracy and is the definitive imaging modality of choice. 1

High-Grade or Acute SBO Protocol

CT with IV contrast only is the optimal approach for the following reasons:

• Diagnostic accuracy exceeds 90% for detecting obstruction, identifying the transition point, and determining the cause 1, 2
• IV contrast is essential to assess bowel perfusion and detect ischemia, which carries up to 25% mortality if missed 1, 2
• Oral contrast should NOT be used in suspected high-grade SBO because:
  • The nonopacified fluid in dilated bowel provides adequate intrinsic contrast 1
  • It delays diagnosis and increases patient discomfort 1
  • It increases aspiration risk in patients who may vomit 1
  • It obscures abnormal bowel wall enhancement patterns that indicate ischemia 1

Critical CT Findings to Assess

The CT must evaluate for life-threatening complications that require immediate surgery 1:

• Bowel ischemia signs: Abnormal bowel wall enhancement (decreased or increased), intramural hyperdensity, bowel wall thickening, mesenteric edema, ascites, pneumatosis, or mesenteric venous gas 1
• Closed-loop obstruction or volvulus: These lead directly to ischemia if untreated 1
• Transition point location: Multiplanar reconstructions increase accuracy in localizing this, which guides surgical planning 1

Important Caveat About Ischemia Detection

While CT signs of ischemia are highly specific when present, CT is unfortunately not sensitive for ischemia—prospective sensitivity is only 14.8% based on initial radiology reports 1. Even with retrospective expert review, sensitivity reaches only 30-52% 1. Therefore, clinical correlation is essential, and when ischemia is suspected clinically, do not rely solely on CT to rule it out 1.

Low-Grade or Intermittent SBO Protocol

For suspected intermittent or low-grade SBO with indolent presentation, standard CT abdomen/pelvis has reduced sensitivity (only 48-50%) 1. In these cases:

• CT enterography or CT enteroclysis are preferred, offering improved sensitivity and specificity over standard CT 1
• Oral contrast may be purposefully given in low-grade cases to challenge bowel distensibility and identify subtle transition points 1
• CT enteroclysis (nasoduodenal tube with controlled contrast infusion) is most accurate but has limited availability and patient acceptance in the United States 1
• CT enterography (oral contrast ingestion protocol without intubation) provides greater bowel distention than standard CT and has better patient acceptance 1

Follow-Up Imaging Strategy

If a transition point is identified but oral contrast does not pass beyond it, re-imaging at 24 hours can demonstrate contrast passage, indicating incomplete/partial obstruction 1

Technical Specifications

• Multidetector CT with multiplanar reconstruction is significantly more effective than older single-slice CT for evaluating SBO 1
• Dual-energy CT may improve detection of bowel ischemia using iodine maps and virtual monoenergetic images 1
• Noncontrast CT has comparable accuracy for diagnosing high-grade SBO itself, but determination of ischemia is significantly reduced 1

Alternative Imaging Modalities

• Plain radiographs have limited value with only 60-70% sensitivity/specificity and may prolong evaluation 2, 3
• MRI has excellent accuracy (positive likelihood ratio 6.77) but is less practical in acute settings 4
• Ultrasound shows surprisingly high accuracy (positive likelihood ratio 14.1 for formal scans, 9.55 for bedside scans) but is operator-dependent and not widely used for this indication in the United States 1, 4