What imaging study should be ordered if ileus is suspected?

Imaging for Suspected Ileus

For suspected ileus, CT abdomen and pelvis with IV contrast is the recommended first-line imaging study as it provides the highest diagnostic accuracy and can differentiate between mechanical obstruction and paralytic ileus with 100% sensitivity and specificity. 1

Diagnostic Approach for Suspected Ileus

First-Line Imaging

• CT Abdomen and Pelvis with IV contrast
  • Provides superior diagnostic accuracy compared to plain radiographs
  • Can differentiate between mechanical obstruction and paralytic ileus
  • Identifies the site and cause of obstruction
  • Detects complications such as ischemia and strangulation 2
  • No oral contrast is required for suspected high-grade obstruction as the fluid-filled bowel provides adequate intrinsic contrast

Alternative Imaging Options

Plain Abdominal Radiographs

• Traditional starting point but with inconsistent diagnostic accuracy:
  • Sensitivity ranges from 30-90% for small bowel obstruction 2
  • May be misleading in 20-40% of patients 2
  • Cannot reliably differentiate between ileus and mechanical obstruction
  • May prolong evaluation time if used as first-line imaging

Ultrasound

• Limited utility for ileus in adults due to:
  • Operator dependency
  • Difficulty visualizing gas-filled bowel
  • Limited assessment of the entire gastrointestinal tract 2
• May be considered in specific populations:
  • Pediatric patients 2, 3
  • Pregnant patients 2
  • When radiation exposure is a significant concern

MRI

• Not recommended for routine evaluation of suspected ileus 2
• Consider in specific situations:
  • Patients with multiple prior CT examinations
  • Patients expected to need multiple future imaging examinations
  • Pregnant patients (non-contrast sequences) 2

Clinical Considerations

When to Choose CT Without Oral Contrast

• In acutely ill patients unable to tolerate oral contrast
• When high-grade obstruction is suspected
• When there is concern for aspiration risk
• When rapid diagnosis is needed

When to Consider Plain Radiographs First

• In resource-limited settings
• As a quick screening tool in critically ill patients before proceeding to CT
• When CT is not immediately available

Common Pitfalls to Avoid

• Relying solely on plain radiographs for definitive diagnosis
• Failing to differentiate between mechanical obstruction and paralytic ileus
• Delaying CT when clinical suspicion for obstruction is high
• Using oral contrast in suspected high-grade obstruction (risk of vomiting and aspiration)

Special Populations

• Pediatric patients: Consider ultrasound as initial imaging 2
• Pregnant patients: Consider ultrasound or non-contrast MRI 2
• Patients with renal insufficiency: Consider non-contrast CT or MRI

CT abdomen and pelvis with IV contrast remains the gold standard for evaluating suspected ileus, offering the highest diagnostic accuracy and providing crucial information about etiology and complications that will guide appropriate management decisions.