Which abdominal x-ray view is best for diagnosing an ileus?

Abdominal X-Ray Views for Diagnosing Ileus

For diagnosing ileus, obtain both supine and upright (or left lateral decubitus) abdominal radiographs, as the upright view is essential for detecting air-fluid levels and distinguishing mechanical obstruction from paralytic ileus. 1

Recommended Radiographic Views

Standard Two-View Approach

• Supine radiograph: Provides baseline assessment of bowel gas pattern and bowel loop dilatation 1
• Upright or left lateral decubitus radiograph: Critical for detecting air-fluid levels and pneumoperitoneum 1
  • The upright view specifically allows visualization of differential air-fluid level heights within the same bowel loop, which is highly predictive of mechanical obstruction versus ileus 2
  • If the patient cannot stand, a left lateral decubitus view serves as an alternative for pneumoperitoneum assessment 1

Key Radiographic Findings

Distinguishing Features on Upright Films

• Air-fluid levels of differential height in the same small-bowel loop are highly significant (p ≤ 0.0003) for mechanical obstruction rather than paralytic ileus 2
• Mean air-fluid level width ≥25 mm on upright radiographs is the second most predictive finding for high-grade obstruction 2
• When both critical findings are present, mechanical obstruction is likely; when both are absent, ileus or low-grade obstruction is more probable 2

General Radiographic Findings

• Bowel loop dilatation is detected in 88.89% of cases on plain films 3
• Air-fluid levels are observed in approximately 77.78% of obstructive cases 3
• Pneumobilia may be visible in specific conditions like gallstone ileus (37.04% sensitivity on plain films) 3

Important Limitations and Caveats

When Plain Films Are Insufficient

• Radiographs have limited sensitivity (49%) for detecting bowel obstruction and poor visualization of bowel pathology 1
• Plain films cannot reliably distinguish between paralytic ileus and mechanical obstruction in many cases, particularly in the postoperative setting where clinical and radiographic findings combined show only 19% sensitivity 4
• CT is superior for definitive diagnosis, with 100% sensitivity and specificity for distinguishing postoperative ileus from complete mechanical obstruction 4

Optimal Timing Consideration

• Early imaging is crucial: The earlier ultrasound or advanced imaging is performed, the more diagnostic information is obtained, as it may take up to 6 hours to develop classical radiographic findings 5
• In the "empty abdomen" (minimal fluid and gas), ultrasound can detect early peristaltic disorders and wall abnormalities before plain film findings become apparent 5

When to Proceed Beyond Plain Films

• If plain films show bowel dilatation with air-fluid levels but clinical picture remains unclear, proceed directly to CT with IV contrast for definitive diagnosis 1, 4
• CT should be the method of choice in postoperative patients or when distinguishing mechanical obstruction from ileus is clinically critical 4
• Ultrasound can provide additional real-time assessment of peristalsis and bowel wall characteristics, particularly useful when plain films are non-diagnostic 5