Non-Contrast CT for Bowel Perforation
CT scan with IV contrast is the first-line diagnostic imaging modality for suspected bowel perforation, with 93-96% sensitivity and 93-100% specificity; non-contrast CT should be avoided as it has limited ability to characterize perforation and associated complications. 1, 2
Why IV Contrast is Essential
- Unenhanced CT has significant limitations in characterizing complicated bowel pathology, including perforation and abscess formation, making it inadequate for this clinical scenario 1
- CT with IV contrast achieves 95% sensitivity and 90-94% specificity for identifying the exact site of perforation, which is critical for surgical planning 2
- The World Society of Emergency Surgery provides a strong recommendation (1C) that CT scan should be the primary imaging modality for suspected gastrointestinal perforation 1, 2
Diagnostic Algorithm
When CT is immediately available:
- Proceed directly to CT abdomen and pelvis with IV contrast as the definitive diagnostic test 1, 2
- This provides comprehensive assessment of perforation site, underlying cause, and complications such as abscess or bowel obstruction 1, 3
When CT is not immediately available:
- Obtain chest/abdominal X-ray as initial screening, which has 92% positive predictive value for detecting free air 1, 2
- If X-ray is negative but clinical suspicion remains high, CT with IV contrast must still be performed, as 15-70% of perforations show no free air on plain films 1
- Ultrasound may serve as a screening tool in radiation-sensitive populations (children, pregnant women), but any positive or equivocal finding requires CT confirmation 2
Key CT Findings to Identify
Direct signs of perforation (diagnostic):
- Extraluminal gas or air-fluid levels 4, 5
- Bowel wall discontinuity 6, 4
- Contrast extravasation (when oral or IV contrast is used) 5, 7
Indirect signs (supportive):
- Localized bowel wall thickening with pericolic fat stranding 6, 4
- Abscess formation or feculent collections adjacent to bowel 6
- Free intraperitoneal fluid without solid organ injury 5
Critical Pitfalls to Avoid
- Never rely on non-contrast CT alone for suspected perforation, as it cannot adequately characterize the extent of complications or guide surgical approach 1
- Use bone window settings on CT to increase conspicuity of free air, which can be easily missed on standard soft tissue windows 4
- Be aware that absence of free air does not exclude perforation—4% of proven perforations show no extraluminal gas on CT 7
- Do not mistake pneumothorax, pneumomediastinum, or venous air for pneumoperitoneum 4
When Contrast is Contraindicated
- If IV contrast cannot be given due to severe renal dysfunction or allergy, consider adding water-soluble oral or nasogastric contrast to improve diagnostic yield 1
- In hemodynamically unstable patients with clear peritonitis, proceed directly to surgical exploration without delaying for complete imaging workup 2