CT Protocol for Suspected Perforated Viscus
Perform CT abdomen and pelvis with intravenous contrast as the first-line imaging study for suspected perforated viscus. 1, 2
Recommended CT Protocol
Primary Imaging Approach
- CT abdomen and pelvis with IV contrast is the gold standard imaging modality, with 93-96% sensitivity and 93-100% specificity for detecting perforation 1, 2
- The World Society of Emergency Surgery provides a strong recommendation (1C) for CT scan as first-line imaging in suspected perforated peptic ulcer 1, 2, 3
- CT can identify the site of perforation with 95% sensitivity and 90-94% specificity, and determine the cause with 66-87% sensitivity 2
Contrast Administration Details
- Use IV contrast for optimal visualization of perforation, abscess formation, and bowel wall enhancement 1, 2
- Oral contrast is NOT required for diagnosis of viscus perforation—a 2013 national survey found that 19% of US academic emergency departments appropriately avoid oral contrast for suspected perforation 4
- Rectal contrast is rarely indicated and not part of standard protocol 4
Coverage Area
- Full abdomen and pelvis imaging is essential, as limited field-of-view studies may miss complications extending into the upper abdomen (perihepatic or perisplenic collections) 1
Alternative Imaging When CT Unavailable
Initial Screening Options
- Chest/abdominal X-ray should be performed as initial diagnostic assessment only when CT is not promptly available (strong recommendation, 1C) 1, 2, 3
- Erect chest X-ray or left lateral decubitus abdominal films can detect free air in 30-85% of perforations, though negative X-ray does not exclude perforation 1
- Plain radiographs have 92% positive predictive value when free air is present 2
Ultrasound Considerations
- Ultrasound has limited utility for perforated viscus, with 88% sensitivity for fluid collections but very limited capacity to identify the site and cause of perforation 2
- Ultrasound may identify "dirty fluid," enhanced peritoneal stripe sign, and focal air collections with ring-down artifacts suggestive of pneumoperitoneum 5
- Consider ultrasound only in populations where radiation must be limited (children, pregnant women) or as initial screening when CT is not immediately available, but any positive or equivocal finding requires confirmatory CT 2
Additional Diagnostic Adjuncts
Water-Soluble Contrast Study
- When free air is not seen on imaging but clinical suspicion remains high, administer water-soluble contrast orally or via nasogastric tube followed by repeat imaging (weak recommendation, 2D) 1
- This approach can demonstrate active extravasation of contrast from the perforation site 1
Laboratory Studies
- Obtain routine laboratory studies and arterial blood gas analysis, though findings are non-specific (strong recommendation, 1D) 1, 3, 6
- Leukocytosis, metabolic acidosis, and elevated serum amylase are commonly associated with perforation but do not confirm diagnosis 1, 3, 6
Critical Clinical Caveats
When to Skip Imaging
- In patients with clear signs of diffuse peritonitis and hemodynamic instability, immediate surgical evaluation takes precedence over complete diagnostic workup 2
- Do not delay surgical consultation while awaiting imaging in unstable patients 2
Pitfalls to Avoid
- Free intraperitoneal air on CT is useful but not 100% specific—it can result from pneumomediastinum, bladder perforation, or previous peritoneal lavage 7
- When free air is absent, look for secondary signs: bowel wall thickening, unexplained peritoneal fluid, and peritoneal enhancement 7, 2
- Unenhanced CT may be limited in characterizing complications such as abscess formation 1