Yes, acute appendicitis can be visualized on CT without contrast
Non-contrast CT has high diagnostic accuracy for detecting acute appendicitis, with sensitivity of 82-94% and specificity of 75-100%, though IV contrast slightly improves sensitivity and is generally preferred when appropriate 1, 2, 3.
Diagnostic Performance of Non-Contrast CT
Non-contrast helical CT demonstrates excellent diagnostic capabilities:
- Sensitivity: 91-95% across multiple studies
- Specificity: 92-100%
- Accuracy: 93.8%
- Positive predictive value: 96.7%
- Negative predictive value: 86.8%
These numbers come from well-validated studies showing that unenhanced CT accurately diagnoses acute appendicitis without requiring contrast administration 4, 5, 3.
When Non-Contrast CT is Appropriate
The 2024 IDSA guidelines explicitly state that "CT without IV contrast also has high diagnostic accuracy in detecting acute appendicitis and may be appropriate" 1. This is particularly relevant when:
- IV access is difficult or contraindicated
- Renal function is impaired
- Contrast allergy exists
- Time is critical and contrast preparation would cause delays
- The clinical suspicion is high and appendix visualization is likely
Comparison with Contrast-Enhanced Protocols
While non-contrast CT is highly accurate, IV contrast does provide marginally better sensitivity (96% vs 91%) without significantly affecting specificity 3. The 2024 guidelines note that "IV contrast is usually appropriate whenever a CT is obtained in adults with suspected acute appendicitis" 1, but this is a preference, not an absolute requirement.
Recent systematic reviews confirm that IV-only or non-contrast protocols offer comparable diagnostic accuracy to oral contrast approaches while significantly improving workflow efficiency 2, 6.
Key Diagnostic Criteria on Non-Contrast CT
The appendix can be identified and appendicitis diagnosed based on:
- Appendiceal diameter >6 mm
- Periappendiceal inflammation (fat stranding)
- Appendiceal wall thickening
- Appendicolith presence
- Free fluid in right lower quadrant
These findings are visible without contrast enhancement 4, 5.
Clinical Pitfalls
The main limitation is that non-contrast CT has slightly lower sensitivity (91%) compared to IV-enhanced CT (96%), meaning approximately 5-9% of appendicitis cases might be missed 3. This translates to:
- At 43% prevalence: 4% probability of appendicitis after negative non-contrast CT
- Slightly higher false-negative rate compared to contrast-enhanced studies
If clinical suspicion remains high despite negative non-contrast CT, consider observation with repeat imaging or surgical consultation 1.
Bottom Line for Practice
Non-contrast CT is a legitimate and accurate imaging option for diagnosing appendicitis when contrast cannot be given or would cause unacceptable delays. However, when feasible and safe, IV contrast remains the preferred approach as it provides marginally better sensitivity while maintaining excellent specificity 1, 3.