Can diverticulitis be detected on a computed tomography (CT) scan without contrast?

Detection of Diverticulitis on CT Without Contrast

Yes, diverticulitis can be detected on CT without contrast, though contrast-enhanced CT offers superior diagnostic accuracy, particularly for detecting complications such as abscesses and perforations.

Diagnostic Accuracy of Non-Contrast CT for Diverticulitis

• Non-contrast CT is more accurate than clinical evaluation alone for diagnosing diverticulitis and can be used effectively in patients with contraindications to IV contrast material 1
• According to the American College of Radiology (ACR) Appropriateness Criteria, unenhanced CT without oral contrast receives a rating of 6 out of 9 (may be appropriate) for suspected diverticulitis, compared to 8 out of 9 (usually appropriate) for contrast-enhanced CT 1
• Recent research demonstrates that non-contrast CT is non-inferior to contrast-enhanced CT for the basic diagnosis of acute colonic diverticulitis, with an accuracy of 0.90 compared to 0.92 for contrast-enhanced CT 2

Key CT Findings Visible Without Contrast

• Even without contrast, CT can identify the hallmark findings of diverticulitis 3:
  • Colonic wall thickening (>5 mm) in the affected segment 3
  • Pericolonic fat stranding 1
  • Presence of diverticula 1
  • Extraluminal gas 1
  • Fascial thickening 1

Limitations of Non-Contrast CT

• Contrast-enhanced CT is superior for detecting complications of diverticulitis 1, 2:
  • Sensitivity for detecting abscesses is significantly lower with non-contrast CT (difference of -0.17 compared to contrast-enhanced CT) 2
  • Sensitivity for detecting perforation is also lower with non-contrast CT (difference of -0.15) 2
  • IV and oral contrast help distinguish abscesses from adjacent bowel 1
• Unenhanced CT with oral contrast is more accurate than unenhanced CT without any contrast 1
• Subtle bowel wall abnormalities may be missed without IV contrast 1

Clinical Implications and Recommendations

• When IV contrast is contraindicated (e.g., renal failure, severe contrast allergy), non-contrast CT remains a viable diagnostic option 1
• For patients with suspected complications (abscess, fistula, perforation), contrast-enhanced CT should be strongly preferred when possible 1, 2
• The ACR recommends contrast-enhanced CT as the first-line imaging modality for suspected diverticulitis due to its superior diagnostic accuracy (98%) 1, 4
• Early CT diagnosis can reduce hospital admission by more than 50% and shorten hospital length of stay 1

Alternative Imaging When Contrast Cannot Be Used

• Ultrasound may be considered as an alternative when CT with contrast is contraindicated, though it is more operator-dependent and less reliable in obese patients 1, 5
• MRI shows promise but is currently considered a second-line imaging examination with insufficient published data to support routine use 1

Practical Approach

• For patients with suspected uncomplicated diverticulitis and no contraindications to contrast: Use contrast-enhanced CT 1
• For patients with contraindications to IV contrast: Non-contrast CT is appropriate and diagnostically valuable 1, 2
• For patients with suspected complications (abscess, perforation): Make every effort to use contrast-enhanced CT if safely possible 1, 2