In a patient with suspected complicated diverticulitis, is non‑contrast magnetic resonance imaging (MRI) superior to non‑contrast computed tomography (CT) for diagnosis?

Plain MRI vs Plain CT in Complicated Diverticulitis

Non-contrast CT is superior to non-contrast MRI for diagnosing complicated diverticulitis and should be the preferred imaging modality when contrast is contraindicated. 1, 2

Diagnostic Performance: Non-Contrast CT

Non-contrast CT demonstrates excellent diagnostic accuracy for diverticulitis:

• Sensitivity of 92-99% and specificity of 97-100% for detecting diverticulitis, even without intravenous contrast 1
• More accurate than clinical evaluation alone and can effectively diagnose diverticulitis in patients with contraindications to IV contrast 2
• Successfully identifies key diagnostic features including pericolonic fat stranding, presence of diverticula, extraluminal gas, and fascial thickening 2

Diagnostic Performance: Non-Contrast MRI

Non-contrast MRI has more limited evidence and lower specificity:

• Sensitivity of 94% (95% CI: 82-99%) but specificity of only 88% (95% CI: 47-100%) 1
• The evidence comparing CT with MRI is of low certainty due to indirect comparisons and small sample sizes 1
• MRI shows promise but remains a second-line examination with insufficient published data to support routine use 2, 3

Critical Limitation for Complicated Disease

The major disadvantage of non-contrast imaging for complicated diverticulitis:

• Contrast-enhanced CT is superior for detecting complications such as abscesses and perforations, with IV and oral contrast helping to distinguish abscesses from adjacent bowel 2
• Subtle bowel wall abnormalities may be missed without IV contrast 2
• Unenhanced CT with oral contrast is more accurate than unenhanced CT without any contrast 2

Practical Algorithm

When evaluating suspected complicated diverticulitis:

1. First choice: Contrast-enhanced CT (IV + oral contrast) - this is the gold standard 1, 2

2. If IV contrast is contraindicated: Non-contrast CT remains viable and diagnostically valuable, though less sensitive for complications 2

3. If CT is unavailable or contraindicated: Consider ultrasound or MRI as alternatives, though both have significant limitations 1

4. For pregnant patients: Ultrasound or MRI can be considered, with no clear preference between the two 1

Common Pitfalls

Avoid these critical errors:

• Do not rely on non-contrast imaging when complications are suspected - every effort should be made to use contrast-enhanced CT if safely possible 2, 4
• Missing a complicated diverticulitis can have important clinical implications; if diverticulitis is suspected, obtain a CT scan to confirm diagnosis and exclude complications 5
• Non-contrast CT receives a rating of only 6 out of 9 (may be appropriate) compared to 8 out of 9 (usually appropriate) for contrast-enhanced CT according to ACR Appropriateness Criteria 2

Guideline Recommendations

The 2024 IDSA guidelines clearly state:

• CT is suggested as the initial imaging modality for non-pregnant adults with suspected acute diverticulitis (conditional recommendation) 1
• If CT is unavailable or contraindicated, ultrasound or MRI can be considered as alternatives 1
• The panel is unable to recommend one imaging modality versus the other when comparing ultrasound and MRI 1