Diverticulitis Imaging
Primary Recommendation
For non-pregnant adults with suspected acute diverticulitis, obtain an abdominal CT scan with intravenous contrast as the initial imaging modality. 1
Diagnostic Performance
CT demonstrates exceptional diagnostic accuracy for acute diverticulitis:
The 2024 Infectious Diseases Society of America (IDSA) guideline explicitly recommends CT as the first-line imaging test, though this is a conditional recommendation based on very low certainty of evidence. 1
CT Protocol Specifications
Intravenous contrast is usually appropriate and should be administered whenever possible to improve characterization and detection of:
- Subtle bowel wall abnormalities 1
- Complications including abscess formation 1, 2
- Bowel wall enhancement patterns 2
- Perforation 2
The American College of Radiology rates CT with IV contrast as 8 out of 9 (usually appropriate) compared to only 6 out of 9 for non-contrast CT. 2
When Non-Contrast CT is Acceptable
CT without IV contrast may be appropriate in patients with contraindications to contrast, as unenhanced CT remains more accurate than clinical evaluation alone. 1
Radiation Dose Reduction
Request low-dose CT protocols when available, as radiation dose-reduced techniques (50-90% less than standard dose) maintain similar sensitivity and specificity for acute diverticulitis without compromising diagnostic accuracy. 1, 2
Alternative Imaging Modalities
When CT is Unavailable or Contraindicated
If CT cannot be performed, obtain ultrasound (US) or MRI as the initial diagnostic modality. 1
Ultrasound Considerations
US demonstrates reasonable diagnostic performance:
- Sensitivity and positive predictive value: >90% 3
- Diagnostic criteria include: short-segment colonic wall thickening (>5 mm), inflamed diverticulum in thickened area, and noncompressible hyperechoic pericolic tissue 1, 3
Critical limitations of ultrasound:
- Accuracy significantly diminished in obese patients and for distal sigmoid diverticulitis 1, 3
- Requires high operator expertise (minimum 500 examinations for competency) 3
- Lower specificity than CT and less likely to identify alternative diagnoses 1, 3
- Operator-dependent with variable diagnostic accuracy based on sonographer experience 3
While European guidelines recommend US as first-line imaging, it remains underutilized in the United States partly due to a larger obese population. 1, 3
MRI Performance
MRI yields a sensitivity of 94% (95% CI: 82-99%) and specificity of 88% (95% CI: 47-100%). 1
MRI is not appropriate for acute evaluation due to:
- Limited availability in emergency settings 2
- Difficulty detecting extraluminal air 2
- Motion artifacts in acutely ill patients 2
- Insufficient published data to support routine use 1
Special Population: Pregnancy
In pregnant adults with suspected acute diverticulitis, either US or MRI can be considered for imaging. The IDSA guideline panel is unable to recommend one modality over the other due to a knowledge gap. 1
Consider US as first-line in pregnant patients to minimize radiation exposure, proceeding to MRI if US is inconclusive. 3
Imaging Modalities to Avoid
Plain Radiography
Do not rely on abdominal X-rays as they are extremely limited, detecting only large amounts of free air while missing small perforations and providing no information about bowel wall or mesenteric vessels. 1, 2
Contrast Enema
Avoid contrast enema studies as they:
- Only show secondary effects of inflammation 2
- Miss extraluminal abnormalities like abscesses 2
- Increase perforation risk in acute diverticulitis 2
- Lack sensitivity compared to CT 4
Clinical Algorithm
Non-pregnant adult with suspected diverticulitis → CT abdomen/pelvis with IV contrast 1, 2
If CT contraindicated or unavailable → US or MRI 1
If US performed and inconclusive or negative despite high clinical suspicion → Proceed to CT 3
Pregnant patient → US first-line, consider MRI if inconclusive 1, 3
Patient with contrast allergy → Non-contrast CT (still superior to clinical evaluation alone) 1
Common Pitfalls
Relying solely on ultrasound may miss complicated diverticulitis, particularly in obese patients or when evaluating the distal sigmoid colon. 3
Ordering MRI for acute evaluation causes unnecessary delays due to limited availability and longer acquisition times. 2
Using plain radiography as the primary diagnostic test will miss the majority of clinically significant findings. 1, 2