Best Imaging for Diverticulitis
Contrast-enhanced abdominal and pelvic CT is the best initial imaging modality for diagnosing diverticulitis in non-pregnant adults, with sensitivity of 92-99% and specificity of 97-100%. 1, 2
Primary Recommendation: CT Imaging
The Infectious Diseases Society of America (2024) and the American College of Radiology (2023) both recommend CT as the first-line imaging modality for suspected acute diverticulitis. 1 This recommendation is based on CT's superior diagnostic accuracy compared to all other modalities. 1
Key CT Protocol Details
Intravenous contrast is usually appropriate and helps characterize subtle bowel wall abnormalities and detect complications like abscesses, though CT without IV contrast remains more accurate than clinical evaluation alone and can be used when contrast is contraindicated. 1
Radiation dose-reduced CT (50-90% less than standard dose) maintains similar sensitivity and specificity to standard-dose CT for acute diverticulitis. 1
Clinical Impact of CT
Early CT diagnosis in the emergency department can reduce hospital admissions by more than 50% and shorten hospital length of stay, since most diverticulitis is uncomplicated and manageable with outpatient antibiotics. 1
CT predicts recurrence risk: colonic wall thickness <9 mm correlates with only 19% recurrence risk, helping guide decisions between surveillance and operative management. 1
CT identifies complications including abscesses, perforation, fistulas, and strictures that alter management from conservative to interventional or surgical approaches. 1, 3
Alternative Imaging When CT Unavailable or Contraindicated
Ultrasound
If CT is unavailable or contraindicated, ultrasound or MRI should be obtained as the initial diagnostic modality. 1
Ultrasound demonstrates sensitivity >90% and positive predictive value >90% in meta-analyses, though accuracy is modestly less than CT. 4 European experts recommend US as first-line imaging, but it remains underutilized in the United States, partly due to higher obesity rates. 1, 4
US diagnostic criteria for acute diverticulitis: 1, 4
- Short-segment colonic wall thickening (>5 mm)
- Inflamed diverticulum in the thickened area (hypoechoic, surrounded by hyperechoic fat)
- Noncompressible hyperechoic pericolic tissue
Critical US limitations: 4
- Accuracy particularly diminished in obese patients and for distal sigmoid diverticulitis
- Requires minimum of 500 examinations for operator competency
- Less likely to identify alternative diagnoses compared to CT
- May miss up to 80% of complicated diverticulitis cases 1
MRI
MRI yields sensitivity of 94% and specificity of 88%, but diagnostic accuracy is likely less than CT and insufficiently studied with limited data from small, biased studies. 1 MRI is less sensitive for extraluminal gas than CT and more affected by motion artifacts, particularly problematic in severely ill patients. 1
Special Population: Pregnant Patients
In pregnant adults with suspected acute diverticulitis, US or MRI can be considered for imaging, though the IDSA guideline panel cannot recommend one modality over the other due to insufficient evidence. 1 This represents a knowledge gap where radiation avoidance must be balanced against diagnostic accuracy.
Common Pitfalls to Avoid
Do not rely on plain radiography as the initial imaging test—it is not useful for diagnosing diverticulitis in the general population, though it may identify large-volume extraluminal air or bowel obstruction. 1
Do not perform colonoscopy during acute flare-up—it should be considered six weeks after symptom resolution in patients with complicated diverticulitis who lack recent high-quality colonoscopy. 5
Do not assume US alone is sufficient for complicated diverticulitis—proceed to CT if US is inconclusive, negative despite high clinical suspicion, or if complicated disease is suspected. 4
Do not skip imaging in favor of clinical diagnosis alone—unenhanced CT is more accurate than clinical evaluation alone, and imaging confirms diagnosis, assesses severity, and guides appropriate management. 1