Recommended Initial Imaging for Suspected Complicated Diverticulitis
Obtain an abdominal and pelvic CT scan with intravenous contrast as the initial imaging test for any non-pregnant adult with suspected complicated diverticulitis. 1
Primary Recommendation
CT abdomen and pelvis with IV contrast is the gold standard initial imaging modality, demonstrating exceptional diagnostic accuracy with sensitivity of 92-99% and specificity of 97-100% for acute diverticulitis. 1, 2 This recommendation comes from the 2024 Infectious Diseases Society of America (IDSA) guidelines, which specifically suggest CT as first-line imaging despite acknowledging very low certainty of evidence. 1
Why CT with IV Contrast is Superior
IV contrast is usually appropriate because it helps characterize subtle bowel wall abnormalities and detect complications such as abscesses, though CT without IV contrast remains more accurate than clinical evaluation alone if contrast is contraindicated. 1
CT excels at identifying complications that determine whether you need surgery, interventional drainage, or medical management alone—specifically detecting perforation, abscess formation (particularly those ≥3 cm requiring drainage), fistulae, and peritonitis. 1, 3
CT prevents unnecessary hospital admissions by accurately diagnosing uncomplicated diverticulitis that can be managed outpatient, reducing admissions by more than 50% and shortening hospital length of stay. 1
CT identifies alternative diagnoses with high accuracy, which is critical since misdiagnosis based on clinical assessment alone occurs in 34-68% of cases. 1
Alternative Imaging When CT is Unavailable or Contraindicated
If CT is unavailable or contraindicated, obtain ultrasound (US) or MRI as the initial diagnostic modality. 1
Ultrasound Considerations
US demonstrates sensitivity >90% and positive predictive value >90% in meta-analyses, diagnosing diverticulitis using three key criteria: short-segment colonic wall thickening, inflamed diverticulum, and noncompressible hyperechoic pericolic tissue. 4
Major limitations of US include: significantly diminished accuracy in obese patients and for distal sigmoid diverticulitis, requirement for high operator expertise (minimum 500 examinations for competency), and reduced ability to identify alternative diagnoses compared to CT. 4
US is most useful in early, uncomplicated diverticulitis in non-obese patients, and the American College of Radiology acknowledges it is not widely used in the United States partly due to a larger obese population. 4, 5
MRI Considerations
- MRI yields sensitivity of 94% and specificity of 88%, but evidence quality is low due to limited studies and small sample sizes. 1, 2
Special Population: Pregnant Patients
For pregnant adults with suspected diverticulitis, use US or MRI to avoid radiation exposure, though the IDSA guidelines acknowledge a knowledge gap and cannot recommend one modality over the other. 1, 2
Common Pitfalls and Caveats
Do not rely on clinical assessment alone in elderly patients or those on corticosteroids, as they may have limited physical examination findings even with severe diverticulitis. 6
Imaging is essential regardless of laboratory values in elderly patients, despite the 39.4% prevalence of chronic kidney disease in those over 60 years—the diagnostic benefit generally justifies the risk of contrast-induced acute kidney injury. 2, 7
If using US as initial imaging and results are inconclusive or negative despite high clinical suspicion, proceed immediately to CT rather than delaying diagnosis. 4
Minimize contrast volume (<350 mL or <4 mL/kg) and use low-osmolar or iso-osmolar contrast media to reduce nephropathy risk, with isotonic saline hydration at 1 mL/kg/hour for 12 hours before and after contrast if GFR <40-45 mL/min/1.73 m². 7
Prognostic Value of CT Findings
Colonic wall thickness on CT has prognostic significance: wall thickness <9 mm predicts only 19% recurrence risk, which can inform counseling about surveillance versus operative management. 1, 2