In an adult with suspected acute diverticulitis, what type of computed tomography (CT) scan should be performed?

CT Abdomen/Pelvis with Intravenous Contrast

For adults with suspected acute diverticulitis, obtain a CT abdomen and pelvis with intravenous (IV) contrast as the initial diagnostic imaging study. 1, 2

Imaging Protocol Specifications

IV contrast is the critical component that should be used whenever CT is obtained for suspected diverticulitis, as it significantly improves detection of:

• Subtle bowel wall abnormalities and mural enhancement from inflammation 1, 2
• Complications including abscess formation, perforation, and fistula formation 2
• Accurate staging to distinguish uncomplicated from complicated disease 2

The diagnostic performance of CT with IV contrast is excellent:

• Sensitivity: 92-99% 1
• Specificity: 97-100% 1

When IV Contrast Cannot Be Used

CT without IV contrast may be appropriate in select circumstances (e.g., severe renal impairment, contrast allergy), though sensitivity for detecting complications drops significantly. 1 One study found similar diagnostic performance with low-dose unenhanced CT compared to contrast-enhanced CT, but this is not the standard recommendation. 1

Alternative Imaging Modalities

If CT is unavailable or contraindicated, use this algorithm:

Second-line options (in order of preference):

• Ultrasound: Sensitivity 61-100%, specificity 99-100% 1, 2
  • Limited by operator dependence, patient obesity, and abdominal tenderness 1
• MRI: Sensitivity 94%, specificity 88% 1
  • Less readily available, more costly, longer acquisition time 1

Special Population: Pregnancy

For pregnant patients with suspected diverticulitis, use ultrasound or MRI as the initial imaging modality to avoid radiation exposure. 1, 2 The guidelines cannot recommend one over the other due to insufficient evidence. 1

Critical Pitfalls to Avoid

• Do not rely on clinical diagnosis alone: Misdiagnosis rates range from 34-68% without imaging, and only 25% of patients present with the classic triad of left lower quadrant pain, fever, and leukocytosis. 2
• Do not delay imaging in elderly patients: Clinical presentation is atypical in 50% of elderly patients, and CT influences treatment plans in 65% of cases. 2
• Do not skip IV contrast without good reason: Sensitivity for detecting complications (abscess, perforation) is significantly lower without IV contrast enhancement. 2, 3

Clinical Impact

Early CT imaging provides substantial benefits:

• Reduces hospital admissions by >50% 2
• Shortens length of stay 2
• Allows accurate triage between outpatient and inpatient management 2
• Identifies complications requiring intervention (abscesses ≥3-4 cm need percutaneous drainage) 2