What are the indications for a computed tomography (CT) scan in adults over 40 with a history of diverticulosis?

Indications for CT in Diverticulosis

CT abdomen and pelvis with IV contrast is indicated when a patient with known diverticulosis develops acute symptoms suggesting diverticulitis, including left lower quadrant pain, fever, or systemic signs of infection. 1

Primary Indications for CT Imaging

Suspected Acute Diverticulitis

• CT is the preferred initial imaging modality for any adult with clinically suspected acute diverticulitis, achieving sensitivity of 95-100% and specificity of 97-100% for diagnosis 1
• CT should be obtained when patients with known diverticulosis present with:
  • Acute or severe left lower quadrant pain with or without fever 1
  • Chronic, intermittent, or low-grade left lower quadrant pain 1
  • Systemic symptoms suggesting complications (persistent fever, chills, increasing leukocytosis) 2, 3

High-Risk Clinical Scenarios Requiring CT

• No prior imaging-confirmed diagnosis of diverticulitis - clinical diagnosis alone is correct in only 40-65% of cases 2
• Severe presentation suggesting complications such as abscess, perforation, or peritonitis 1, 2
• Failure to improve with therapy after 48-72 hours of treatment 2
• Immunocompromised patients (chemotherapy, high-dose steroids, transplant recipients) who are at increased risk for complicated disease and treatment failure 1, 2, 3
• Symptom duration >5 days before presentation 2
• Signs of perforation, bleeding, obstruction, abscess, or fistula on clinical examination 2
• Obesity - where ultrasound performance is significantly limited 1

Critical Diagnostic and Prognostic Value

Disease Severity Assessment

• CT grading determines treatment strategy: moderate diverticulitis (localized wall thickening >5mm, pericolonic fat stranding) has 4% risk of requiring surgery during acute episode, while severe diverticulitis (abscess, extraluminal air, free fluid) has 26% risk 4, 5
• CT identifies complications that alter management in 65% of elderly patients and changes surgical decisions in 48% 6
• Specific CT findings predict outcomes: longer segments of involved colon, retroperitoneal abscess, and extraluminal air are associated with recurrence, medical treatment failure, and need for surgery 1

Ruling Out Alternative Diagnoses

• CT can identify other causes of left lower quadrant pain including ovarian pathology, leaking aortic/iliac aneurysm, ureterolithiasis, appendicitis, and colon cancer 1
• CT findings suggesting colon cancer rather than diverticulitis include pericolonic lymphadenopathy >1cm in short axis 6, 2

Alternative Imaging Considerations

When Ultrasound May Be Considered First

• Ultrasound can be used as initial imaging only when performed by an expert operator (minimum 500 examinations required for competency) with CT follow-up for inconclusive cases 1
• Ultrasound has sensitivity of 90% and specificity of 90% but is significantly limited in obese patients and for detecting free gas and deeply located abscesses 1

When CT Should Be Avoided

• Pregnant patients - MRI or ultrasound should be considered as alternatives, though MRI has sensitivity of 94% and specificity of 88% 1
• Women of childbearing age - only after gynecologic etiologies have been clinically or sonographically excluded 1

Critical Pitfalls to Avoid

• Do not rely on inflammatory markers alone - up to 39% of patients with complicated diverticulitis have CRP <175 mg/L, and in very acute disease CRP may not have risen yet (6-8 hour delay from onset) 1, 6
• Do not assume elderly patients will present typically - only 50% have lower quadrant pain, only 17% have fever, and 43% lack leukocytosis 6, 7
• Do not delay CT in high-risk patients - mortality increases significantly with age (1.6% in <65 years vs 17.8% in >80 years) 7
• Small-volume pericolic air (<5cm from affected segment) can be managed medically, but spilled feces generally requires surgery - CT distinguishes these critical findings 1