What are the typical findings on a CT scan of the abdomen in a patient with diverticulitis?

CT Findings in Diverticulitis

CT scan is the most useful examination for patients with suspected diverticulitis, showing characteristic findings including pericolonic fat stranding, bowel wall thickening, and diverticula with a diagnostic accuracy of 98%. 1

Key CT Findings in Diverticulitis

• Colonic wall thickening (>5 mm) in the affected segment, most commonly in the sigmoid colon 1
• Pericolonic fat stranding (inflammation in the pericolic fat) - present in 98% of cases 2
• Presence of diverticula - visible in 84% of cases 2
• Inflamed diverticulum - appears as a thickened diverticulum at the epicenter of inflammatory changes 1
• Pericolic abscess - seen as rim-enhancing fluid collection adjacent to the affected bowel segment in approximately 35% of cases 1, 2
• Free fluid - may be present in the abdomen or pelvis 1
• Extraluminal gas - small-volume pericolic air (<5 cm from affected segment) in uncomplicated cases or distant air (>5 cm) in complicated cases 1
• Fascial thickening in the affected area 1
• Arrowhead sign - arrowhead-shaped configuration of contrast material at the orifice of the inflamed diverticulum 1

Classification Based on CT Findings

CT findings help classify diverticulitis into:

1. Uncomplicated diverticulitis:

   • Inflammation limited to colonic wall and surrounding tissue 3
   • Colonic wall thickening with increased perivisceral fat density 4

2. Complicated diverticulitis:

   • Stage 1A: Microperforation without abscess and/or peritoneum involvement 4
   • Stage 1B: Abscess ≤4 cm in diameter 4
   • Stage 2A: Abscess >4 cm in diameter 4
   • Stage 2B: Distant air >5 cm from the pathological loop 4
   • Stage 3: Diffuse fluid in at least two distant abdominal quadrants without distant free air 4
   • Stage 4: Diffuse fluid and distant free air 4

Clinical Implications of CT Findings

• CT can predict which patients are likely to experience recurrent diverticulitis - colonic wall thickness <9 mm has a 19% recurrence risk 1
• CT findings help in risk-stratification for operative versus non-operative treatment 1
• CT assists in determining inpatient versus outpatient triage - early CT can reduce hospital admission by more than 50% 1
• CT helps identify complications requiring intervention:
  • Abscesses ≥3 cm typically require catheter drainage 1
  • Free perforation and peritonitis require surgical intervention 1
  • Fistulas and strictures can be identified 1

Technical Considerations

• IV contrast improves detection of subtle bowel wall abnormalities and complications like abscesses 1
• For most patients, IV or intracavitary contrast is not necessary for diagnosis 1
• Unenhanced CT is more accurate than clinical evaluation alone and can be used in patients with contraindications to IV contrast 1
• Radiation dose-reduced CT (50%-90% less than standard dose) maintains similar sensitivity and specificity 1

Pitfalls and Caveats

• CT may not differentiate diverticulitis from colon cancer in some cases, necessitating follow-up colonoscopy after resolution of acute symptoms 3
• Small diverticula may be missed if bowel is not adequately distended 1
• Distal sigmoid diverticulitis may be more difficult to visualize due to its pelvic location 1
• CT findings must be correlated with clinical presentation, as incidental diverticulosis is common in older adults 5
• Atypical presentations or diagnostic ambiguity warrant additional investigation 3