What is the diagnostic test of choice for suspected acute sigmoid diverticulitis?

Diagnostic Test of Choice for Suspected Acute Sigmoid Diverticulitis

Computed tomography (CT) scan of the abdomen and pelvis is the diagnostic test of choice for suspected acute sigmoid diverticulitis. 1, 2

Evidence Supporting CT as First-Line Imaging

CT is the preferred initial imaging modality for suspected acute sigmoid diverticulitis for several key reasons:

• Superior diagnostic accuracy: CT demonstrates sensitivity of 94-99% and specificity of 96-99% for diverticulitis 2
• Reproducibility: CT provides consistent results with reported overall accuracy of 98% 1
• Complication detection: CT excels at identifying complications such as abscess, fistula, obstruction, and perforation 1
• Alternative diagnosis identification: CT can reveal other causes of left lower quadrant pain that may mimic diverticulitis 1
• Treatment stratification: CT findings help determine appropriate management (outpatient vs. inpatient, medical vs. surgical) 1

CT Protocol Considerations

• IV contrast enhancement: Recommended to improve characterization and detection of subtle bowel wall abnormalities and complications 1
• Oral/rectal contrast: Not routinely required for diagnosis of uncomplicated diverticulitis 2
• Low-dose techniques: Can achieve 75-90% radiation dose reduction compared to standard protocols while maintaining diagnostic accuracy 1

Alternative Imaging Options

Ultrasound

• Good alternative when CT is contraindicated
• Sensitivity and specificity around 90% 2
• Diagnostic criteria include:
  1. Short-segment colonic wall thickening (>5 mm)
  2. Inflamed diverticulum in thickened area
  3. Noncompressible hyperechoic pericolic tissue 1, 2
• Limitations:
  • Less reliable in obese patients
  • Less accurate for distal sigmoid diverticulitis
  • Highly operator-dependent (requires ~500 examinations for competency) 1, 2
  • Lower specificity than CT 1

MRI

• Alternative with sensitivity 94%, specificity 88% 2
• Less sensitive than CT for detecting extraluminal gas 2
• May be preferred in young patients or those requiring repeated imaging to reduce radiation exposure 2
• Limited by longer acquisition times and patient motion artifacts 1

Contrast Enema Studies (Barium/Gastrografin)

• Historically used but now largely replaced by cross-sectional imaging
• Contraindicated in acute setting due to potential complications 3
• Lower diagnostic accuracy compared to CT 4

Why Not Other Options?

• Barium enema: Contraindicated in acute diverticulitis due to risk of barium peritonitis if perforation is present 1
• Gastrografin enema: Less accurate than CT and invasive; risk of exacerbating inflammation 3
• Abdominal ultrasound: While useful, has lower accuracy than CT, especially in obese patients and distal sigmoid disease 1
• Colonoscopy: Contraindicated in acute diverticulitis due to risk of perforation; appropriate only after resolution of acute episode 3

Clinical Pitfalls to Avoid

• Do not rely solely on clinical assessment for diagnosis, as misdiagnosis rates range from 34-68% 2
• Do not exclude diverticulitis based on normal inflammatory markers alone 2
• Be aware that elderly patients often present atypically (only 50% with lower quadrant pain, 17% with fever) 2
• Consider a step-up approach (ultrasound followed by CT if inconclusive) in young patients to reduce radiation exposure 2

In conclusion, CT abdomen and pelvis with IV contrast is the diagnostic test of choice for suspected acute sigmoid diverticulitis due to its superior diagnostic accuracy, ability to detect complications, and role in guiding appropriate management.