Is ultrasound (US) beneficial for diagnosing diverticulitis?

Ultrasound for Diagnosing Diverticulitis: Benefits and Limitations

While ultrasound (US) can be beneficial for diagnosing diverticulitis with high sensitivity (>90%), CT remains the preferred initial imaging modality due to superior diagnostic accuracy, especially for detecting complications and alternative diagnoses. 1

Diagnostic Accuracy of Ultrasound for Diverticulitis

• Ultrasound demonstrates sensitivity of >90% and positive predictive value of >90% in meta-analyses and prospective studies for diagnosing diverticulitis, though accuracy is modestly less than CT 1
• Acute diverticulitis can be diagnosed by US using three key criteria:
  1. Short-segment colonic wall thickening (>5 mm)
  2. Inflamed diverticulum in the thickened area (hypoechoic and surrounded by hyperechoic fat)
  3. Noncompressible hyperechoic pericolic tissue 1
• Recent studies show high accuracy for ruling out or diagnosing diverticulitis using point-of-care ultrasound protocols, with sensitivity of 95% and negative predictive value of 93% 2

Limitations of Ultrasound for Diverticulitis

• US is less accurate than CT for diagnosing complicated diverticulitis, with sensitivity as low as 55% for detecting complications 2
• US accuracy is particularly diminished in obese patients and for distal sigmoid diverticulitis 1
• US requires a higher level of operator expertise than CT, with estimates suggesting a minimum of 500 examinations required for competency 1
• US is less likely to identify alternative diagnoses compared to CT 1

Current Guideline Recommendations

• The 2024 Infectious Diseases Society of America (IDSA) guideline suggests CT as the initial diagnostic modality for non-pregnant adults with suspected acute diverticulitis (conditional recommendation, very low certainty of evidence) 1
• If CT is unavailable or contraindicated, the IDSA suggests obtaining an ultrasound or MRI as the alternative diagnostic modality 1
• The 2023 American College of Radiology (ACR) Appropriateness Criteria acknowledges that while US is the initial imaging test for suspected diverticulitis in some European countries, it is not widely used in the United States, partly due to a larger obese population 1

Potential Benefits of Ultrasound

• Non-invasive with no radiation exposure 1
• If used as initial imaging at the bedside (point-of-care), US may reduce the number of CT scans performed without negative effect on patient care 1
• Faster time to diagnosis compared to standard care (97 ± 102 vs. 330 ± 319 minutes) 3
• May be particularly useful in early, uncomplicated diverticulitis 4

Clinical Implementation Strategy

• Consider US as first-line imaging in:
  • Patients with contraindications to CT (renal insufficiency, contrast allergy)
  • Pregnant patients (where US or MRI are preferred over CT) 1
  • Young patients with typical presentation to minimize radiation exposure 1
• Proceed to CT if:
  • US is inconclusive or negative despite high clinical suspicion 1, 3
  • Complicated diverticulitis is suspected (abscess, perforation, fistula) 2
  • Patient is obese or has distal sigmoid involvement 1

Pitfalls and Caveats

• Relying solely on US may miss complicated diverticulitis; studies show that approximately half of complicated cases may be missed or misclassified as simple diverticulitis 2
• Operator dependence is a significant limitation; diagnostic accuracy varies with sonographer experience 1, 4
• US has lower specificity than CT and is less likely to identify alternative diagnoses that may mimic diverticulitis 1
• Transvaginal US is not useful for diagnosing diverticulitis but remains important for evaluating gynecologic causes of pelvic pain 1

In conclusion, while ultrasound offers benefits as a rapid, radiation-free initial imaging option with good sensitivity for uncomplicated diverticulitis, CT remains the gold standard due to superior accuracy, especially for detecting complications and alternative diagnoses.