What is the recommended imaging study for diagnosing appendicitis?

Recommended Imaging Studies for Diagnosing Appendicitis

For non-pregnant adults with suspected acute appendicitis, abdominal CT scan is the recommended initial imaging modality due to its high diagnostic accuracy. 1, 2

Population-Specific Recommendations

Adults

• First-line imaging: Abdominal CT with IV contrast
  • High sensitivity (95%) and specificity (94%) 3
  • CT without IV contrast also has high diagnostic accuracy and may be appropriate when IV contrast is contraindicated 1, 2
  • If CT is negative but clinical suspicion remains high, consider observation with supportive care (with/without antibiotics) or surgical intervention 1

Children and Adolescents

• First-line imaging: Abdominal ultrasound 1, 2
  • Avoids radiation exposure
  • Operator-dependent and may yield equivocal results
  • If initial US is equivocal/non-diagnostic and clinical suspicion persists:
    • Proceed to MRI or CT as subsequent imaging 1, 2
    • CT involves radiation exposure and may require IV contrast or sedation
    • MRI may require sedation for young children

Pregnant Patients

• First-line imaging: Abdominal ultrasound 1, 2
  • Avoids radiation exposure to the fetus
  • If initial US is equivocal:
    • Proceed to MRI as subsequent imaging 1, 2
    • MRI is reasonable as initial imaging if readily available 1

Advantages and Limitations of Each Modality

CT Scan

• Advantages:
  • Highest diagnostic accuracy (sensitivity 95%, specificity 94%) 3
  • Less operator-dependent than ultrasound
  • Can identify alternative diagnoses
• Limitations:
  • Radiation exposure
  • Potential contrast-related complications

Ultrasound

• Advantages:
  • No radiation exposure
  • Readily available in most settings
  • Excellent for children and pregnant patients
• Limitations:
  • Operator-dependent
  • Limited visualization in obese patients or retrocecal appendix 2, 4
  • Lower sensitivity (33-35%) compared to CT (78-80%) 5

MRI

• Advantages:
  • No radiation exposure
  • High sensitivity and specificity
  • Excellent for pregnant patients and as second-line for children
• Limitations:
  • Limited availability in some settings
  • May require sedation in young children
  • Longer acquisition time than CT

Common Pitfalls and Caveats

1. Retrocecal appendicitis: Often missed on ultrasound, requiring CT for diagnosis 4
2. Equivocal findings: When initial imaging is inconclusive but clinical suspicion remains high, consider:
   • Additional imaging rather than repeated use of the same modality
   • Surgical consultation if high clinical suspicion persists despite negative imaging 1
3. Contrast enhancement: CT with IV contrast provides higher sensitivity than unenhanced CT, though both have similar specificity 3
4. Radiation concerns: Balance diagnostic accuracy with radiation exposure, especially in young patients and pregnant women

The choice of imaging should be guided by patient characteristics, local expertise, and resource availability, but CT remains the gold standard for adults due to its superior diagnostic performance 2, 6.