What is the recommended imaging protocol for appendicitis workup, specifically regarding the use of computed tomography (CT) with or without contrast?

CT Imaging Protocol for Appendicitis Workup

For adults with suspected acute appendicitis, CT with intravenous contrast is the recommended first-line imaging modality, while CT without contrast is also acceptable with only slightly lower diagnostic accuracy. 1

Adult Imaging Protocol

First-Line Imaging:

• CT abdomen and pelvis with IV contrast is the preferred initial imaging study for adults with suspected appendicitis
  • Sensitivity: 96%
  • Specificity: 93-94%
  • Does not require oral contrast for optimal diagnostic accuracy 1

Alternative Options:

• CT without IV contrast is an acceptable alternative when IV contrast is contraindicated
  • Slightly lower sensitivity (90-91%) but still high specificity (94%) 1, 2
  • Particularly useful in patients with contrast allergies or renal insufficiency

Contrast Considerations:

• IV contrast improves visualization of the appendiceal wall and surrounding inflammation
• Oral contrast is generally unnecessary and may delay diagnosis without improving accuracy 1, 3
• Rectal contrast shows high sensitivity (97%) and specificity (95%) but causes patient discomfort and carries risk of perforation (0.04%) 1, 2, 4

Special Populations

Children:

• Ultrasound should be the initial imaging modality to avoid radiation exposure 1
• If ultrasound is equivocal or non-diagnostic:
  • MRI is preferred as the second-line imaging if available
  • CT with IV contrast is appropriate if MRI is unavailable or impractical 1

Pregnant Women:

• Ultrasound should be the initial imaging modality 1
• If ultrasound is equivocal:
  • MRI without contrast is the preferred second-line imaging 1
  • CT should be avoided due to radiation exposure to the fetus

Clinical Pearls and Pitfalls

• Pitfall: Waiting for oral contrast can delay diagnosis and potentially increase perforation risk
• Pitfall: Non-contrast CT may yield inconclusive results in up to 25% of cases, potentially requiring repeat scanning with contrast 1
• Pearl: CT without IV contrast still has high diagnostic accuracy (sensitivity 90%, specificity 94%) and can be used when IV contrast is contraindicated 2
• Pearl: Focused CT of the lower abdomen/pelvis may be sufficient for diagnosis while reducing radiation exposure 1

Diagnostic Accuracy of CT for Appendicitis

CT Protocol	Sensitivity	Specificity	Notes
IV contrast	96%	93-94%	Preferred standard approach
No contrast	90-91%	94%	Acceptable alternative
Rectal contrast	97%	95%	High accuracy but patient discomfort
IV + oral contrast	96%	94%	No added benefit over IV alone

In summary, for adult patients with suspected appendicitis, CT with IV contrast represents the optimal balance of diagnostic accuracy, efficiency, and patient comfort. When IV contrast is contraindicated, non-contrast CT remains a highly accurate alternative.