Does a computed tomography (CT) abdomen for appendicitis require contrast?

CT Abdomen for Appendicitis: Contrast Requirements

IV contrast is recommended for CT abdomen when evaluating suspected appendicitis, as it improves diagnostic accuracy compared to non-contrast CT, though non-contrast CT still maintains good diagnostic performance. 1

Diagnostic Performance of Different CT Techniques

• CT with IV contrast demonstrates superior sensitivity (96%) compared to unenhanced CT (90-91%) for diagnosing appendicitis 2
• CT with IV contrast helps highlight inflammation in the appendiceal wall and surrounding periappendiceal tissues, improving visualization of the inflammatory process 2
• Specificity remains comparable between contrast-enhanced CT (93%) and unenhanced CT (94%) 2
• The American College of Radiology recommends CT with IV contrast as the initial imaging modality for non-pregnant adults with suspected appendicitis 1

Oral Contrast Considerations

• Oral contrast is generally not necessary and may delay diagnosis without significantly improving accuracy 1
• A systematic review of 23 studies showed that oral contrast does not improve the accuracy of CT for diagnosing appendicitis 2
• Weighted sensitivities and specificities from this review: non-contrast CT (93% and 98%), CT with oral and IV contrast (93% and 93%), and CT with rectal contrast (97% and 97%) 2
• Oral contrast requires additional time to administer, transit the bowel, and may be difficult to tolerate for patients with abdominal pain and vomiting 2

Special Populations

• In children, ultrasound is recommended as the initial imaging modality, with CT abdomen with IV contrast as a second-line test if ultrasound is equivocal/non-diagnostic 1
• In pregnant patients, ultrasound should be the initial imaging modality, with MRI without IV contrast preferred over CT if ultrasound is equivocal 1

Clinical Implications

• The improvement in diagnostic accuracy achieved by adding IV contrast is significant, with sensitivity increasing from 90% to 96% 2
• IV contrast helps identify conditions other than acute appendicitis (e.g., diverticulitis, inflammatory bowel disease, cancer) 2
• IV contrast is particularly helpful in thin patients with low body mass index who lack sufficient mesenteric fat to demonstrate periappendiceal fat stranding 2

Potential Drawbacks of Contrast

• IV contrast may lead to allergic reactions and renal failure in susceptible patients 2
• Contrast adds to the cost of the examination 2
• When IV contrast is contraindicated, non-contrast CT still maintains good diagnostic performance with sensitivity of 90-91% and specificity of 94-98% 2, 3

Practical Approach

• For most adult patients with suspected appendicitis, CT with IV contrast without oral contrast is the preferred approach 2, 1
• If IV contrast is contraindicated, non-contrast CT is still a reasonable alternative with good diagnostic performance 2
• The appendix is easier to detect on contrast-enhanced CT than non-contrast CT images 4
• Modern multi-detector CT technology has improved diagnostic accuracy, potentially reducing but not eliminating the advantage of contrast 2

In conclusion, while non-contrast CT maintains good diagnostic performance, the evidence supports the use of IV contrast for CT abdomen when evaluating suspected appendicitis due to its superior sensitivity and ability to better characterize appendiceal inflammation and identify alternative diagnoses.