What are the criteria for ordering a computed tomography (CT) abdomen with intravenous (IV) contrast to rule out appendicitis?

Criteria for CT Abdomen with IV Contrast to Rule Out Appendicitis

In non-pregnant adults with suspected acute appendicitis, CT abdomen with IV contrast is the recommended initial imaging modality due to its high sensitivity and specificity for diagnosing appendicitis. 1

Adult Patients

Clinical Criteria for Ordering CT Abdomen with IV Contrast:

• Right lower quadrant pain with fever and leukocytosis 1
• Atypical presentation of right lower quadrant pain with fever and leukocytosis 1
• Persistent clinical suspicion of appendicitis despite equivocal findings on physical examination 1

Technical Considerations:

• IV contrast is usually appropriate for CT evaluation of suspected appendicitis 1
• CT without IV contrast also has high diagnostic accuracy (sensitivity ~91%, specificity ~98%) but may have limitations in characterizing complicated appendicitis 1, 2
• CT with IV contrast offers superior sensitivity (96%) compared to unenhanced CT (91%) 3
• Oral contrast is generally not necessary and may delay diagnosis without significantly improving accuracy 1, 4
• Standard coverage of abdomen and pelvis is typically performed, though focused CT from L2/L3 to pubic symphysis may be sufficient 1

Special Populations

Children:

• Ultrasound is recommended as the initial imaging modality in children with suspected appendicitis 1
• If ultrasound is equivocal/non-diagnostic and clinical suspicion persists, CT abdomen with IV contrast is appropriate as a second-line imaging test 1
• Reduced-dose CT protocols should be considered to minimize radiation exposure while maintaining diagnostic accuracy 1

Pregnant Patients:

• Ultrasound is recommended as the initial imaging modality 1
• If ultrasound is equivocal, MRI without IV contrast is preferred over CT to avoid radiation exposure 1

Diagnostic Performance

• CT with IV contrast demonstrates sensitivity of 96-100% and specificity of 93-95% for diagnosing appendicitis 1, 3
• IV contrast administration makes appendix identification easier and improves sensitivity compared to non-contrast CT 5
• CT helps identify alternative diagnoses that may mimic appendicitis, such as diverticulitis, inflammatory bowel disease, gynecologic disorders, and urologic conditions 6

Common Pitfalls and Caveats

• If CT is negative but clinical suspicion remains high, consider observation with supportive care, with or without antibiotics; surgical intervention may still be warranted in cases of high clinical suspicion despite negative imaging 1
• CT with both IV and oral contrast approximately doubles radiation exposure without improving diagnostic performance compared to CT with IV contrast alone 1
• CT with IV contrast alone allows for faster ED disposition (approximately 1.5 hours faster) compared to CT with both IV and oral contrast 4
• Unenhanced CT has limitations in characterizing complicated appendicitis (e.g., perforation and abscess formation) and may have lower sensitivity for alternative diagnoses 1