Appendix Size and Diagnostic Criteria

Diameter Measurements

Appendices <6 mm in diameter are nearly always normal on both ultrasound and CT imaging, according to the American College of Radiology 1, 2
Appendices >8 mm are nearly always abnormal, with optimal CT cutoff values ranging from 8.2 mm (sensitivity 88.8%, specificity 93.4%) to 11 mm (sensitivity 62.7%) depending on the study, as reported by the American College of Radiology 1
The 6 mm cutoff yields high sensitivity (97.5%) but poor specificity (59.6%), meaning it captures most appendicitis cases but generates many false positives, according to the American College of Radiology 1, 3
Diameter alone should not be relied upon to diagnose appendicitis in the borderline range; secondary findings become critical, as recommended by the American College of Radiology 1

Wall thickness >3 mm is significantly associated with perforation (OR 3.2, P=0.02), according to the American College of Radiology 1, 4

Compressed diameter (after accounting for compressible luminal contents) performs better than maximal outer diameter, with optimal cutoff of 6.6 mm yielding 93.8% sensitivity and 94.9% specificity, as reported by the American College of Radiology 1, 3

Periappendiceal fat stranding is associated with an increased risk of perforation (OR 5.63, P<0.001), according to the American College of Radiology 1
Appendicoliths are associated with an increased risk of perforation (OR 2.47-2.67), as reported by the American College of Radiology 1, 4, 5
Intraluminal gas is associated with an increased risk of perforation (OR 2.64; sensitivity 36.9%, specificity 81.9%), according to the American College of Radiology 1, 4
Focal wall defects are associated with an increased risk of perforation (OR 23.40; specificity 98.8%), as reported by the American College of Radiology 1