Size matters: Computed tomographic measurements of the appendix in emergency department scans

Radiologists use a size cutoff in appendiceal diameter to assist surgeons in diagnosing appendicitis, however, no consensus exists as to the size of a normal adult appendix. We aim to evaluate radial appendiceal diameter on CT in adult patients both with and without appendicitis.

Retrospective review of adults who underwent abdominal CT was performed. Variables collected include: demographics, BMI, WBC count at presentation, radial diameter of appendix (mm), presence of fat stranding, fecalith, and free fluid.

During the study period, 3099 patients underwent CT. The appendix was visualized on 74% of scans. Mean appendiceal diameter was 6.6 mm (±1.7). The appendix was larger in patients with appendicitis (6.6 vs. 11.4; p < 0.0001). Overall appendectomy incidence was 3.2%. Sensitivity and specificity of CT in diagnosing appendicitis in this cohort of patients were 90% and 94%. NPV was 99.5%.

While appendiceal diameter was larger in patients with appendicitis, >20% of patients without appendicitis had an appendiceal diameter >7 mm. Diameter alone should not be relied upon to diagnose appendicitis.