Diagnosis of acute appendicitis with sliding slab ray-sum interpretation of low-dose unenhanced CT and standard-dose i.v. contrast-enhanced CT scans.

OBJECTIVE

The purpose of this study was to compare low-dose unenhanced CT with standard-dose i.v. contrast-enhanced CT in the diagnosis of appendicitis.

MATERIALS AND METHODS

Two hundred seven adults with suspected appendicitis underwent CT with mean effective doses of both 4.2 and 8.0 mSv. Two radiologists retrospectively reviewed thin-section images by sliding a 5-mm-thick ray-sum slab. They rated the likelihood of appendicitis and appendiceal visualization on 5- and 3-point scales, respectively, and proposed alternative diagnoses. Likelihood > or = 3 was considered a positive diagnosis. Receiver operating characteristics analysis, the McNemar test, and the Wilcoxon's signed-rank test were used.

RESULTS

Seventy-eight patients had appendicitis. The values of the area under the receiver operating characteristics curve were 0.98 for the low-dose unenhanced acquisition and 0.97 for the standard-dose contrast-enhanced acquisition for reader 1 (95% CI for the difference, -0.02 to 0.03) and 0.99 and 0.98 (-0.02 to 0.02) for reader 2. Sensitivity was 98.7% for low-dose unenhanced CT and 100% for standard-dose contrast-enhanced CT for reader 1 (p = 1.00) and 100% for both techniques for reader 2. Specificity was 95.3% and 93.0% (p = 0.25) and 96.9% and 96.9%. The interpretation was indeterminate (score 3) in 0.5% and 1.4% of cases for reader 1 (p = 0.63) and 0.5% and 0% for reader 2 (p = 1.00). A normal appendix was not visualized in 5.4% and 3.9% of cases by reader 1 (p = 0.63) and 3.9% and 2.3% of cases by reader 2 (p = 0.50). None of the patients whose appendix was not visualized had appendicitis. Diagnostic confidence, visualization score for a normal appendix, and correct alternative diagnosis tended to be compromised with use of low-dose unenhanced CT, showing a significant difference for a reader's confidence in the diagnosis of appendicitis (p = 0.004). The two techniques were comparable in the diagnosis of appendiceal perforation.

CONCLUSION

Low-dose unenhanced CT is potentially useful in the diagnosis of appendicitis.