Interpretation of computed tomography does not correlate with laboratory or pathologic findings in surgically confirmed acute appendicitis

Abstract

Background: Computed tomography (CT) is used increasingly to diagnose acute appendicitis, despite variable technique and interpretation. We hypothesized that CT interpretation would not reflect actual clinical-pathologic findings in all demographic patient groups.

Methods: A prospective university hospital database of 625 consecutive patients (1995-1999), all of whom were operated on for appendicitis (261, or 41.8%, within 24 hours of discretionary CT), was reviewed. CT and pathology data were obtained from final, written reports. CT criteria included free fluid or air, appendiceal visualization, mesenteric fat stranding, and blurred pericecal fat. Appendix pathology included acute, gangrenous, and perforated organs. Statistics were performed with the Fisher exact test (coordinate data) and univariate analysis of variance (continuous data); multivariate analysis of variance for independent effects on dependent variable (positive CT or pathology; P <.05).

Results: The mean age was 35 +/- 1 years with 46.6% being female patients. CT was done more often in women and after 1997 (both P <.05). The sensitivity and specificity of CT were 96.1% and 16.1%, respectively. The positive predictive value (PPV) and accuracy rate (A) were 90%, and 88%, respectively. After CT, the incidence of finding a normal appendix was lower (19.3% vs 12.3%, P <.05), especially if the white blood cell count (WBC) was normal (< or = 11K/microL, 6.1% vs 23.2%, P <.001). If the WBC was < or = 11K/microL with positive CT, PPV/A was 73. 7%/71.3%, whereas with WBC > 11K/microL and positive CT, PPV/A was 99.4%/93.3%. Multivariate analysis of variance showed that none of the individual variables used by the radiologist to determine a positive CT scan correlated with outcome determined by surgical pathology. A healthy appendix was predicted by a CT interpreted as negative and younger age (both P <.05), and especially by lower WBC (P <.0001), but not by gender or surgeon.

Conclusions: Although the negative appendectomy rate was decreased by CT, there was no correlation between CT findings and pathologically proved disease. Other factors such as more precise patient selection by clinical criteria may also be improving outcome. A positive CT scan in a patient with a normal WBC should be interpreted with caution.