Computed Tomography Findings Associated with Treatment Failure after Antibiotic Therapy for Acute Appendicitis

OBJECTIVE: To identify the CT findings associated with treatment failure after antibiotic therapy for acute appendicitis. MATERIALS AND METHODS: Altogether, 198 patients who received antibiotic therapy for appendicitis were identified by searching the hospital's surgery database. Selection criteria for antibiotic therapy were uncomplicated appendicitis with an appendiceal diameter equal to or less than 11 mm. The 86 patients included in the study were divided into a treatment success group and a treatment failure group. Treatment failure was defined as a resistance to antibiotic therapy or recurrent appendicitis during a 1-year follow-up period. Two radiologists independently evaluated the following CT findings: appendix–location, involved extent, maximal diameter, thickness, wall enhancement, focal wall defect, periappendiceal fat infiltration, and so on. For the quantitative analysis, two readers independently measured the CT values at the least attenuated wall of the appendix by drawing a round region of interest on the enhanced CT (HU(post)) and non-enhanced CT (HU(pre)). The degree of appendiceal wall enhancement (HU(sub)) was calculated as the subtracted value between HU(post) and HU(pre). A logistic regression analysis was used to identify the CT findings associated with treatment failure. RESULTS: Sixty-four of 86 (74.4%) patients were successfully treated with antibiotic therapy, with treatment failure occurring in the remaining 22 (25.5%). The treatment failure group showed a higher frequency of hypoenhancement of the appendiceal wall than the success group (31.8% vs. 7.8%; p = 0.005). Upon quantitative analysis, both HU(post) (46.7 ± 21.3 HU vs. 58.9 ± 22.0 HU; p = 0.027) and HU(sub) (26.9 ± 17.3 HU vs. 35.4 ± 16.6 HU; p = 0.042) values were significantly lower in the treatment failure group than in the success group. CONCLUSION: Hypoenhancement of the appendiceal wall was significantly associated with treatment failure after antibiotic therapy for acute appendicitis.