Computed tomography characteristics of acute pancreatitis based on different etiologies at different onset times: a retrospective cross-sectional study.

Background: The clinical characteristics and imaging findings of acute pancreatitis (AP) are different across the various etiologies, the results are conflicting, and their time from symptom onset to imaging varies. The imaging findings of different etiologies at different onset times are unclear. This study aimed to investigate the computed tomography (CT) characteristics of AP based on different etiologies at different onset times. Methods: Patients who underwent plain and contrast-enhanced computed tomography (CECT) for the first attack of AP in 3 hospitals (Affiliated Hospital of North Sichuan Medical College, Chinese People's Liberation Army Western Theater General Hospital, and Suining Central Hospital) from 2015 to 2019 were recruited. According to the different etiologies of AP, the patients were divided into 5 subgroups: biliary AP (n=591), alcoholic AP (n=267), hypertriglyceridemic AP (n=258), mixed causes subgroups (n=199), and "other/idiopathic" AP (n=545). According to the time from onset to CT examination (e.g., 1-3, 4-7, 8-14, 15-28, and >28 days), the onset time was divided into 5 respective phases (I-V). The CT characteristics and clinical and laboratory features were retrospectively reviewed and compared among the different etiology subgroups and onset time. Results: The positive rate of CT findings in AP diagnosis based on CECT was 96.7% (1,860/1,924). Necrotizing pancreatitis (NP) occurred in 33.2% (617/1,860) of AP patients with positive CECT findings. Among patients with NP, local complications and severe AP of the modified CT severity index (MCTSI) increased over time in those with biliary AP from 17.1%, 25.2%, and 20.0% in Phase I to 42.9%, 44.0%, and 39.7% in Phase IV [all P<0.05, 95% confidence interval (CI): 0.15 to 0.52, 0.28 to 0.63, and 0.18 to 0.82, respectively]. In contrast, NP, local complications and severe AP of MCTSI in those with hypertriglyceridemic AP decreased over time from 24.3%, 22.5%, and 22.7% in Phase I to 1.3%, 1.2%, and 1.9% in Phase V (all P<0.05, 95% CI: 3.20 to 181.74, 3.31 to 175.74, and 2.00 to 120.78, respectively). Conclusions: The proportion of NP was 33.2% of positive CECT findings. There may be differences in the CT and clinical manifestations of the different etiologies, and those differences may be related to the onset time.