Autoimmune pancreatitis: disease evolution, staging, response assessment, and CT features that predict response to corticosteroid therapy.

PURPOSE: To evaluate the evolution of morphologic features of autoimmune pancreatitis (AIP) at computed tomography (CT) and to identify imaging features that can predict AIP response to corticosteroid therapy (CST).

MATERIALS AND METHODS: This HIPAA-compliant retrospective study had institutional review board approval. From among a cohort of 63 patients with AIP, 15 patients (12 men, three women; mean age, 64.7 years; age range, 30-84 years) who underwent sequential CT examinations before treatment were included to assess the evolution of disease by reviewing pancreatic, peripancreatic, and ductal changes. Of these patients, 13 received CST and underwent posttreatment CT; these CT studies were evaluated to determine if there were imaging features that could predict response to CST.

RESULTS: The disease evolved from changes of diffuse (14 of 15 patients) or focal (one of 15 patients) parenchymal swelling, peripancreatic stranding (10 of 15 patients), "halo" (nine of 15 patients), pancreatic duct changes (15 of 15 patients), and distal common bile duct narrowing (12 of 15 patients) to either resolution or development of ductal strictures and/or focal masslike swelling. In 13 patients treated with CST, favorable response to treatment was seen in those with diffuse pancreatic and peripancreatic changes. Suboptimal response was seen in patients with ductal stricture formation (two of 13 patients) and in those in whom focal masslike swellings persisted after resolution of diffuse changes (seven of 13 patients).

CONCLUSION: CT features like diffuse swelling and halo respond favorably to CST and likely reflect an early inflammatory phase, whereas features like ductal strictures and focal masslike swelling are predictive of a suboptimal response and symbolize a late stage with predominance of fibrosis.