Multifocal autoimmune pancreatitis:A retrospective study in a single tertiary center of 26 patients with a 20-year literature review

BACKGROUND Multifocal-type autoimmune pancreatitis(AIP),sometimes forming multiple pancreatic masses,is frequently misdiagnosed as pancreatic malignancy in routine clinical practice.It is critical to know the imaging features of multifocaltype AIP to prevent misdiagnosis and unnecessary surgery.To the best of our knowledge,there have been no studies evaluating the value of diffusionweighted imaging(DWI),axial fat-suppressed T1 weighted image(T1WI),and dynamic contrast enhanced-computed tomography(DCE-CT)in detecting the lesions of multifocal-type AIP.AIM To clarify the exact prevalence and radiological findings of multifocal AIP in our cohorts and compare the sensitivity of DWI,axial fat-suppressed T1WI,and DCECT for detecting AIP lesions.We also compared radiological features between multifocal AIP and pancreatic ductal adenocarcinoma with several key imaging landmarks.METHODS Twenty-six patients with proven multifocal AIP were retrospectively included.Two blinded independent radiologists rated their confidence level in detecting the lesions on a 5-point scale and assessed the diagnostic performance of DWI,axial fat-suppressed T1WI,and DCE-CT.CT and magnetic resonance imaging of multifocal AIP were systematically reviewed for typical imaging findings and compared with the key imaging features of pancreatic ductal adenocarcinoma.RESULTS Among 118 patients with AIP,26(22.0%)had multiple lesions(56 lesions).Ulcerative colitis was associated with multifocal AIP in 7.7%(2/26)of patients,and Crohn’s disease was present in 15.3%(4/26)of patients.In multifocal AIP,multiple lesions,delayed homogeneous enhancement,multifocal strictures of the main pancreatic duct,capsule-like rim,lower apparent diffusion coefficient values,and elevated serum Ig4 level were observed significantly more frequently than pancreatic ductal adenocarcinoma,whereas the presence of capsule-like rim in multifocal-type AIP was lower in frequency than total AIP.Of these lesions of multifocal AIP,DWI detected 89.3%(50/56)and 82.1%(46/56)by the senior and junior radiologist,respectively.CONCLUSION Multifocal AIP is not as rare as previously thought and was seen in 22.0%of our patients.The diagnostic performance of DWI for detecting multifocal AIP was best followed by axial fat-suppressed T1WI and DCE-CT.