Abstract： Objective:To summarize the MRI features of intrapancreatic accessory spleen (IPAS) and G1 grade pancreatic neuroendocrine neoplasms (PNENs), and clarify the radiological features for differential diagnosis.Methods:The data of 11 patients with IPAS confirmed by surgical pathology or 99mTc thermal denatured red blood cell imaging and 9 patients with G1 grade PNENs confirmed by surgical pathology in the tail of pancreas from January 2013 to December 2019 admitted in First Affiliated Hospital of Navy Medical University were retrospectively analyzed. MRI features of IPAS group and PNENs group, including shape, size, whether it protruded beyond the contour of the pancreas, cystic degeneration, plain scan of T 2WI, DWI signal, multistage enhancement mode, false capsule, etc. were studied and compared. Results:There was significantly statistical difference between the two groups in the terms of contour protrusion, T 2WI and DWI signals, multistage enhancement, and pseudomembrane (all P< 0.05). Protruded lesion was more common in the PNENs group (9/9 cases) than in the IPAS group (3/11). The T 2WI and DWI signals of lesions in the PNENs group were slightly higher than those in the IPAS group, and the proportion of high T 2WI and DWI signal lesions in the PNENs group was 6/9 cases and 4/9 cases, respectively, while the proportion of high T 2WI and DWI signal lesions in the IPAS group was 0/11 cases. Multistage enhancement of lesions in the PNENs group was more likely to be consistent (6/9), while lesions in the IPAS group were more inconsistent (10/11). In the PNENs group, all lesions showed false envelope after enhancement (9/9), while in the IPAS group, no false envelope was observed after enhancement (0/11). Conclusions:The presence of protruded lesions, the characteristics of T 2WI and DWI signals, the mode of multiphase enhancement and the false envelope were essential signs for differentiating IPAS and G1 grade PNENs.