PMC9513040_01
The MRI features of irAP and its improvement after treatment. The MRI at diagnosis revealed a slightly swollen pancreas with multiple nodular (A, arrow) and patchy abnormal signals with decreased intensity on T1WI sequences (A) and increased intensity on DWI (B, arrow) located in the pancreatic head and tail. MRCP showed segmental stenosis of the MPD in the pancreatic head (C, arrow). After 1 month of prednisolone treatment, the swelling reduced and the abnormal signals decreased on T1W1 (D) and DWI (E) sequences. The MPD stenosis also resolved (F, arrow). irAP, immune-related acute pancreatitis; MRI, magnetic resonance imaging; T1W1, T1-weighted image; DWI, diffusion-weighted imaging; MPD, main pancreatic duct; MRCP, magnetic resonance cholangiopancreatography.
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The pancreatic head showed only slight hyper-enhancement, and no significant abnormal enhancement was observed in the delayed phase ( Figures 1A-C ). Magnetic resonance cholangiopancreatography (MRCP) showed a decrease in the nodular and patchy abnormal signals, especially in the pancreatic body and tail ( Figures 1D, E ). The segmental stenosis of the MPD resolved with the consequent resolution of the distal MPD dilation ( Figure 1F ).
The EUS and histopathological features. EUS revealed a slightly swollen pancreas with heterogeneous echoic signals and scattered hyperechoic strips in the parenchyma (A, B). The pancreatic duct was regular without dilatation, and the pancreatic tail was slightly enlarged without a mass lesion (C, D). Pancreatic biopsy shows retention of the lobular architecture with focal atrophy of acini infiltrated with neutrophils and lymphocytes (E, HE staining,x150; F, HE staining, x400). The lymphocytes were predominately T cells (G, CD3 IHC), although scattered B cells (H, CD20 IHC) were also present. CD8+ T cells (I, CD8 IHC) tended to dominate compared with CD4+ counterparts (J, CD4 IHC). EUS, endoscopic ultrasound; IHC, immunohistochemistry; HE, hematoxylin-eosin.
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On EUS, the pancreas was slightly swollen, and the echoic signals were slightly heterogeneous with scattered, striped hyperechoic areas in the parenchyma without obvious masses; the pancreatic tail was slightly enlarged ( Figures 2A-D ). Histopathological examination of the needle core biopsy showed retention of the normal lobular architecture with focal acinar atrophy associated with a neutrophil and lymphocyte predominant infiltrate ( Figures 2E, F ) but no fibrosis. T cells (CD8+ > CD4+), although scattered B cells were seen ( Figures 2G-J ).