Localized type 1 autoimmune pancreatitis superimposed upon preexisting intraductal papillary mucinous neoplasms

Abstract

A 70-year-old woman was found to have 2 cystic lesions in the head of the pancreas on abdominal ultrasonography during a routine medical examination. Endoscopic ultrasonography (EUS) and magnetic resonance cholangiopancreatography showed multilocular cysts in the head of the pancreas without dilation of the main pancreatic duct. The patient was followed-up semiannually with imaging studies for suspected branch duct-type intraductal papillary mucinous neoplasm (IPMN). At 3 years after initial presentation, hypoechoic lesions were observed around each pancreatic cyst by EUS. Diffusion-weighted imaging showed high-intensity regions corresponding to these lesions. Therefore, a diagnosis of invasive carcinoma derived from IPMN could not be excluded, and subtotal stomach-preserving pancreaticoduodenectomy was performed. The macroscopic examination of the surgical specimen showed whitish solid masses in the head of the pancreas, with multilocular cysts within each mass. Microscopically, each solid mass consisted of inflammatory cells such as lymphocytes and plasma cells. Furthermore, immunochemical staining revealed immunoglobulin G4-positive cells, and many obliterating phlebitides were observed. The cysts consisted of mucus-producing epithelial cells and showed a papillary growth pattern. Based on these findings, we diagnosed multiple localized type 1 autoimmune pancreatitis occurring only in the vicinity of the branch duct-type IPMN.

Keywords: Autoimmune pancreatitis; Diffusion-weighted imaging; Endoscopic ultrasonography; Immunoglobulin G4; Intraductal papillary mucinous neoplasm.

Figure 1

Imaging studies from the initial examination. A, B: Endoscopic ultrasonography showed 2 multilocular cysts in the pancreas head; C: Magnetic resonance cholangiopancreatography showed 2 cystic lesions without dilation of the main pancreatic duct in the pancreas head.

Figure 2

Diffusion-weighted magnetic resonance imaging. A, B: In 2008, diffusion-weighted imaging showed no signal in the pancreas; C, D: In 2011, diffusion-weighted imaging showed high-intensity signals (arrow-head) corresponding to both cystic lesions in the pancreas.

Figure 3

Imaging studies at follow-up examination. A, B: Endoscopic ultrasonography revealed solid lesions in or around both cystic lesions in the pancreas head. Hyperechoic foci and strands were observed in these lesions; C: Magnetic resonance cholangiopancreatography showed a reduction in the diameter of both cystic lesions.

Figure 4

Computer tomography scan. A, B: Both cystic lesions (arrow-head) showed a lower density than the surrounding pancreatic parenchyma during the pancreatic parenchymal phase; C, D: Both cystic lesions (arrow) appeared as iso-dense in the equilibrium phases.

Figure 5

Macroscopic findings. The macroscopic examination revealed 2 whitish solid lesions with multilocular cysts (arrow, and arrow-head). Each lesion was solitary and indicated no gross continuity.

Figure 6

Microscopic findings. A: Each solid lesion presented a striform pattern with lymphoid follicles and inflammatory cells (HE, original magnification × 12.5); B: The plasma cells showed positivity for immunoglobulin G4 (HE, original magnification × 200); C: Many obliterating phlebitides were observed (HE, original magnification × 100); D: The multilocular cysts produced mucus and demonstrated a papillary pattern (HE, original magnification × 12.5).