Multilocular Cyst of Type 1 Autoimmune Pancreatitis Masquerading as Cancerization of Intraductal Papillary Mucinous Neoplasm

Abstract

A small proportion of intraductal papillary mucinous neoplasms (IPMNs) are accompanied by type 1 autoimmune pancreatitis (AIP); however their clinical courses and image characteristics have not been fully reported. A 65-year-old woman was referred to our hospital for the examination of a pancreatic head cyst that had shown exacerbation for two years. Several images demonstrated a multilocular cyst with a symmetrically thickened, enhanced, cyst wall. Cancerization of IPMN was suspected, and pancreatoduodenectomy was performed. The resected specimens showed a multilocular cyst with solid areas. The solid areas demonstrated pathological findings that corresponded with type 1 AIP. Papillary epithelia suggestive of IPMN was recognized in some parts of the cystic wall.

Keywords: IgG4; autoimmune pancreatitis; diagnosis; intraductal papillary mucinous neoplasms.

Figure 1.

Serial computed tomography showing a multilocular cyst at the pancreas head in the initial examination (A), and an enhanced and thickened cystic wall two years later (B).

Figure 2.

Endoscopic retrograde cholangiopancreatography showing the dilated main pancreatic duct (MPD), communicating with the pancreas head branch, and a filling defect floating inside the MPD.

Figure 3.

Magnetic resonance imaging. A T1-weighted image showing a low-intensity signal around the multilocular cyst (A). A T2-weighted image showing multiple locules depicted with high-intensity signals (B). A diffusion-weighted image showing reduced diffusing capacity at the cystic wall (C).

Figure 4.

Endoscopic ultrasound showing multiple locules with circular, symmetric wall thickening, like a lotus root.

Figure 5.

Pathology. The cut surface of the resected pancreas showing a multilocular cyst with a homogeneous whitish thickened wall (arrowheads) and a solid area (arrows) (A), confirmed by loupe finding [Hematoxylin and Eosin (H&E) staining] (B). Papillary epithelial projections secreting mucin, like intraductal papillary mucinous neoplasm (IPMN) (H&E staining, ×40) (C), diffusely positive for MUC5AC (MUC5AC, ×40) (D). Storiform fibrosis (H&E staining, ×100) (E) and obliterating phlebitis (H&E staining, ×100) (F) recognized in the solid area around the multilocular cyst. Abundant IgG4-positive lymphoplasmacytic infiltration was positively detected not only in the solid area (IgG4, ×100) (G), but also in the papillary epithelia covering the cyst (IgG4, ×200) (H).