Peribiliary glands (PGs) are located around the extrahepatic and perihilar bile ducts and are reportedly involved in the development, as well as diseases, of the hepatobiliary and pancreatic systems.1, 2
Intraductal papillary neoplasm of the bile duct (IPNB) is a newly described entity characterized by intraluminal papillary tumor(s) with mucin secretion.2 IPNB is an early neoplastic lesion of invasive cholangiocarcinoma and is proposed to be a counterpart of intraductal papillary mucinous cystic neoplasm (IPMN) of the pancreas. Though there are main duct and branch types of IPMN of the pancreas, the IPNB cases reported on, so far, seem to correspond to the main duct type, IPMN.2
Recently, there have been several reports of IPNB that might have arisen from PGs.3–6 Nakanishi et al. reported on a case in which the cystic and papillary neoplastic lesions only involved PGs.3 In another case,4 IPNB showed diverticular dilatation, and neoplastic changes involving PGs were found at the tip of the diverticular dilatation. Papillary neoplastic changes were also continuously found on the luminal surface of the neighboring bile ducts. It seems possible that the first case3 may correspond to branch-type IPMN, whereas the second case4 corresponds to the combined branch- and main-duct-type IPMN.
These cases3–6 not only suggest that cystic and papillary neoplastic changes primarily involve PGs, but also that such neoplastic cells spread to the adjacent bile duct, with the formation of IPNB showing diverticulum-like dilatation.
The relationship of PGs and the adjacent bile duct in cases of IPNB involving PGs are schematically shown in Fig. 1. In type A, neoplastic involvement is confined to PGs, and in type B, PGs are mainly involved and the adjacent bile duct(s) are also secondarily and partly involved. Type C represents extensive involvement of PGs with the simultaneously significant involvement of bile ducts. These three types can be called “branch-type IPNB,” whereas the majority of IPNB cases reported on, so far, with main duct IPMN can be called “main-duct-type IPNB.”