Diagnosis to MCTsMCNs

Structure of IPMTs/IPMNs

Numerous cystic dilatations of branch pancreatic ducts with epithelial hyperplasia appear together due to parenchymal atrophy/loss, resulting in a 'multilocular cyst' appearance (fig. 6); this causes confusion between IPMTs and MCTs [13]. Such cystic dilatations of the branch duct with hyperplasia are very similar to the branch duct type of IPMT (fig. 7) as follows: papillary

a

Fig. 7.IPMT in the branch duct (68-year-old female). a MRCP showing cystic/branchlike dilatation of the branch duct and mild dilatation of the main pancreatic duct. b Cut surface, consisting of cystic dilatation of pancreatic ducts. c Low magnification showing cystic dilatation of branch duct with parenchymal loss, resulting in 'multilocular cyst' appearance. HE. X 12.5.

Fig. 7.IPMT in the branch duct (68-year-old female). a MRCP showing cystic/branchlike dilatation of the branch duct and mild dilatation of the main pancreatic duct. b Cut surface, consisting of cystic dilatation of pancreatic ducts. c Low magnification showing cystic dilatation of branch duct with parenchymal loss, resulting in 'multilocular cyst' appearance. HE. X 12.5.

arrangement, luminar mucin retention, surrounding parenchymal atrophy and highly frequent occurrence in elderly subjects: except for cellular atypism [2], and some hyperplasia that happen to show clinical pictures similar to IPMTs. Hence, both lesions are considered a series of, or relevant to, the ductal lesions.

Difference in Hyperplasia and Adenoma

With regard to the pathological determination of intraductal proliferation, the difference between hyperplasia and IPMT is very complicated. In a study of benign small intraductal tumors found incidentally at autopsy, Ratcliffe et al. [14] discusses the difficulty in morphologically distinguishing these branchtype IPMTs from ductal papillary hyperplasia found in normal and chronically

Fig. 8. Well developed papillary hyperplasia. a-c Hyperplasia showing double structures, consisting of papillary proliferation overlying pyloric gland-like tubuli beneath. a HE. X125. b Immunostained with MUC5AC. X200. c Immunostained with MUC6. X200.

inflamed pancreatic tissue and in association with a pancreatic tumor. However, in our opinion, well developed papillary hyperplasia of the pancreatic duct shows a characteristic two-layered structure with papillary growth overlying pyloric gland-like tubuli beneath, whereas adenoma, even if fully developed, consists of only simple papillary growth without pyloric gland-like tubuli (fig. 8). This structure is described by the WHO [15] as follows: mucinous cell hypertrophy in medium-sized ducts may be associated with pyloric gland metaplasia in small glands surrounding the larger duct. The former two-layered structure has a mucinous characteristic similar to the gastric pyloric area mucosa: foveo-lar epithelium and pyloric glands which stain positive for galactose oxidase-cold thionine Schiff-paradoxical concanavalin A (GOCTS-PCS) [16], while the latter does not. Immunohistochemically, the overlying papillary proliferation is positive for MUC5AC, while the pyloric gland-like tubuli beneath stain with MUC6 (fig. 8b, c). Hence, epithelial hyperplasia and adenoma differ in structure, mucin histochemistry and MUC immunohistochemistry.

Table 1. Differences between branch type IPMTs and MCTs

Branch type IPMT

Gender

Location

Structure

Capsula

Ductal communication Macroscopic view Epithelium Stroma elderly male head preserved/undeviated absent (pancreatic duct wall) present middle-aged female body and tail deviation/exophytic protrusion present usually absent cystic (dilatation of duct)

mucinous fibrous cystic mucinous ovarian-like stroma

IPMT = Intraductal papillary-mucinous tumor; MCT = mucinous cystic tumor.

Differential Diagnosis between IPMT and MCT

MCTs are unilocular or multilocular cystic tumors, which are composed of mucinous epithelium and ovarian-like stroma. In cases of multilocular cystic tumor, there was no apparent interlocular communication. The MCT sometimes communicated with the main pancreatic duct [17].

MCTs tend to occur in middle aged women, and are located in the body and tail of the pancreas, while IPMTs tend to occur most frequently in elderly men, and are located in the head, similar to mucous cell metaplasia/hyperplasia [4], as shown in table 1. Hence, MCTs are different from IPMTs.

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