Characterization of high-grade biliary intraepithelial neoplasm of the gallbladder in comparison with intracholecystic papillary neoplasm.

Biliary intraepithelial neoplasm (BilIN) is characterized by a microscopically identifiable preinvasive neoplasm of the biliary tract. In this study, the high-grade BilIN of gallbladder was examined pathologically and compared with the intracholecystic papillary neoplasm (ICPN) of gallbladder. Sixteen high-grade BilINs (height <0.5 cm) collected from 2297 cholecystectomies (0.7%) and another three cases (19 cases total) were examined and compared with 34 cases of ICPN (greatest diameter ≥1 cm and height ≥0.5 cm). High-grade BilINs were incidentally found in 11 cholecystectomies, and the remaining eight were cholecystectomized in cases with a preoperative diagnosis of carcinoma. The largest diameter ranged from 0.5 to 6 cm. While 13 cases were recognized grossly as clustered granular and rough mucosa, the remaining were almost unrecognizable. Histologically, the high-grade BilINs showed intraepithelial neoplastic growth. Furthermore, they frequently showed intraepithelial replacement growth to non-neoplastic glands and cystic lesions in the gallbladder. The lesions presented with flat, wave or fold-like patterns, including tubular components. Short papillary components were also found in 13 cases. Gastric and biliary subtypes were frequent. Several foci of stromal invasion were found in the short papillary components in three cases. The lower polypoid or granular parts of conglomerated ICPNs showed intraepithelial neoplastic lesions sharing many features with high-grade BilINs with short papillary components. In conclusion, high-grade BilINs showed intraepithelial growth of neoplastic epithelia involving the mucosa. A morphologic continuum was noted between high-grade BilINs with short papillary components and conglomerated ICPNs, suggesting that conglomerated ICPNs may arise from high-grade BilINs with short papillary components.

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