Figure 1. Macroscopic picture of the left lobe of the liver. Dilation of intrahepatic bile ducts is seen without mass lesion. Wonkyung Jung, et al. Biliary intraepithelial neoplasia: a case with benign biliary stricture 329 showing variable degree of atypia (Fig. 2). Epithelial cells lining these lesions were mostly flat, but in some foci, they showed micropapillary or tufted appearance. Pseudostratification of nuclei was commonly finding. Variations in nuclear size, nuclear membrane irregularity and abnormally large nuclei are also noted. Invasion of basal lamina was not observed. This patient was finally diagnosed as biliary intraepithelial neoplasia. DISCUSSION BilIN is not infrequently encountered in routine pathologic practice. In surgically removed liver samples of chronic biliary disease and chronic liver disease such as hepatolithiasis, primary sclerosing cholangitis, choledochal cyst, chronic hepatitis C, and alcoholic cirrhosis, BilINs can be found without difficulty and in which condition, the incidence of cholangiocarcinoma is high.3-5 BilINs are also frequently found in adjacent to invasive cholangiocarcinomas and the incidence of BilIN-3 lesion parallels that of invasive cholangiocarcinoma suggesting that BilIN could be precursor lesion of invasive cholangiocarcinoma.1 There is a report A D B E C F Figure 2. Histologic features of bile duct epithelium lining dilated bile ducts. (A, B) Normal epithelium and biliary intraepithelial neoplasia (BilINs) are observed. (C) Normal biliary epithelia show monolayer of columnar cells without pseudostratification. (D) Focal nuclear pseudostratification and nuclear elongation are noted. Nuclear sizes and shapes are relatively uniform (BilIN-1). (E) This lesion shows tufted epithelial structure. Nuclear enlargement and irregular nuclear membrane are evident (BilIN-2). (F) Cytologic and nuclear abnormality including loss of polarity, nuclear enlargement and nuclear membrane irregularity are evident. There is no invasion of basement membrane (BilIN-3). (A and B: hematoxylin and eosin (H&E), ×40; C-F: H&E, ×400).