Bile duct adenoma and von Meyenburg complex-like duct arising in hepatitis and cirrhosis: pathogenesis and histological characteristics

Ancillary tests for hepatobiliary neoplasms: what we know and what we need to know

Ancillary tests are commonly used in the surgical pathology setting for diagnosing challenging neoplastic diseases of the liver and biliary tract, while histology and clinical correlation remain to be critically important. With continuous discoveries, more and more useful ancillary tests have become available, which can help distinguish between malignant and benign hepatocellular neoplasms, malignant and benign biliary tract entities, and intrahepatic and metastatic carcinomas. This review will focus on existing and emerging biomarkers (such as glutamine synthetase, organic anion transporting polypeptide 1B3, insulin-like growth factor-II mRNA binding protein-3, S100P, SMAD4, enhancer of zeste homolog 2, albumin, hepatocyte nuclear factor-1β, etc.) that can be used for the diagnosis, classification and prognostication of hepatobiliary neoplasms.

Morphological aspects of small-duct cholangiopathies: A minireview

The biliary system consists of intrahepatic and extrahepatic bile ducts lined by biliary epithelial cells (cholangiocytes). Bile ducts and cholangiocytes are affected by a variety of disorders called cholangiopathies, which differ in aetiology, pathogenesis, and morphology. Classification of cholangiopathies is complex and reflects pathogenic mechanisms (immune-mediated, genetic, drug- and toxin-induced, ischaemic, infectious, neoplastic), predominant morphological patterns of biliary injury (suppurative and non-suppurative cholangitis, cholangiopathy), and specific segments of the biliary tree affected by the disease process. While the involvement of large extrahepatic and intrahepatic bile ducts is typically visualised using radiology imaging, histopathological examination of liver tissue obtained by percutaneous liver biopsy still plays an important role in the diagnosis of cholangiopathies affecting the small intrahepatic bile ducts. To increase the diagnostic yield of a liver biopsy and determine the optimal therapeutic approach, the referring clinician is tasked with interpreting the results of histopathological examination. This requires knowledge and understanding of basic morphological patterns of hepatobiliary injury and an ability to correlate microscopic findings with results obtained by imaging and laboratory methods. This minireview describes the morphological aspects of small-duct cholangiopathies pertaining to the diagnostic process.

Benign biliary neoplasms and biliary tumor precursors

Benign biliary tumor are common lesions that are often an incidental finding in subjects who undergo medical imaging tests for other conditions. Most are true neoplasms while few result from reactive or malformative proliferation. Benign tumors have no clinical consequences, although the premalignant nature or potential for malignant transformation is of concern in some cases. The main practical problem for pathologists is the need to differentiate them from malignant biliary tumours, which is not always straightforward. Premalignant lesions of the bile duct have been described, although their incidence has been poorly characterized. These lesions include biliary mucinous cystic neoplasms, intraductal papillary neoplasms of the bile duct, and biliary intraepithelial neoplasia. In this article, histopathology of benign biliary tumors and biliary tumor precursors is discussed, with a focus on the main diagnostic criteria.

Bile duct adenoma may be a precursor lesion of small duct type intrahepatic cholangiocarcinoma

BACKGROUND/AIMS

Precursor lesions of small duct type intrahepatic cholangiocarcinoma (small duct iCCA) have not been clarified so far. We hypothesised that precursor lesions may be frequently distributed in the background liver of small duct iCCA.

METHODS AND RESULTS

We determined by histology the presence of bile duct adenomas and von Meyenburg complexes as candidate precursor lesions in the background liver of small duct iCCA, with other primary liver carcinomas as control. Subjects included 28 patients with small duct iCCA, 29 with large duct iCCAs, 60 with combined hepatocellular-cholangiocarcinoma (Comb) and 40 with hepatocellular carcinoma (HCC). The prevalence of bile duct adenomas in the background liver was significantly higher in small duct iCCA (35.7%) compared to other primary liver carcinomas (Comb, 4.9%; 10%, HCC) (P < 0.01). The prevalence of bile duct adenomas was significantly associated with the presence of von Meyenburg complexes and ductal plate malformation-like patterns in small duct iCCAs and Combs. Von Meyenburg complexes were detected in 11 small duct iCCA (39.3%), five large duct iCCAs (17.2%), 10 Comb (16.4%) and 13 HCC (33.3%), respectively (P > 0.05). Small duct iCCAs showed altered expression of ARID1A (46.4%), p53 (39.3%), PBRM1 (14.3%), IMP3 (85.7%) and EZH2 (82.1%), whereas these markers were negative in bile duct adenomas.

CONCLUSION

Bile duct adenomas may be precursor lesions of small duct iCCAs. Alteration of ARID1A, p53 or PBRM1 may be involved in the carcinogenesis of small duct iCCAs.

Bile duct adenoma: imaging features and radiologic-pathologic correlation

PURPOSE

This study aimed to reveal characteristic imaging features of bile duct adenoma (BDA) by radiologic-pathologic correlation.

MATERIALS AND METHODS

We retrospectively analyzed pathological and imaging findings of seven patients with BDA.

RESULTS

The median maximum diameter of BDA was 5.5 mm. Six lesions had hemispheric morphology. Seven lesions were located in the liver subcapsular region, and proliferation of bile ductules without atypia and fibrous stroma was observed. Two lesions had different microscopic findings. In both lesions, proliferation of bile ductules without atypia was observed in the margin. In one lesion, the percentage of fibrosis and hyalinization was higher at the center than at the margin. In the other lesion, inflammatory cell infiltration was observed in the center. On contrast-enhanced imaging, BDAs showed hypervascularity in the early phase and prolonged enhancement in the delayed phase. On contrast-enhanced multidetector computed tomography during hepatic arteriography, two lesions showed ring-like enhancement in the first phase and prolonged enhancement in the second phase. These were the different histopathologic features of BDAs between the margin and center.

CONCLUSION

Bile duct adenoma can be characterized as a small semicircular lesion located in the liver subcapsular region, which show hypervascularity in the early phase with prolonged enhancement.

Cholangiocarcinoma: Classification, Histopathology and Molecular Carcinogenesis

Cholangiocarcinoma (CC) is the second most common tumor of the liver, originating from the biliary system with increasing incidence and mortality worldwide. Several new classifications review the significance of tumor localization, site of origin, proliferation and biomarkers in the intrahepatic, perihilar and distal forms of the lesion. Based on growth pattern mass-forming, periductal-infiltrating, intraductal, undefined and mixed types are differentiated. There are further subclassifications which are applied for the histological features, in particular for intrahepatic CC. Recognition of the precursors and early lesions of CC including biliary intraepithelial neoplasia (BilIN), intraductal papillary neoplasm of the bile ducts (IPNB), biliary mucinous cystic neoplasm (MCNB) and the candidate precursors, such as bile duct adenoma and von Meyenburg complex is of increasing significance. In addition to the previously used biliary markers detected by immunohistochemistry, several new markers have been added to the differentiation of both the benign and malignant lesions, which can be used to aid in the subclassification in association with the outcome of CC. Major aspects of biliary carcinogenesis have been revealed, yet, the exact way of this diverse process is still unclear. The factors contributing to molecular cholangiocarcinogenesis include various risk factors, different anatomical localizations, multiple cellular origins, genetic and epigenetic alterations, tumor microenvironment, heterogeneity and clonal evolution. Driver mutations have been identified, implying that they are optimal candidates for targeted therapy. The most promising therapeutic candidates have entered clinical trials.

Mucins: the Old, the New and the Promising Factors in Hepatobiliary Carcinogenesis

Mucins are large O-glycoproteins with high carbohydrate content and marked diversity in both the apoprotein and the oligosaccharide moieties. All three mucin types, trans-membrane (e.g., MUC1, MUC4, MUC16), secreted (gel-forming) (e.g., MUC2, MUC5AC, MUC6) and soluble (non-gel-forming) (e.g., MUC7, MUC8, MUC9, MUC20), are critical in maintaining cellular functions, particularly those of epithelial surfaces. Their aberrant expression and/or altered subcellular localization is a factor of tumour growth and apoptosis induced by oxidative stress and several anti-cancer agents. Abnormal expression of mucins was observed in human carcinomas that arise in various gastrointestinal organs. It was widely believed that hepatocellular carcinoma (HCC) does not produce mucins, whereas cholangiocarcinoma (CC) or combined HCC-CC may produce these glycoproteins. However, a growing number of reports shows that mucins can be produced by HCC cells that do not exhibit or are yet to undergo, morphological differentiation to biliary phenotypes. Evaluation of mucin expression levels in precursors and early lesions of CC, as well as other types of primary liver cancer (PLC), conducted in in vitro and in vivo models, allowed to discover the mechanisms of their action, as well as their participation in the most important signalling pathways of liver cystogenesis and carcinogenesis. Analysis of mucin expression in PLC has both basic research and clinical value. Mucins may act as oncogenes and tumour-promoting (e.g., MUC1, MUC13), and/or tumour-suppressing factors (e.g., MUC15). Given their role in promoting PLC progression, both classic (MUC1, MUC2, MUC4, MUC5AC, MUC6) and currently tested mucins (e.g., MUC13, MUC15, MUC16) have been proposed to be important diagnostic and prognostic markers. The purpose of this review was to summarize and update the role of classic and currently tested mucins in pathogenesis of PLC, with explaining the mechanisms of their action in HCC carcinogenesis. It also focuses on determination of the diagnostic and prognostic role of these glycoproteins in PLC, especially focusing on HCC, CC and other hepatic tumours with- and without biliary differentiation.

Subcentimetric Incidental Intrahepatic Cholangiocarcinoma in an Explant Liver: Diagnostic Difficulty of a Rare Entity

Incidental intrahepatic cholangiocarcinoma (iCCA) is a rare neoplastic lesion in the explant liver specimens with an approximate incidence of 0.7%. The detection of iCCA is associated with poor prognosis in the posttransplant setting. The occurrence of a subcentimetric iCCA is very rare and poses a major diagnostic challenge to the pathologist. This article presents a rare case of subcentimetric iCCA in a young male in the background of advanced stage chronic liver disease resulting from autoimmune hepatitis possibly with chronic cholangiopathy along with the histomorphological differentials.

Pediatric Mesenchymal Hamartomas of the Liver can Show Both Foregut and Hindgut Phenotype

Cystic epithelium in mesenchymal hamartoma (MH) is typically biliary type. Mucinous differentiation of the epithelium and increased hepatocellular component may pose a diagnostic challenge. We studied MH in 7 children (6 M, 1 F; age 4 months to 8 years, median 1 year). Resected tumors varied from 3.0 to 17.0 cm. All tumors showed biliary epithelium in the cystic component with strong and diffuse reactivity for CK7 and CK19. Expression of CK20 and CDX2 was additionally seen in 2 tumors, rare/focal in 1, and diffuse with mucinous differentiation in the other. Strong and continuous nuclear reactivity for Sox9 was seen in the cyst epithelium in all 7 tumors including focal staining in mucinous areas. It was also positive in the hepatocellular component. CD56 and vimentin were variably positive in the cystic epithelium of all cases. Alpha-fetoprotein showed patchy weak staining in the hepatocellular component and was negative in the cystic epithelium. Hepar-1 showed focal staining in the cystic epithelium in 4/7 cases and diffuse in the hepatocellular component. Both patients showing CK20 and CDX2 expression had abnormal chromosomal analysis: one with balanced translocation between chromosomes 2 and 19 and other with loss of chromosome Y. Among others, one showed 46,XY,inv(9)(p11q12), one did not grow cells, and the remaining 3 had normal karyotype. Six patients underwent resection and one had liver transplantation. All were alive and well with a median follow-up of 1.5 years. In conclusion, mucinous epithelium can be seen in MH. Expression of Sox9 in the cyst epithelium and hepatocytes suggests a common origin for these components. Expression of vimentin indicates an overlapping epithelial-mesenchymal phenotype. Hepatic MH can show divergent epithelial differentiation including both foregut and hindgut phenotype, which may provide insights into the pathogenesis of this rare neoplasm but does not seem to affect the outcome in this limited series.

Latest advances in the pathological understanding of cholangiocarcinomas

Cholangiocarcinomas (CCAs) are anatomically classified into intrahepatic, perihilar, and distal types. The gross pathological classification of intrahepatic CCAs divides them into mass-forming, periductal-infiltrating, and intraductal-growth types; and perihilar/distal CCAs into flat- and nodular-infiltrating and papillary types. Unique preinvasive lesions appear to precede individual gross types of CCA. Biliary intraepithelial neoplasia, a flat lesion, precedes periductal-, flat-, and nodular-infiltrating CCAs, whereas intraductal papillary neoplasm of the bile duct (IPNB) precedes the intraductal-growth and papillary type of CCAs. IPNBs are heterogeneous in their histological and pathological profiles along the biliary tree. Hepatobiliary cystadenomas/adenocarcinomas are reclassified as cystic IPNBs and hepatic mucinous cystic neoplasms. Peribiliary glands may participate in the development of CCAs. These latest findings present a new challenge for understanding the pathology of CCAs.

Albumin expression distinguishes bile duct adenomas from metastatic adenocarcinoma

AIMS

Bile duct adenomas may be difficult to distinguish from metastatic carcinomas, particularly well-differentiated pancreatic ductal adenocarcinoma. Prior studies have evaluated the utility of various immunohistochemical markers, although these markers are notable for low sensitivity and/or specificity. The aim of this study was to investigate the utility of albumin and BRAFV600E expression in distinguishing between metastatic pancreatic adenocarcinoma and bile duct adenoma.

METHODS AND RESULTS

We studied 26 bile duct adenomas, three bile duct hamartomas, and 158 pancreatic ductal adenocarcinomas. Branched-chain in-situ hybridization (bISH) for albumin was performed; bISH is based on the branched DNA technology, wherein signal amplification is achieved via a series of sequential steps. Additionally, BRAFV600E immunohistochemistry (IHC) was performed on a subset of cases. Twenty-three of 25 (92%) bile duct adenomas were positive for albumin; 18 (72%) showed diffuse staining, and five showed focal staining (20%), including two challenging examples. Two bile duct hamartomas also stained positively. All pancreatic adenocarcinomas were negative for albumin. Seven of 16 (44%) bile duct adenomas and five of 106 (5%) pancreatic ductal adenocarcinomas were positive for BRAFV600E by IHC. The sensitivity and specificity of expression of albumin, as detected by bISH, for distinguishing bile duct adenomas from metastatic pancreatic adenocarcinomas were 92% and 100%, respectively; the sensitivity and specificity of BRAFV600E IHC for distinguishing bile duct adenomas from metastatic pancreatic adenocarcinomas were 43.8% and 95.3%, respectively.

CONCLUSIONS

Diagnostically challenging examples of bile duct adenoma may be distinguished from metastatic pancreatic adenocarcinoma by the use of albumin bISH.