Does Congenital Biliary Dilatation Todani Type II (Diverticular Type) Really Exist?

AIM OF THE STUDY: The aim of the study is to clarify the clinicopathological and biliary morphological characteristics in reported cases of diverticular congenital biliary dilatation (CBD). METHOD: Using PubMed and the Japan Medical Abstracts Society, articles on possible diverticular CBD were extracted and the clinical pictures examined. We also sought evidence for definitions of diverticular CBD and the associated condition of pancreaticobiliary maljunction (PBM) using the original articles by Alonso-Lej and Todani. The characteristic biliary morphologies of cases with images were also investigated. RESULTS: Analyses of 211 possible cases superficially demonstrated multiple diverticula in 12 (12%) and single diverticulum in 89 (88%), with diverticula located in the upper (n = 38, 38%), middle (n = 32, 32%), or lower (n = 26, 26%) biliary tract in and presence of intra-diverticular stones, PBM, and biliary carcinoma in 23% (n = 18), 39% (n = 25), and 11% (n = 14), respectively. However, evidence defining diverticular CBD or justifying the lack of associated PBM was not demonstrated even in the original articles. Scrutiny of the biliary anatomy in 59 cases with images showed incorrect inclusions of types I or IV-A with an irregular biliary duct wall or dilated cystic duct, periampullary choledochal diverticula, or even solitary biliary cysts. Authentic diverticular CBD, representing the diverticulum connected to the middle of the common bile duct via a thin, patent stalk was seen in only 6 cases. CONCLUSION: Real diverticular CBD appears extremely rare. The lack of an objective definition allows wide interpretations of clinical pictures, creating inconsistencies in the diagnosis and treatment of CBD and raising questions regarding the utility of conventional classifications. LEVEL OF EVIDENCE: Level III.

Anatomical patterns of biliary atresia including hepatic radicles at the porta hepatis influence short- and long-term prognoses.

BACKGROUND/PURPOSE: The biliary atresia (BA) inflammatory process leads to various obstructive patterns of extrahepatic biliary trees. The significance of the various BA obstructive patterns is unclear. This study aimed to determine the relationship between the anatomical patterns of the biliary tract and short- and long-term prognoses in BA. METHODS: Between 1989 and 2018, 3483 patients were registered in the Japanese Biliary Atresia Registry. For this study, we selected 2649 patients who underwent Kasai portoenterostomy (KP) between the ages of 31 and 90 days to eliminate the influence of age at KP as much as possible. RESULTS: Regarding the main type, there were significant differences in the jaundice clearance rate (JCR; Type I: 67.9%, Type I-cyst: 79.4%, Type II: 74.5%, Type III: 60.9%; P < .0001) and the native liver survival rate (NLSR; P < .0001). In subgroups with hepatic radicles in Types I, II, and I-cyst, there was a significant difference in JCR (P = .0004) and NLSR (P = .0026). In subgroups with hepatic radicles in Type III, there was a significant difference in JCR (P = .0148) and NLSR (P = .0421). CONCLUSIONS: Anatomical patterns of obstruction influenced short- and long-term prognoses in BA. These patterns were suggested to be prognostic factors following KP.

Pancreaticobiliary maljunction and congenital biliary dilatation.

Pancreaticobiliary maljunction is a congenital malformation in which the pancreatic and bile ducts join outside the duodenal wall, usually forming a long common channel. Because the action of the sphincter of Oddi does not regulate the function of the pancreaticobiliary junction in patients with pancreaticobiliary maljunction, two-way regurgitation occurs. Reflux of pancreatic juice into the biliary tract is associated with a high incidence of biliary cancer. Biliary carcinogenesis in patients with pancreaticobiliary maljunction is thought to follow the hyperplasia, dysplasia, then carcinoma sequence due to chronic inflammation caused by pancreatobiliary reflux. Pancreaticobiliary maljunction is diagnosed when an abnormally long common channel is evident on imaging studies. Congenital biliary dilatation involves both local dilatation of the extrahepatic bile duct, including the common bile duct, and pancreaticobiliary maljunction. Extrahepatic bile duct resection is the standard surgery for congenital biliary dilatation. However, complete excision of the intrapancreatic bile duct and removal of stenoses of the hepatic ducts are necessary to prevent serious complications after surgery.

Classification of pancreaticobiliary maljunction and clinical features in children.

BACKGROUND: In 2015, the Committee on Diagnostic Criteria of the Japanese Study Group on Pancreaticobiliary Maljunction (PBM) proposed a classification of PBM into four types: (A) stenotic type, (B) non-stenotic type, (C) dilated channel type, and (D) complex type. To validate this classification and clarify the clinical features of the four types of PBM, a retrospective multicenter study was conducted. METHODS: The study group of 317 children with PBM was divided into the four types of PBM. Clinical features, preoperative complications, operations, and postoperative pancreatic complications were evaluated. RESULTS: All patients underwent excision of the extrahepatic bile duct. In type A, the age was younger and there was a higher incidence of cystic dilatation. Non-dilatation of the common bile duct was frequently seen in type B. Abdominal pain with hyperamylasemia was frequently seen in types B and C. In particular, the incidence of protein plugs and biliary perforation was high in type C (56.1% and 14.3%, respectively). The overall incidence of acute pancreatitis was 7.3%. Pancreatitis after excisional surgery was rare in the children in this study. Two patients with type D (0.6%) developed chronic pancreatitis postoperatively. CONCLUSIONS: This proposed classification is simple and correlates well with clinical features.

Japanese clinical practice guidelines for congenital biliary dilatation.

Until now, there have been no practical clinical guidelines for congenital biliary dilatation (CBD). In this review article, the Japanese Study Group on Congenital Biliary Dilatation (JSCBD) propose to establish clinical practice guidelines for CBD. Because the evidence-based literature is relatively small, we decided to create guidelines based on the consensus of experts, using the medical literature for reference. A total of 20 clinical questions (CQs) were considered by the members of the editorial committee responsible for the guidelines. The CQs included the distinct aspects of CBD: (1) Concepts and Pathology (three CQs); (2) Diagnosis (six CQs); (3) Pancreaticobiliary Complications (three CQs); Treatments and Prognosis (eight CQs). Each statements and comments for CQs were made by the guidelines committee members. CQs were finally approved after review by members of the editorial committee and the guidelines evaluation board of CBD. These guidelines were created to provide assistance in the clinical practice of CBD management; their contents focus on clinical utility, and they include general information on CBD to make this disease more widely recognized.

Long-term outcomes after revision of Kasai portoenterostomy for biliary atresia.

BACKGROUND: The indications for and efficacy of revision of portoenterostomy (PE) for biliary atresia (BA) needs to be reassessed in an era of liver transplantation. We therefore reviewed the long-term outcomes following revision of PE. METHODS: This was a retrospective study of the medical records of patients with BA who underwent PE and revision of PE. We investigated the role of revision on outcomes of jaundice-free native liver survival (approval number: 2015-0094). RESULTS: Portoenterostomy was performed in 76 patients, among whom 22 underwent revision. Revision for recurrent jaundice was performed for four of 51 patients, who were transiently jaundice free after initial PE, but only one achieved native liver survival. Revision for repeated cholangitis in two patients achieved native liver survival over 10 years. Revision was performed in 16 of the 25 patients in whom initial PE failed; of these, four survived with their native liver (ages 3, 12, 12, and 14 years). The PE revision did not significantly affect liver transplantation duration and survival outcome. CONCLUSIONS: Revision of PE was suitable for repeated cholangitis. Revision for recurrent jaundice, regardless of whether the initial PE was successful, could have a limited but positive effect in preventing long-term progressive liver failure.

Diagnostic criteria for congenital biliary dilatation 2015.

BACKGROUND: The Diagnostic Criteria for Pancreaticobiliary Maljunction 2013 were published by the Japanese Study Group on Pancreaticobiliary Maljunction (JSGPM) in 2014. The committee of JSGPM for diagnostic criteria for pancreaticobiliary maljunction has established the standard diameter of the bile duct, and a definition of dilatation of the bile duct was proposed in 2014. METHODS: The committee of JSGPM prepared the diagnostic criteria for congenital biliary dilatation in 2014, and a final revised version was approved in 2015. RESULTS: Congenital biliary dilatation is defined as a congenital malformation involving both local dilatation of the extrahepatic bile duct, including the common bile duct, and pancreaticobiliary maljunction. However, cases associated with intrahepatic bile duct dilatation can also be included. Various kinds of pathological conditions can occur on hepatobiliary systems and pancreas by bile duct dilatation and pancreaticobiliary maljunction. For a diagnosis of congenital biliary dilatation, both abnormal dilatation of the bile duct and pancreaticobiliary maljunction must be evident by either imaging test or anatomical examination. Acquired or secondary dilatation of the bile duct by obstruction due to biliary stones or malignancy should be strictly excluded. CONCLUSION: Diagnostic criteria for congenital biliary dilatation 2015 were established from Japan representing a world first.

Usefulness and safety of endoscopic retrograde cholangiopancreatography in children with pancreaticobiliary maljunction.

BACKGROUND: To assess the diagnostic ability and safety of endoscopic retrograde cholangiopancreatography (ERCP) in in-depth preoperative examination of children patients with pancreaticobiliary maljunction (PBM). METHODS: In 63 patients with a definite diagnosis of PBM, the ability to visualize the bile and main pancreatic ducts was compared between ERCP, which was performed in 63 patients with a definite diagnosis of PBM, and magnetic resonance cholangiopancreatography (MRCP), which was performed before ERCP in 29 patients. For ERCP, its complications were also evaluated. RESULTS: The intrahepatic bile ducts could be visualized using ERCP in 44 patients (69.8%) and using MRCP in 18 (62.1%). The extrahepatic bile ducts could be visualized using ERCP in 59 patients (93.7%) and using MRCP in 29 (100%). The rates of the visualization of the main pancreatic duct and pancreaticobiliary ductal union were significantly higher in using ERCP than in using MRCP (96.8 vs. 41.4% and 90.5 vs. 37.9%, respectively; P<0.0001). As complications, hyperamylasemia developed in 12 patients (19%), but no other severe complications such as pancreatitis were observed. CONCLUSIONS: ERCP as part of an in-depth preoperative examination of children with PBM is useful and safe.

Pancreatobiliary reflux in individuals with a normal pancreaticobiliary junction: a prospective multicenter study.

BACKGROUND: Pancreatobiliary reflux (PBR) can occur in individuals without pancreaticobiliary maljunction. The aim of this study was to elucidate the incidence of PBR in individuals with a normal pancreaticobiliary junction and its impact on the biliary tree. METHODS: Data were prospectively collected from 15 centers on 420 patients with a morphologically normal pancreaticobiliary junction who had undergone bile sampling and measurement of the biliary amylase level. We investigated the incidence and predictive factors for high biliary amylase levels (HBAL), as well as the relationship of HBAL with biliary malignancy. RESULTS: Twenty-three patients (5.5%) showed HBAL (≥10,000 IU/L). Univariate analysis showed that risk factors for the elevation of biliary amylase levels were the existence of a relatively long common channel (≥5 mm), acute pancreatitis, and papillitis. Multivariate analysis revealed that only the existence of a relatively long common channel was a significant factor for PBR. Biliary amylase levels in patients with a relatively long common channel were significantly higher than in patients without a long common channel (12,333 vs. 2,070 IU/L, P = 0.001). The incidence of HBAL (P < 0.001), as well as the overall biliary amylase levels (P = 0.007) were significantly higher in patients with gallbladder cancer than in those without gallbladder cancer. CONCLUSIONS: The PBR was frequently observed in individuals with a relatively long common channel. Patients showing HBAL with normal pancreaticobiliary junction are at high risk for gallbladder cancer.

Recent advances and problems in the management of pancreaticobiliary maljunction: feedback from the guidelines committee.

Clinical practice guidelines on how to deal with pancreaticobiliary maljunction (PBM) were made in Japan in 2012, representing a world first. Using a narrow definition, congenital biliary dilatation involves only Todani type I (except type Ib) and type IV-A, both of which are accompanied by PBM in almost all cases. Prospective ultrasonographic study revealed that the maximum diameter of the common bile duct increased with age. Pathophysiological conditions due to pancreatobiliary reflux occur in patients with high confluence of the pancreaticobiliary ducts, a common channel ≥ 6 mm long and occlusion of communication during contraction of the sphincter of Oddi. Since PBM can be diagnosed by magnetic resonance cholangiopancreatography, multi-planar reconstruction multi-detector row computed tomography and endoscopic ultrasonography, the current diagnostic criteria should be revised to take these diagnostic imaging modalities into consideration. According to a nationwide survey, biliary cancer occurred in 21.6% of adult patients with PBM with biliary dilatation and 42.2% of patients with PBM without biliary dilatation. In biliary cancer associated with PBM without biliary dilatation, 88.1% were gallbladder cancer. Treatment for PBM with biliary dilatation is prophylactic flow-diversion surgery, but further investigations and surveillance studies are needed to clarify the appropriate surgical strategy for PBM without biliary dilatation.

Endoscopic biliary drainage for children with persistent or exacerbated symptoms of choledochal cysts.

BACKGROUND: Symptoms of choledochal cysts sometimes persist or become exacerbated. As preoperative management for patients with these cysts, we prospectively employed endoscopic drainage, based on the theory that protein plugs cause symptoms by obstructing the pancreatobiliary ducts. METHODS: Children with choledochal cysts underwent endoscopic retrograde cholangiopancreatography (ERCP). When ERCP showed compaction with filling defects in patients with persistent or worsening symptoms (study patients), the placement of a short biliary stent tube was attempted for drainage. The clinical and ERCP findings of the study patients were compared with those of patients who were asymptomatic at ERCP (asymptomatic patients). RESULTS: There were 13 study patients (median age 2.9 years) and 41 asymptomatic patients (4.7 years) enrolled in the study between August 2005 and February 2011. Study patients more frequently had jaundice and elevated transaminase levels. ERCP showed that all study patients had obstruction or compacted filling defects in the common channel or the narrow segment distal to the cyst. Insertion of a stent tube was successful in 11 patients. Symptoms were relieved soon after biliary drainage. Surgery revealed that the obstructing materials were protein plugs, except in one case, which involved fatty acid calcium stones. CONCLUSIONS: These results support the protein plug theory. Endoscopic short-tube stenting is adequate and effective as preoperative management.

Identification of Epstein-Barr virus-infected CD27+ memory B-cells in liver or stem cell transplant patients.

To analyse the phenotype of Epstein-Barr virus (EBV)-infected lymphocytes in EBV-associated infections, cells from eight haematopoietic stem cell/liver transplantation recipients with elevated EBV viral loads were examined by a novel quantitative assay designed to identify EBV-infected cells by using a flow cytometric detection of fluorescent in situ hybridization (FISH) assay. By this assay, 0.05-0.78% of peripheral blood lymphocytes tested positive for EBV, and the EBV-infected cells were CD20+ B-cells in all eight patients. Of the CD20+ EBV-infected lymphocytes, 48-83% of cells tested IgD positive and 49-100% of cells tested CD27 positive. Additionally, the number of EBV-infected cells assayed by using FISH was significantly correlated with the EBV-DNA load, as determined by real-time PCR (r2  = 0.88, P < 0.0001). The FISH assay enabled us to characterize EBV-infected cells and perform a quantitative analysis in patients with EBV infection after stem cell/liver transplantation.

Gene expression profiling reveals upregulated UCA1 and BMF in gallbladder epithelia of children with pancreaticobiliary maljunction.

BACKGROUND: Pancreaticobiliary maljunction is usually associated with choledochal cysts and often causes biliary carcinoma; however, the mechanism of carcinogenesis remains unknown. No study has analyzed overall changes in genetic expression beginning during childhood in gallbladder epithelia with pancreaticobiliary maljunction. PATIENTS AND METHODS: The genomewide expression of gallbladder epithelia was analyzed in 6 children with pancreaticobiliary maljunction and in 4 pediatric controls. Selected genes that were expressed differentially were further analyzed by the real-time reverse transcription-polymerase chain reaction (RT-PCR). The products of upregulated genes confirmed by real-time RT-PCR were immunohistochemically analyzed using gallbladders from 19 children with pancreaticobiliary maljunction, 5 pediatric controls, and 5 children with gallstones. RESULTS: Microarray analysis identified 188 upregulated and 160 downregulated genes. RT-PCR confirmed upregulation in 5 of 6 genes and downregulation in 1 of 5 genes, including UCA1, DUOX2, DUOXA2, ID1, BMF, and GP2. Immunohistochemistry showed a significantly higher expression of BMF in the pancreaticobiliary maljunction patients than in the controls and gallstone patients. CONCLUSIONS: This study identified several deregulated genes in the gallbladder of children with pancreaticobiliary maljunction, which may contribute to the pathophysiology. UCA1, a noncoding RNA, is an oncofetal gene, and its upregulation may be important for biliary carcinogenesis. The elevated expression of BMF may function as an apoptotic activator in proliferative gallbladder epithelia.

Biliary reconstruction with wide-interval interrupted suture to prevent biliary complications in pediatric living-donor liver transplantation.

BACKGROUND/PURPOSE: Liver transplantation is an established therapy for children with end-stage chronic liver disease or acute liver failure. However, despite refinements of surgical techniques for liver transplantation, the incidence of biliary tract complications has remained high in recent years. Therefore, we suggest our anastomotic technique with wide-interval interrupted suture to prevent biliary complications in pediatric living-donor liver transplantation (LDLT). METHODS: Forty-nine LDLTs were performed on 49 pediatric recipients with end-stage liver disease. Biliary reconstruction was performed using a 2.5× magnifying surgical loupe, via end bile duct to side Roux-en-Y hepaticojejunostomy (n = 47) and duct-to-duct choledochocholedochostomy (n = 2) with an external stent. A stay suture with 6-0 absorbable materials was placed at each end of the anastomotic orifice. Two interrupted sutures of the posterior row were performed. After completion of the suture of the posterior row, an external transanastomotic stent tube was inserted into the intrahepatic bile duct and was fixed with posterior row material. Finally, two interrupted sutures of the anterior wall were performed, totaling six stitches. The transanastomotic stent tube emerging out of the blind end of the Roux-en-Y limb was covered with a round ligament and was usually left in place for 1 month after the operation. RESULTS: The median follow-up period was 58.0 months (range 8-135 months). In 33 recipients, the bile duct was used to perform the reconstruction with a single lumen. In 5 cases, there were 2 bile ducts that were formed to enable a single anastomosis. In 10 cases, there were 2 separated ducts and each duct was anastomosed with the recipient jejunum. In one case, there were 3 ducts that were formed to enable two anastomoses. Twenty-two percent of the living-donor grafts required 2 biliary anastomoses. Forty-four patients (89.8%) are alive (ranging from 8 months to 11 years), and 5 patients have died. Two patients had biliary complications, an anastomotic stricture in one (2.0%) and bile leakage in one. There were no complications due to anastomotic tubes. CONCLUSIONS: Biliary reconstruction with wide-interval interrupted suture prevents anastomotic strictures and bile leakage in pediatric LDLT.

Embryology of the biliary tract.

A hepatic diverticulum appears in the ventral wall of the primitive midgut early in the 4th week of intrauterine life in the development of the human embryo. This small diverticulum is the anlage for the development of the liver, extrahepatic biliary ducts, gallbladder, and ventral pancreas. By the 5th week, all elements of the biliary tree are recognizable. Marked elongation of the common duct occurs with plugging of the lumen by epithelial cells. Recanalization of the lumen of the common duct starts at the end of the 5th week and moves slowly distally. By the 6th week, the common duct and ventral pancreatic bud rotate 180 degrees clockwise around the duodenum. Early in the 7th week, the bile and pancreatic ducts end in closed cavities of the duodenum. Between the early 8th and 12th week, hepatopancreatic ducts have both superior and inferior orifices. Of these two orifices, the inferior one is usually suppressed. The muscle of the sphincter of Oddi develops from a concentric ring of mesenchyme surrounding the preampullary portion of the bile and pancreatic ducts. At about the 10th week, the muscle of the sphincter of Oddi undergoes differentiation. In the 16th week, the muscularis propria extends from just outside the fenestra to the upper end of the ampulla. By the 28th week, the musculus proprius is differentiated almost to the distal end of the ampulla.

Immunologic and virologic analyses in pediatric liver transplant recipients with chronic high Epstein-Barr virus loads.

BACKGROUND: Long-term Epstein-Barr virus (EBV) monitoring for potentially life-threatening posttransplant lymphoproliferative disorder (PTLD) has identified asymptomatic patients who maintain high EBV loads over long periods. METHODS: Thirty-one pediatric liver transplant recipients were designated as 11 chronic high EBV load carriers (EBV DNA level >5000 copies/mL of whole blood for >6 months) and 20 control recipients. Serial quantification of EBV DNA, measurement of interleukin 10 (IL-10) concentrations, EBV-specific tetramer staining, and relative quantification of EBV gene expression in peripheral blood mononuclear cells were performed. RESULTS: Most of the chronic high EBV load carriers were seronegative at transplant, the median time to resolution of a chronic high EBV load was 23 months, and no recipient developed late-onset PTLD. EBV DNA was detected predominantly in CD19(+) cells. The plasma concentration of IL-10 and the EBV-specific CD8(+) cell frequency did not differ significantly between the chronic high EBV load carriers and the control recipients. Analysis of gene expression showed that EBV-encoded small RNA 1, BamHI A rightward transcripts, and latent membrane protein 2 were positive in peripheral blood mononuclear cells from chronic high EBV load carriers. CONCLUSIONS: EBV-infected cells in the blood of chronic high EBV load carriers expressed a highly restricted set of latency genes, suggesting that the EBV-infected cells escaped from a T cell response.

Pancreatobiliary reflux and the length of a common channel.

BACKGROUND/PURPOSE: Gallbladder cancer occurs frequently in patients with pancreaticobiliary maljunction due to pancreatobiliary reflux. Pancreatobiliary reflux is also detected in some patients with a relatively long common channel. This study aimed to clarify the correlation between pancreatobiliary reflux and the length of a common channel. METHODS: Two hundred and three patients, in whom both the length of a common channel and amylase level in the bile were measured, were enrolled from nine centers. RESULTS: Bile amylase level was correlated with the length of a common channel (P < 0.01). The minimum length of a common channel that could induce a markedly elevated amylase level in the bile (>1,000 mg/dl) was determined as 5 mm. We redefined high confluence of pancreatobiliary ducts (HCPBD) as cases with a common channel > or = 5 mm, in which the communication between the pancreatic and bile ducts was occluded with the sphincter contraction. Gallbladder cancer was found in 20% of 56 redefined HCPBD patients. Bile amylase level >1,000 mg/dl and biliopancreatic reflux were detected in 79 and 95% of the patients, respectively. CONCLUSIONS: Patients with a common channel > or = 5 mm (redefined HCPBD) should be monitored for the development of gallbladder cancer, as they frequently showed significant pancreatobiliary reflux.

Thoracoscopic lobectomy for congenital cystic lung diseases in neonates and small infants.

BACKGROUND: There are still few reports on thoracoscopic lobectomy in neonates. The rate of prenatally diagnosed congenital cystic lung diseases is increasing, and such diseases appear to be a good indication for thoracoscopic lobectomy. METHODS: We performed a prospective trial of thoracoscopic lobectomy for all congenital cystic lung diseases in children. Complete thoracoscopic lobectomy was performed by employing carbon dioxide insufflation without single lung ventilation. The results were analyzed, comparing patients with pre- and postnatal diagnoses. RESULTS: Seven patients were prenatally diagnosed with congenital pulmonary airway malformations (CPAM) between January 2008 and August 2009, and all but one underwent surgery during the neonatal period (prenatal group). Nine patients underwent surgery after infection subsided due to lesions (7 CPAM, 2 intrapulmonary sequestration) postnatally identified by infection presence (median 2 years; range 15 days to 14 years) (postnatal group). The prenatal group showed a significantly lower rate of adhesions, shorter operation time, and smaller volume of blood loss. There were two conversions in the postnatal group. There were two postoperative complications (persistent air leak and phrenic nerve paralysis) in the prenatal group. The esthetic results were good. CONCLUSIONS: Thoracoscopic lobectomy for congenital cystic lung diseases in neonates was practicable, with good esthetic results. Dissection was easier with significantly less blood loss in patients without adhesions, even in neonates. However, this procedure necessitated highly skilled endoscopic maneuvers within a small working space.

Papillary hyperplasia of the gallbladder in pancreaticobiliary maljunction represents a senescence-related lesion induced by lysolecithin.

Cellular senescence, an irreversible growth arrest, is considered to play as safeguard against malignant progression, though such a mechanism is speculative in human carcinogenesis. In gallbladder carcinoma, cholecystolithiasis and pancreaticobiliary maljunction (PBM) are major risk factors. Here, by using 113 surgically resected gallbladders and cultures of human gallbladder epithelial cells (HGECs) and gallbladder carcinoma cell line (TGBC2TKB), we examined carcinogenesis with respect to cellular senescence. Among 15 cases of PBM in which carcinoma was found in 4 cases, nonneoplastic gallbladder mucosa showed diffuse papillary hyperplasia (PHP). PHP was not found in gallbladders with cholecystolithiasis. Interestingly, PHP exhibited senescent features such as expression of p16(INK4A) and low cell proliferative activity. In contrast, EZH2, a polycomb group protein, was overexpressed in intraepithelial neoplasm and carcinoma in gallbladders with cholecystolithiasis. In PBM, EZH2 was expressed only in carcinoma foci but not in PHP. Cultured HGECs treated with lysolecithin, the level of which is elevated in gallbladder bile of PBM, showed increased expression of p16(INK4A) and senescence-associated beta-galactosidase. Conversely, enforced overexpression of EZH2 in senescent HGECs reduced p16(INK4A) expression. A knockdown of EZH2 in cultured TGBC2TKB cells increased p16(INK4a) expression. In conclusion, PHP in PBM may act as a barrier to malignant transformation for decades. EZH2 may be responsible for the escape from cellular senescence followed by malignant transformation in the gallbladder of PBM.