Pancreaticobiliary Maljunction With a Non‐Dilated Extrahepatic Bile Duct Masked by Adenomyomatosis: A Potential Cause of Unresectable Gallbladder Carcinoma

Adenomyomatosis of the gallbladder (ADM) is generally considered benign. The presented cases were initially diagnosed with ADM via ultrasound during an annual health check-up and monitored for several years without further investigations due to the absence of significant changes or symptoms. Subsequently, one case was diagnosed with pancreaticobiliary maljunction (PBM) with a non-dilated extrahepatic bile duct (EBD) after symptom onset, and underwent prophylactic laparoscopic cholecystectomy to avoid the risk of carcinogenesis. Although the other case remained asymptomatic, ultrasound later revealed far-advanced gallbladder carcinoma with direct invasion into the liver and hepatic metastases, and endoscopic retrograde cholangiopancreatography identified PBM with a non-dilated EBD. At laparotomy, she was found to have unresectable disease and died 4 months later. ADM associated with PBM has been recently reported. Consequently, evaluating the presence or absence of PBM is essential for determining an appropriate treatment strategy when diagnosing ADM.