Adenomyomatous hyperplasia of the extrahepatic bile duct: a systematic review of a rare lesion mimicking bile duct carcinoma.

Adenomyomatous hyperplasia (AH) is a tumor-like inflammatory hyperplastic lesion. In the biliary system, AH commonly arises in the gallbladder, but AH of the extrahepatic bile duct is extremely rare. AH usually develops and is found with symptoms related to biliary stenosis or obstruction, but there are few disease-specific manifestations. It is difficult to make a definitive diagnosis by imaging or cytopathological examination; thus, surgical resections were performed in all past reported cases. The pathophysiological etiology of AH is unknown, but it is considered to be associated with chronic inflammation. According to the epidemiological findings of cases reported to date, the possibility of malignant transformation is considered to be negative. However, the symptoms and imaging findings of AH are difficult to distinguish from those of early-stage bile duct carcinoma. In the current review, we discuss the epidemiology, pathophysiology, diagnosis, and management of AH of the bile duct.