Abstract
ABSTRACT
Biliary intraepithelial neoplasia (BilIN) is a precursor of bile duct adenocarcinoma that arises in the setting of chronic biliary or liver disease. Because BilIN spreads as a flat or micropapillary lesion, it is difficult to detect by imaging, and biopsy interpretation is often complicated by inflammation or prior instrumentation. Consequently, clinical knowledge remains limited, and standardized diagnostic protocols are lacking. A patient presented with acute cholangitis due to common bile duct (CBD) stones. During plastic stent placement, endoscopic retrograde cholangiopancreatography revealed irregular narrowing of the distal CBD. Peroral cholangioscopy (POCS) showed micropapillary epithelium extending from the bifurcation to the distal duct, progressively thickening the lumen. Pancreatoduodenectomy was performed, and pathology confirmed BilIN‐3 with carcinoma in situ. Although BilIN has been visualized by POCS, most reports were descriptive. In this case, characteristic POCS findings guided pancreatoduodenectomy despite nondiagnostic biopsies. The clear correlation between POCS morphology and the final diagnosis underscores the clinical value of cholangioscopy in managing indeterminate distal bile duct strictures.