Abstract
RATIONALE: Biliary intraepithelial neoplasm (BilIN) is characterized by a microscopically identifiable preinvasive neoplasm of the biliary tract. BilIN is rarely diagnosed intentionally and is often detected incidentally in surgical specimens obtained via surgical resection for other types of cancers. Herein, we report a rare case of high-grade BilIN localized in the distal bile duct. PATIENT CONCERNS: A 67-year-old female patient presented with epigastric discomfort approximately 1 month earlier. The patient underwent a blood test on the previous day at a local hospital. Results revealed abnormal liver function. Thus, the patient was referred to our hospital for further examination and treatment. DIAGNOSES: Blood tests showed elevated hepatic and biliary enzyme levels. However, jaundice was not noted, and the patient's tumor marker levels were normal. Contrast-enhanced computed tomography scan revealed dilatation of the common bile duct and diffuse wall thickening of the bile duct and gallbladder walls. Tissue samples obtained via bile juice cytology showed a poorly differentiated adenocarcinoma. However, the bile duct walls were thick, and the tumor location was unclear. Hence, peroral cholangioscopy was performed. Results revealed an irregular mucosal surface and low papillary protuberances in the lower bile duct. Based on these findings, the patient was diagnosed with distal bile duct carcinoma. INTERVENTIONS: She underwent surgical resection. OUTCOMES: Histological findings showed high-grade BilIN with scattered low-grade BilIN in the surrounding area. LESSONS: We present a rare case of high-grade BilIN in the lower bile duct that was detected without other types of cancers and diagnosed via peroral cholangioscopy.