Distal cholangiocarcinoma arising in a Choi Type I septate common bile duct: a case report.

Septate common bile duct (CBD) is a rare congenital anomaly resulting from incomplete recanalization of the primitive biliary tract. Although often asymptomatic, it predisposes to bile stasis, chronic inflammation, and potential malignant transformation. Distal cholangiocarcinoma arising in association with a septate CBD is exceptionally rare. We report the case of an 84-year-old male presenting with progressive jaundice, right hypochondrial pain, anorexia, and 20 kg weight loss over 2 months. Examination revealed icterus and a palpable non-tender mass. Laboratory studies showed marked hyperbilirubinemia (total bilirubin 11 mg/dl). Ultrasonography demonstrated a 2.5 × 2.0 cm mass in the CBD/pancreatic head region causing obstruction. Magnetic resonance cholangiopancreatography (MRCP) identified a malignant distal CBD stricture with proximal dilatation and a longitudinal septum, consistent with Choi Type I septate CBD. The patient was diagnosed with distal cholangiocarcinoma and scheduled for pancreaticoduodenectomy. Recognition of rare biliary anomalies is crucial, with high-resolution MRCP guiding safe resection and reconstruction.