Selective endoscopic nasobiliary drainage to determine the resection range for intraductal papillary neoplasm of the bile duct with an initially indeterminate primary site

BACKGROUND: Intraductal papillary neoplasm of the bile duct (IPNB) often presents with marked ductal dilatation due to excessive mucin secretion, which can make it challenging to distinguish the primary tumor site from secondary dilatation. CASE PRESENTATION: An 83-year-old woman presented with obstructive jaundice and bilateral biliary dilatation. Initial imaging, including CT, MRI, and PET-CT, failed to localize the tumor. While the first peroral cholangioscopy (POCS) was unsuccessful due to viscous bile, a second POCS identified a papillary lesion distal to the confluence of the B2 and B3 bile ducts. To determine the appropriate resection range, an endoscopic nasobiliary drainage (ENBD) tube was selectively placed in the right hepatic duct. The drainage of normal-colored, non-viscous bile and subsequent resolution of jaundice suggested that the right-sided dilatation was caused by mucin reflux from the left liver, rather than direct tumor involvement. The patient successfully underwent a curative left hepatectomy, including caudate lobectomy. Histopathology confirmed type 1 IPNB with high-grade atypia (carcinoma in situ) and negative surgical margins. CONCLUSION: POCS combined with selective ENBD may provide a valuable strategy for determining the surgical extent in mucin-producing IPNB when the primary site is difficult to identify using conventional imaging.