A Case of IPNB in which the Presence of Tertiary Lymphoid Structures Made IDUS Diagnosis Difficult

Abstract

A woman in her 70s was referred for evaluation of a cystic liver lesion and bile duct dilation. Imaging revealed a cystic lesion communicating with B3 and a nodular enhancement, suggesting intraductal papillary neoplasm of the bile duct (IPNB). ERCP indicated mucus, and contrast imaging confirmed a cyst conected to B3. IDUS showed asymmetric wall thickening from B4 to the left hepatic duct, suggesting superficial spread. A left hepatectomy was performed, and pathology confirmed IPNB with papillary growth and mucus production. However, the suspected spread was limited to B3, while irregular wall thickening was due to submucosal lymphocyte infiltration, identified as tertiary lymphoid structures (TLS). TLS, ectopic lymphoid organs in chronic inflammation, complicated IDUS assessment. This case highlights the impact of TLS on preoperative staging and the need for careful interpretation.