Background and Objectives: The prognosis of biliary tract carcinoma remains poor despite aggressive surgical approaches. Factors contributing to the dismal outcomes include the high rates of lymph node (LN) metastasis in advanced biliary tract carcinomas. In particular, paraaortic LN metastasis affects the indication for resection of biliary tract cancers, because a failure of surgical resection to improve the prognosis has been reported in cases showing paraaortic LN metastasis. Although the size of LNs is one of the major factors distinguishing positive from negative nodes, size is not a reliable indicator of metastasis because many small LNs contain metastasis and the quantity of cancer cells in metastatic LNs is variable. In biliary cancers, few studies have addressed the histological features of LN metastasis. Therefore, this study analyzed the detailed morphological features of metastatic LNs in biliary cancers.
Methods: This study investigated 496 dissected LNs including 112 paraaortic LNs from 47 patients with biliary cancers. The diameter of the long axis (size) and the histological ratio of the metastatic area were measured using H&E staining by computer analysis software WinRoof.
Results: Among 496 nodes, 51 nodes (10.3%) had metastatic lesion. The mean sizes of LN with metastasis were significantly larger than those of nodes without metastasis (9.5mm vs. 6.5mm). However, twelve nodes (23.5%) with metastasis were less than 5mm. The optimal cut-off size of positive LNs judged from receiver operator characteristic curve was 7.5mm, but the sensitivity was low (60.8%). The ratio of the metastatic area significantly correlated with the size of metastatic LNs (p=0.023). In paraaortic LNs, 8 nodes (7.1%) had metastatic lesion among 112 nodes. There was no correlation between size and the presence of metastasis or the ratio of metastatic area in paraaortic LNs. Preoperative CT could evaluate 25% of metastatic paraaortic LNs that had a large ratio of metastatic area.
Conclusions: Although large sizes of LNs are highly suggestive of metastasis, there were many small nodes with metastasis. Because the presence of LNs with a low ratio of metastatic area may result in a low sensitivity of preoperative detection, a new modality will be required to diagnose LN metastasis in biliary tract cancers.