The histopathological evaluation based on the indocyanine green fluorescence imaging of regional lymph node metastasis of splenic flexural colon cancer by near-infrared observation.

Purpose: The purpose of this study was to investigate the relationship between the fluorescence on indocyanine green fluorescent imaging (ICG-FI) and the histopathological findings of regional lymph node (LN) metastasis of splenic flexural colon cancer.

Methods: From July 2013 to December 2018, consecutive patients with splenic flexural colon cancer with a preoperative diagnosis of N0 who underwent laparoscopic surgery were enrolled. The distribution of cancer sites in metastatic LNs (completely/not completely occupied by metastatic foci) was evaluated with hematoxylin and eosin-stained preparations. We compared the relationship between the distribution of cancer site and fluorescence of paraffin block in metastatic LNs.

Results: Seventy-two patients were enrolled, of whom 13 (18.1%) had metastatic LNs. A total of 25 metastatic LNs were evaluated. The median short axis of the occupied LNs was 4.5 mm, which was significantly larger than that of the non-occupied LNs (3.0 mm; p = 0.036). In the near-infrared observation of the paraffin block, the completely occupied LNs showed no fluorescence, regardless of the LN size, but 8 of 10 non-occupied LNs showed fluorescence (p < 0.001). Even the non-occupied LNs that showed fluorescence, the cancer site did not show fluorescence.

Conclusions: The occupied LNs showed no fluorescence, but 80% of the non-occupied LNs showed fluorescence. Even in non-occupied LNs that showed fluorescence, the cancer site did not show fluorescence. This demonstrated LN dissection should not be omitted, even if no fluorescence is noted on intraoperative ICG-FI.