Sentinel lymph node mapping as a side-effect of colonoscopic tattooing

Correct tumor localization is crucial for proper surgical therapy in colorectal cancer. Intraoperative visualization of the lesion is facilitated by preoperative colonoscopic tattooing, regardless of whether an open or laparoscopic approach is employed.

This pilot study tests the hypothesis that colonoscopic tattooing can serve the additional role of sentinel lymph node (SLN) mapping.

We collected 5 prospective and 16 retrospective cases, in which colonoscopic tattooing was applied and surgery was performed. Nineteen of these cases showed colorectal cancer. High-grade intraepithelial neoplasia was found in two cases. All lymph nodes (LNs) were histologically assessed for metastasis and carbon particles, and those that tested positive were registered as carbon-containing lymph nodes (CcLNs). Subsequently, additional step sections were cut and immunohistochemistry was performed on all lymph nodes of the malignant cases.

A total number of 311 lymph nodes were investigated. CcLNs could be identified in 17 of 21 cases (detection rate: 81%). The histomorphology of CcLNs was identical to that known from carbon as a sentinel marker dye. The mean CcLN number was 2 +/- 2 (range 1-6). After primary evaluation, one metastasis was detected in a case where a CcLN was not observed. All other cases showed no positive LNs. After step sectioning and immunohistochemical staining, one additional micrometastasis was found in a CcLN, resulting in upstaging from N0 to N1 (mi).

Our findings support the thesis that colonoscopic tattooing holds the potential for SLN mapping. Therefore, a prospective study with an appropriate case number should follow this pilot study to clarify the clinical value of this finding.