Sentinel Lymph Node identification with a fluorescent dye in colorectal cancer: a comparison of two injection techniques

M Ankersmit, MSc, Jwj de Haan, Mhgm van der Pas, MD, Majm Jacobs, MD, PhD, Nct van Grieken, MD, PhD, Wjhj Meijerink, MD, PhD. VU University Medical Center, Amsterdam, The Netherlands.

We present a novel technology for laparoscopic sentinel lymph node (SLN) mapping in colorectal cancer patients. The sentinel lymph node (SLN) procedure is a standard staging technique in several types of cancer. One of the major problems of SLN mapping in colorectal cancer is the lack of an optimal dye and technique for identification of the nodes. In this study we used the Near-Infrared (NIR) dye Indocyanin Green (ICG) to identify nodes with a newly developed NIR laparoscope. We compared two different injection techniques; subserosal and submucosal injection.

Methods and procedures
Patients planned for a laparoscopic resection of a colorectal carcinoma without distant metastases were included. Dye was injected in the subserosa or submucosa of the bowel. Ten minutes after injection we searched for fluorescent nodes with the NIR laparoscope. Fluorescent nodes were harvested and analyzed by the pathologist using H&E and additional immunohistochemistry.

A total of 25 patients were included. The dye was injected in the subserosa in 14 patients and in the submucosa in 11 patients. In all patients that were injected in the subserosa, we identified at least one fluorescent node, non of which was positive for metastases. In 4/14 patients, non-fluorescent regional nodes were positive for metastases.
Using the submucosal injection technique, 9/11 patients showed at least one fluorescent node, in 6 patients these were negative for metastases. Of the remaining three patients, the fluorescent lymph was positive for metastasis in one. Another node, negative on fluorescence but positive for metastasis, was identified in that same patient. In the other two patients, fluorescent positive nodes contained isolated tumour cells as only indication of metastatic disease. In 2/11 we could not identify fluorescent nodes. In one of these patients the pathologist identified three solitary tumour nodi > 3 mm considered as lymph node metastasis.

Laparoscopic identification of the SLN in colorectal cancer seems possible by using the NIR-dye ICG. Results of the submucosal injection were more reliable compared to the subserosal injection. With some difficulties to overcome, submucosal injection of ICG appears a promising technique in the identification of colorectal lymph nodes.
A future study will focus on combining a fluorescent dye with a radioactive tracer to improve tissue penetration, to enable pre-operative visualization of the SLN and improves detectability during the operation.

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