Anatomical descriptions of lymphatic channels and drainage into a porta lymph node were first described in 1907 by Jameson et al.1 2 Over the years, sentinel lymph node (SLN) mapping has been used to treat melanoma, breast cancer, cervical cancer, and other types of tumors. Indocyanine green (ICG) is a water-soluble tricarbocyanine dye that was first used in medicine for blood saturation studies.3

In endometrial cancer, the combination of ICG, near infra red (NIR) and SLN has been widely accepted as the gold standard for initial tumor staging. Comparisons between comprehensive staging and the SLN algorithm have demonstrated the superiority of the method in detecting positive nodes, with shorter surgeries and fewer complications.4 These results are a combination of the greater probability of the tracer identifying the first ‘porta’ detecting the lymph node, and the greater probablity of receiving the first metastasis (SLN) associated with increased quality of pathologic analysis with ultrastaging. Intra-operative detection of SLNs requires knowledge of minimally invasive and ICG mapping principles. Fluorescent highlights of lymphatic pathways occur because of a combination of near-infrared light (NIR) emission and captioning. Deviations in the concentration, dispersion of tracer, and incidence of light might interfere with the detection.

One example is the exploration of deeper nodes in patients with a high body mass index. If not correctly explored, lymphatic pathways will not receive NIR light, thus never exhibiting the classic fluorescent green light (Figure 1). Uterine lymphatics may vary into three distinct pathways. The first and most common pathway is the upper paracervical pathway (UPP) toward the obturator area and iliac vessels. The secondary and less common lower paracervical pathway (LPP) crosses the pararectal space toward the presacral/para-aortic area. A third, more common pathway called the infundibulum pelvic pathway (IPP) occurs when the tracer is injected at the fundus.5

Obturator sentinel lymph node and secondary external iliac node. SLN, sentinel lymph node.

This video compilation (Video 1) of 54 endometrial cancer SLN approaches demonstrates the principles of ICG, NIR, and the distinctive intra-operative findings of SLN. The majority of findings demonstrated a highlighted pathway finishing at a highlighted SLN. Finding a highlighted pathway terminating into a non-highlighted pathway raises the concern of a potentially compromised node. In 80–85% of cases, the tracer dispersed into one UPP at each hemipelvis. Parallel LPP occurs in 15–20% of cases. If present, the primary lymph node in this path should also be considered an SLN.

Correct SLN mapping requires careful pathway tracking from the paracervix until the appearance of the first lymph node. Premature ICG injection tends to highlight several lymph nodes along the route. Therefore, finding a highlighted lymph node does not result in an SLN. This pathway must be explored to identify deeper, real SLNs. The technique of SLN mapping demands careful exploration of ICG spread into lymphatic channels.

Data are available upon request.

Not applicable.

This study involves human participants and was approved by Institute of Cancer of the State of São Paulo. Plataforma BrasilCAAE: 42103120.2.0000.0068Instituição. Proponente: FUNDACAO FACULDADE DE MEDICINA. Patrocinador Principal: SECRETARIA DE ESTADO DA SAUDE. Participants gave informed consent to participate in the study before taking part.