The sentinel node is the lymph node where the lymphatic flow from the primary tumor first enters. For the identification of the sentinel node, the dye method (injection of visible dye such as indigocarmine and indocyanine green (ICG) around the primary lesion) and/or radioisotope (RI) method (injection of 99mTc tin colloid, etc.) have been used. The dual tracer method (concomitant use of the dye method and the RI method) has recently been regarded as a standard because the dye method alone is associated with relatively high false-negative results due to fat tissues around the nodes. The use of fluorescence imaging following an injection of ICG may enhance the detectability of the sentinel node because near-infrared fluorescence signals can penetrate fat tissues up to about 10 mm. In addition, ICG fluorescence imaging has advantages over the RI technique in that it does not need the radiation exposure of the patient and medical staff, and the hurdles of handling radioactive isotopes (e.g., the need to maintain the endoscope set in a radiation-controlled area).

The advantage of the RI technique is that the particle size of 99mTc tin colloid is large and most of the particles stay in the sentinel node. In contrast, in the ICG fluorescence method, the particles are so fine that they pass through the sentinel node and secondary and tertiary lymph nodes. Therefore, it is important to observe the timing and distributions of fluorescence signals following an injection of ICG in order to identify the sentinel lymph node accurately [1]. Among various protocols of ICG fluorescence imaging for sentinel node navigation, the method introduced by Kinami et al. [2] [injection of 100-fold dilution (50 μg/mL ICG)] around the gastric cancer on a day before surgery, as demonstrated in Chap. 21, seems to be associated with favorable outcomes and may be useful in the surgical procedures for other organs. When the resected specimens are observed by fluorescence imaging according to Kinami’s protocol, a lot of lymph nodes can be identified with different fluorescence intensities. Since ICG can be accumulated in the lymph nodes gradually over the course of a day, we can consider the node with the highest fluorescence intensity as the sentinel lymph node [3,4,5].

Chapter 24 also illustrates the use of ICG fluorescence imaging for lymphography and evaluation of lymphedema, which has been inspired by the sentinel node identification methods. Nowadays, ICG fluorescence imaging has widely been used as an essential technique for the evaluation and treatment of lymphoedema. This would be a good example indicating that cross-sectional exchange of information among specialties is indispensable for the development of new surgical techniques like intraoperative fluorescence imaging.