Many patients with early gastric cancer are currently treated with advanced laparoscopic gastrectomy procedures, such as laparoscopy-assisted distal gastrectomy (LADG) and laparoscopy-assisted total gastrectomy, in many countries.^1–4 Advanced laparoscopic gastrectomy contributes to both better aesthetics and early postoperative recovery.⁵ However, the patients’ quality of life (QOL) is mainly affected by late phase complications, such as dumping syndrome and body weight loss resulting from disturbances in oral intake. Therefore, both a minimal invasive approach for early-phase recovery and satisfactory late-phase function after gastric cancer surgery should be carefully considered in patients indicated for these procedures.

Although function-preserving gastrectomy, such as partial gastrectomy, segmental gastrectomy, and proximal gastrectomy, with limited stomach resection and lymph node dissection may help to improve postoperative late phase function, a certain incidence of skip metastasis in the first or third compartment of regional lymph nodes remains an obstacle to the wider application of these procedures. To overcome these issues, the concept of sentinel node (SN) mapping is anticipated to become a novel diagnostic tool for the identification of clinically undetectable lymph node metastasis in patients with early gastric cancer.^6–8

Sentinel nodes are defined as the first draining lymph nodes from the primary site of a tumor⁶ and are thought to be the first possible site of micrometastasis along the route of lymphatic drainage from the primary lesion. Therefore, the pathological status of SNs can theoretically predict the status of all regional lymph nodes. If SNs are recognizable and negative for cancer metastasis, unnecessary radical lymph node dissection can be avoided. SN navigation surgery is defined as a novel, minimally invasive surgery based on SN mapping and the SN-targeted diagnosis of nodal metastasis. This surgery can prevent unnecessary lymph node dissection, thus preventing associated complications and improving the patients’ QOL.

Sentinel node mapping and biopsy were first applied to patients with melanoma and breast cancer and were subsequently extended to patients with many other solid tumors.^6–8 The clinical application of SN mapping for early gastric cancer has remained controversial for years. However, results from single institutional studies, including those from our report and those from a recent multicenter trial of SN mapping for early gastric cancer, are considered acceptable in terms of the SN detection rate and the accuracy of determination of the lymph node status.^9,10 On the basis of these results, we developed a novel, laparoscopic, minimally invasive gastrectomy technique combined with SN mapping.

A dual-tracer method that utilizes radioactive colloids and blue dyes is currently considered the most reliable method for the stable detection of SNs in patients with early gastric cancer.^10,11 The accumulation of radioactive colloids facilitates the identification of SNs even in resected specimens, and the blue dye is effective for the intraoperative visualization of lymphatic flow, even during laparoscopic surgery. Technetium-99m tin colloid, technetium-99m sulfur colloid, and technetium-99m antimony sulfur colloid are preferentially used as radioactive tracers, while isosulfan blue, patent blue, and indocyanine green (ICG) are the currently preferred choices as dye tracers.

In our institution, we perform SN mapping and biopsy for clinical T1 (or T2) tumors, primary lesions less than 4 cm in diameter, and clinical stage N0 gastric cancer. In our procedures, 2.0 mL (15 MBq) technetium-99m tin colloid solution is injected the day before surgery into four quadrants of the submucosal layer of the primary tumor site using an endoscopic puncture needle to facilitate accurate tracer injection. Because of its relatively large particle size, technetium-99m tin colloid accumulates in the SNs after local administration.

The first step in laparoscopic intraoperative SN detection performed at our institution involves the injection of the ICG dye tracer under the guidance of intraoperative endoscopy, similar to the preoperative injection of the radioactive tracer.^11,12 The ICG dye tracer is injected into four quadrants of the submucosal layer of the primary site using an endoscopic puncture needle, and within 15 minutes after injection, blue-stained lymphatic vessels and lymph nodes are identifiable laparoscopically. ICG facilitates the visualization of lymphatic vessels despite several issues, such as the fast movement of the dye and blind sites in dense fat. Simultaneously, a hand-held gamma probe (GPS Navigator; RMD Instruments LLC, Watertown, MA, USA) is used to locate radioactive SNs. Intraoperative gamma probing is feasible in laparoscopic gastrectomy using a special gamma detector introducible from trocar ports. In general, radio-guided methods allow the confirmation of a complete SN harvest using gamma probing. In contrast, the dye procedure enables real-time observation of lymphatic flow. We currently recommend a combination of blue dyes and radio-guided methods for systematic SN mapping in patients with early gastric cancer.

For intraoperative SN sampling, the pick-up method is well established for the detection of melanoma and breast cancer. However, it is recommended that the clinical application of intraoperative SN sampling should include sentinel lymphatic basin dissection, which is best described as a sort of focused lymph node dissection involving hot and blue nodes.^10,11 Gastric lymphatic basins can be divided in the following five directions along the main arteries: the left gastric artery area, right gastric artery area, left gastroepiploic artery area, right gastroepiploic artery area, and posterior gastric artery area.¹³

On the back table, the resected sentinel lymphatic basin is carefully examined for detection of hot lymph nodes (i.e., SNs) using the hand-held gamma probe. Blue-stained or radioactive SNs identified in the resected specimens are carefully confirmed using the gamma probe, and all SNs are sent for intraoperative pathological examination. After gastrectomy, the presence or absence of other radioactive SNs among the residual lymph nodes in the upper abdominal cavity is investigated using the gamma probe, which is inserted from the trocar port or a small abdominal wound.

Indocyanine green is known to have excitation and fluorescence wavelengths in the near-infrared range.¹⁴ Very recently, some investigators have suggested the use of infrared ray electronic endoscopy (IREE) to demonstrate the clinical utility of intraoperative ICG infrared imaging as a new tracer for laparoscopic SN biopsy^14,15 (Fig. 96-1A, B). IREE might be a useful tool to improve the visualization of ICG-stained lymphatic vessels and SNs even in adipose tissue. More recently, ICG fluorescence imaging has shown promise as a novel technique for SN mapping, as SNs can be clearly visualized by ICG fluorescence imaging in comparison with visualization by the naked eye^16,17 (Fig. 96-1C, D). Hence, these new technologies might revolutionize SN mapping procedures not only for gastric cancer, but also for many other solid tumors.