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Nakamura et al. Mini-invasive Surg 2022;6:50 https://dx.doi.org/10.20517/2574-1225.2022.38 Page 9 of 20

Because the anatomical shape of the stomach varies per individual, even in the same case, the appropriate
positioning may change depending on the time and conditions. In particular, the shape of the stomach is
affected by the amount of air inside, so it is better to pay attention to the extent of the lumen during the
procedure and control the air volume by insufflation and deflation buttons. It is sometimes necessary to be
flexible by switching the ESD knives or patient position during the gastric ESD procedure.

The appropriate position also depends on the type of ESD knife used. The operation field needs to be
adjacent to the needle-type or scissor-type knives, while close positioning is not absolutely necessary for
partially insulated knives. Therefore, in areas where close scope positioning is difficult, such as the gastric
anterior wall or lesser curvature of the lower corpus, partially insulated knives are preferred.

Marking
The marking is performed 2-3 mm (approximately the width of the device sheath) outside using a needle-
type knife with electrocautery under the careful image-enhanced endoscopic observation of the tumor
boundary. Chromoendoscopy using indigo carmine and magnifying narrow-band imaging (NBI) share
[8]
similar diagnostic accuracies for the delineation of early gastric cancer . If there is a suspicious area
adjacent to the lesion, it is included in the removal area; therefore, markings are made on an area diagnosed
as definitely non-neoplastic outside the lesion. Then, a mucosal incision is performed outside the marking
to completely remove the lesion and suspicious mucosa. In patients receiving H. pylori eradication therapy,
a tumor will show surface differentiation , and the tumor surface may be partially covered with non-
[9]
[10]
neoplastic epithelium . Therefore, the tumor boundary is often unclear. It is preferable to add an extra
margin for such lesions. In the case of a tumor with an unclear margin even under chromoendoscopic or
magnifying NBI observation, a mapping biopsy is performed from the mucosa outside the suspicious tumor
boundary. When biopsy results are negative, markings are made on the negative biopsy scars, and the
mucosa outside the marking is incised. Markings can be applied subsequently around the lesion or initially
in areas with clear demarcation and secondarily to areas between these markings. The marking interval is
usually 2-3 mm or shorter, so the next marking is seen in the endoscopic view during mucosal incision. To
orient the oral or anal side of the lesion in the resected specimen, extra markings can be placed on the oral
or anal side as landmarks.

Submucosal injection
Submucosal fluid injection is performed just outside of the markings, where the mucosal incision is
intended. Creating an adequate mucosal lift is important for safe ESD. The types of fluid used for
submucosal injection include normal saline, glycerol, and sodium hyaluronate. Hypertonic solutions or
viscous fluids are preferred because they elevate the mucosa more and maintain mucosal elevation longer
[11]
than that by normal saline . Submucosal injections should be administered into the appropriate layer. In
general, injection into the shallow submucosa creates a high elevation for mucosal incision, whereas
injection into the deep submucosa facilitates recognition of the deep submucosal plane for submucosal
dissection. After puncturing the target mucosa, the needle tip is slightly maneuvered inside the submucosa
to find the proper submucosal plane while the solution is injected. Once good elevation is achieved, the
needle tip is planted in the same submucosal plane. Fine movement of the needle tip enables control of the
blob creation direction. Puncture of the base of the previous elevation makes the subsequent injection
smoother. As the injection solution is reabsorbed over time, injection and subsequent mucosal incision in
large lesions are performed in multiple sessions instead of injecting the solution into the entire
circumference in one session.