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Yoshizaki et al. Mini-invasive Surg 2022;6:17 https://dx.doi.org/10.20517/2574-1225.2021.116 Page 3 of 9

[18]
coagulation with a low high-frequency power setting using an Endo-Knife [Figure 1].

Fibrosis in the submucosa
The degree of fibrosis in the submucosa has a significant impact on procedure time and safety [19,20] .
However, it is impossible to accurately determine the degree of fibrosis before ESD. Even if there is severe
fibrosis in the submucosa, high-quality ESD must be performed. The basic strategy for fibrosis is to dissect
around the fibrosis at an appropriate depth between the vascular network and the musclaris propria. In the
fibrotic area, the border between the myofiber bundle and the fibrotic area is carefully identified using local
injection, and three techniques (sliding/scooping/tapping) are used for precise dissection [21,22] [Figure 2].

Cases with abundant fat
The fat-rich submucosa has high electrical resistance, making incision, dissection, and hemostasis
inefficient. In high-voltage and high-modulation mode, such as forced coagulation, it is difficult to dissect
the lesion, and, even worse, there is a lot of fat droplet scattering, which immediately clouds the field of
view. Therefore, it is recommended to use low-voltage and low-modulation modes such as Swift
coagulation and cut modes. On the other hand, hemostasis is reduced in these modes, so it is recommended
to pre-coagulate the vessel using forceps. Because there is little fat directly above the musclaris propria, it is
also important to target this layer for dissection.

Dealing with cases of difficult approach
Scope operability
It is very important to stabilize the scope for colorectal ESD which takes more time than lower endoscopy
and other endoscopic treatments. In colorectal ESD, CO insufflation is essential . When the operability of
[23]
2
the scope is extremely poor, the use of a double-balloon endoscope, a single-balloon sheath, double-balloon
endolumenal intervention platform, or overtube with rigidization feature may be the solution [24-26] .

Use of traction devices
[27]
Since Oyama reported the usefulness of traction devices in gastric ESD in 2002, traction devices have been
evaluated as an adjunct in esophageal and gastric ESD, and various methods have been reported . Because
[28]
of the difficulty in attaching traction device to the colon, it has rarely been performed. In recent years, the
use of traction in the deep colon has been reported , and it has been shown to be effective in cases of both
[29]
difficult dissection and difficult approach [Figure 3].

ESD FOR CHALLENGING COLORECTAL LESIONS
Large lesion
There are occasionally large intramucosal colorectal carcinomas that are indicated for endoscopic
treatment. Although large lesions are often defined as difficult cases because of the longer treatment time ,
[30]
the treatment speed per tumor area tends to be rather fast, if there are no other difficult factors . While
[31]
ESD of these lesions is time consuming, endoscopists often do not find it difficult. However, laparoscopic
surgery for colonic lesions is less invasive and has a better functional outcome. There is no need to insist on
endoscopic treatment at the risk of prolonged treatment, complications, and stricture. However, rectal
surgery is highly invasive and difficult, and it affects the defecation function. Because the rectum has a large
intestinal lumen and a thick musclaris propria, rectal endoscopic treatment is safer than the colon one. In
addition, a large part of the rectum is extraperitoneal, which makes a perforation less dangerous. This is the
area where the benefits of ESD can be best exploited.