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Page 2 of 8 Hayashi et al. Mini-invasive Surg 2022;6:7 https://dx.doi.org/10.20517/2574-1225.2021.125

indicated for superficial gastrointestinal tumors. Some submucosal invasive cancers have a risk for lymph
node metastases. Endoscopic treatment can achieve local tumor resection without the eradication of
regional lymph nodes. However, the risk can be predicted through pathological examination of resected
specimens because the risk factors are present in the submucosa of the specimens. Therefore, when
endoscopically resecting the tumors not only an R0 resection, which means resection of a specimen
including the whole tumor with a negative margin, but also the less-damaged thick submucosa of the
specimen is required to predict the risk of lymph node metastases.

Endoscopic submucosal dissection (ESD) is one type of endoscopic treatment that is becoming the standard
treatment for superficial gastrointestinal tumors in the case of lesions especially challenging for
conventional endoscopic resection (e.g., endoscopic polypectomy, endoscopic mucosal resection, etc.)
because ESD can achieve an R0 resection with sufficient submucosa. However, ESD is still technically
challenging for many endoscopists who have not had sufficient experience with the procedure. There are
several factors for these difficulties. For instance, endoscopic maneuverability, thickness of the muscularis,
the presence of blood vessels, degree of submucosal fibrosis, and fluctuations due to breathing and heartbeat
differ in each organ, and even at each location within the organs.

Recently, the pocket-creation method (PCM) was developed to standardize the strategy of ESD. Efficacy of
[1-8]
PCM was revealed not only in the colorectum but also in upper gastrointestinal tract .
The pocket-creation method
PCM was originally developed to completely resect colorectal sub-pedunculated tumors with severe
submucosal fibrosis . Formerly, we performed ESD using the conventional strategy in which a mucosal
[1]
incision was made for at least one-quarter of the circumference and submucosal dissection below the
[5]
incised area were made alternatively . However, when dissecting a tumor with severe submucosal fibrosis
using the conventional strategy, it can be too difficult to identify and resect the fibrotic submucosa between
the tumor and muscularis because the injected solution can leak out of the wide mucosal incision and the
tip of the endoscope can be unstable in the opened submucosal space. Meanwhile, PCM with a small initial
mucosal incision minimizes leakage of the injected solution and makes the endoscope tip stable in the
submucosal pocket [Figure 1]. In addition, a conical transparent cap , small-caliber-tip transparent (ST)
[9]
hood (DH-33GR, DH-34CR, Fujifilm, Tokyo, Japan) naturally produces both traction and countertraction
to stretch the fibrotic submucosa in the limited-space pocket, which facilitates cutting the submucosa. It is
like stretching cloth when cutting it with scissors. Although PCM was initially developed to overcome
challenging sessile colorectal tumors, it has been found to be useful in dissecting ordinary flat tumors such
as laterally spreading tumors . PCM has been the standard strategy for colorectal ESD, especially in our
[2,5]
institution for a long time.

Devices for PCM
The ST hood is a key device for performing PCM. The ST hood facilitates entry of the tip of the endoscope
to the submucosal layer quickly and produces traction from the center to the outside in the endoscopic
view. A guide rail prepared inside the ST hood can also move the tip of the endoscopic device to the center
of the endoscopic view. A needle-type knife such as Flushknife (Fujifilm) or Dualknife (Olympus, Tokyo,
Japan) is appropriate for PCM because the centered tip of the needle-type knife cuts submucosal tissue in
any direction. Injecting a viscous solution, such as 0.4% sodium hyaluronate, prolongs thickening of the
submucosa which also facilitates PCM .
[9]