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Page 10 of 20 Nakamura et al. Mini-invasive Surg 2022;6:50 https://dx.doi.org/10.20517/2574-1225.2022.38

Mucosal incision
A partially insulated knife has an insulating tip; therefore, a pre-cut hole must be created at the most distal,
surrounding mucosa with a needle knife. With a partially insulated knife, a mucosal incision is made from a
pre-cut hole on the far side of the lesion to the near side and from the lateral part to the central part. In
contrast, with a needle knife, a mucosal incision is made from the near side of the lesion to the far side and
from the central part to the lateral part.

To reduce the incidence of bleeding during mucosal incision, a shallow mucosal incision is initially made
with the endo-cut mode; then, the incision line is deepened with the coagulation mode (“trimming”),
coagulating the submucosal vessels. This maneuver is particularly useful for lesions located in the corpus,
where many thick vessels often exist in the submucosa. Trimming is often performed up to the plane
between the submucosal vessels and the surface of the muscularis propria. The usefulness of trimming is as
follows: (1) easy recognition of the initial submucosal plane for submucosal dissection; (2) efficient mucosal
lift by submucosal injection to avoid leakage of the injected solution from the well-isolated specimen; and
(3) easy completion of submucosal dissection at the lateral or distal part of the specimen [Figure 6].

An entire circumferential incision is often made before submucosal dissection. However, a specimen is
often shrunk in the center of a small lesion, making the creation of a flap for submucosal dissection difficult.
In this case, a partial (approximately two-thirds) mucosal incision followed by subsequent submucosal
dissection is performed so that the mucosal tension from the opposite side creates a flap, and the remaining
mucosal incision and submucosal dissection are finalized.

Submucosal dissection
After injecting a solution into the deep submucosal plane, submucosal dissection is performed from the
front side of the lesion. With a needle-type knife, submucosal dissection is initiated from the central part of
the submucosa until the lateral edge [Figure 7].

With the partially insulated knife, submucosal dissection is started from the tissue behind the lateral edge of
the submucosa, until it reaches the central part [Figure 8].

Dissection of the lateral edge of the submucosa is important for the efficient creation of a mucosal flap. In
gastric ESD, deep submucosal dissection just above the muscularis propria is important. The vessels in the
gastric wall penetrate the muscularis propria and branch in the submucosa towards the mucosa. As the
branches of the vessels in the shallow submucosa are surrounded by fibrous tissue, dissection of the
superficial submucosa is difficult and may cause hemorrhagic oozing. In contrast, when dissecting the deep
submucosa, although there is a possibility of encountering a thick vessel, there are fewer smaller blood
vessels to encounter, and the submucosa between the vessels is less fibrous than that in the shallow
submucosa [Figure 6D]. Moreover, during deep submucosal dissection, even when the vessels are severed,
the bleeding vessel in the deep submucosa is easily recognized as a vascular stump on the surface of the
muscularis propria, facilitating hemostasis.

Vessel coagulation
It is important to recognize the vessels in the submucosa during ESD for prophylactic coagulation. The vein
appears reddish and is usually accompanied by an artery. The thin artery appears paler than the vein, and
the thick artery appears whitish. The thin vessels are cauterized with an ESD knife using the coagulation
mode. With the Dual knife, the thin vessels are cauterized by a small disk at the tip of the knife with the
knife withdrawn. With the IT knife 2, it is cauterized by a triangle-shaped metal part. With the Flush Knife
BT, the thin vessels are cauterized with the ball tip. IT Forced coagulation with a low high-frequency power