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Kato et al. Mini-invasive Surg 2022;6:10 https://dx.doi.org/10.20517/2574-1225.2021.124 Page 3 of 8

KNACK AND PITFALL
ESD of the duodenum is technically more difficult compared to other organs because of various anatomical
features. The endoscope maneuverability is impaired because of the distance from the oral cavity and fixed
position to the retroperitoneum of duodenum. It is often difficult to approach the lesion tangentially, and
only the perpendicular approach is possible, especially in the flexural position of the duodenum (e.g.,
superior and inferior duodenal angles). The wall of the duodenum is so thin that the outer structure can
sometimes be seen through it; therefore, only a small inadvertent cauterization, even hemostasis, towards
the muscle layer can easily cause perforation. The submucosal layer to dissect is very narrow because of rich
Brunner’s glands especially in proximal duodenum. There are rich blood vessels in the submucosal layer,
and even a thin blood vessel could cause massive bleeding. In addition, only a tiny biopsy before ESD often
causes severe fibrosis of the submucosal layer, which makes endoscopic resection difficult . In fact, a
[29]
[23]
recent multi-center retrospective study has demonstrated an intraprocedural perforation rate of 9.3% . In
that study, this high incidence was observed even though all participating institutes were high-volume
Japanese centers; thus, duodenal ESD is still challenging even for highly experienced endoscopists.

The first step to overcome the abovementioned difficulties is to understand predictors for technical
difficulties. We explored predictors for intraoperative perforation and the procedure requiring a long time;
these were set as surrogate endpoints for technical difficulties. We found lesions located in the flexural part
such as the superior or inferior duodenal angle, large lesion size, and occupied circumference of the lesion
exceeding half the circumference were independently associated with technical difficulty . Knowledge of
[30]
these predictors is expected to be useful when preparing for difficult duodenal ESD, for example by
planning a procedure under general anesthesia.

TECHNIQUE
Although duodenal ESD is difficult, several modified techniques and recently developed devices have been
proposed. Improvement of visualization of the submucosa is one of the most important keys to safe and
successful ESD.

We invented the water pressure method (WPM), in which active water flow is utilized by the water jet
[31]
function of a therapeutic endoscope . First, the lumen of the duodenum is filled with normal saline, and,
just after the mucosal incision, the active water stream is aimed at the mucosal flap to open the tissue
[Figure 1]. Generally, it is very difficult to dissect the submucosal layer at the beginning of submucosal
dissection because it is impossible to directly visualize the dissecting layer due to the narrow space. WPM
enables direct observation of the submucosa even at the very early stage of submucosal dissection by
exposure of the tissue using an active water stream. Another advantage of WPM is that it makes it easier to
dissect the lateral edge of the lesion. It is also relatively difficult to dissect this area because of the narrow
space, and WPM assists by opening the space using active water pressure. Actually, we reported that WPM
significantly reduces perforation during the ESD procedure as well as significantly shortens the procedure
time .
[27]

[22]
Miura et al. reported the effectiveness of the pocket creation method (PCM). In PCM, a small, tapered tip
hood is used to create a pocket by dissecting the submucosa without a circumferential incision. PCM
contributes to stabilizing the endoscope and improving the visibility of the submucosal layer. Moreover,
there is a report addressing the effectiveness of a traction device . These newly reported modified ESD
[32]
techniques are expected to improve duodenal ESD.