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

together. Submucosal tissue is dissected including the area around the deep appendix and final incision of
the appendiceal mucosa is made from the submucosal side (Strategy B). Although Strategy B requires
significantly longer treatment time, the cases of postoperative appendicitis are rare and can be managed
[38]
conservatively . It is less invasive than ileocecal resection. However, the risk of incomplete resection is high
if the target lesion reaches and enters the appendiceal orifice to the extent that the tumor edge cannot be
seen when looking into the appendiceal lumen without appendectomy.

Lesions involving the ileocecal valve
First, it is important to confirm that the endoscope can reach the oral side of the lesion. If the endoscope
can reach the lesion, even lesions involving the terminal ileum can be resected. Incision of the mucosa and
vascular network on the ileal side should be performed first to prevent the lesion from shifting to the ileal
side. The musclaris propria in this area is bent, and the muscle fiber bundles are thin, sparse, and light in
color, so it must be carefully separated from the submucosa. Compared with cecal lesions, the time and
speed of the procedure are significantly inferior, but the en bloc resection rate is not different. Interestingly,
there were no stenosis symptoms in all cases reported, including those with over 95% of mucosal defects of
[39]
circumference . It was reported that no stenosis occurred even after a full circumferential resection, and
we believe that stenosis does not occur unless ESD is performed deep into the ileum [Figure 5].

Large, protruded lesion and muscle retracting sign
In a recent analysis of factors associated with difficult colorectal ESD , a large, protruded lesion is
[40]
recognized as one of the difficult cases. The depth of protruded lesions larger than 3 cm cannot be
accurately diagnosed even with ultrasound endoscopy, enterography, and magnifying endoscopy. Some of
these lesions may be intramucosal carcinoma or adenoma, but some have muscle retracting sign (MR sign),
where the muscle layer is pulled towards the lesion, and the dissection may be very difficult and
[41]
dangerous . Most of them are due to desmoplastic reactions associated with deep submucosal invasion,
[41]
but about 30% of the lesions with MR sign are intramucosal lesions or slight submucosal carcinoma . In
addition, deep submucosal carcinoma has a very low rate of metastasis in the absence of risk factors other
than deep invasion , and expanded indications for these lesions are being discussed.
[42]

Pocket-creation method and per anal endoscopic myectomy
The development of the pocket creation method (PCM) has been a major advance in ESD in recent
years . When conventional ESD using a mucosal flap is performed in cases with MR sign, the MR area
[43]
becomes unstable, and the field of view becomes poor. PCM allows traction against the musclaris propria by
diving into the submucosa through a minimal mucosal incision and suspending the submucosa with the
lesion and surrounding mucosa. If opening the sides of the pocket is difficult, a traction method called
retroflex traction technique can be useful. With this traction technique, the endoscope is passed through the
pocket and retroflexion is performed. The lesion is lifted by the endoscope, and good counter traction
makes it easy to open the sides of the pocket. In addition, we also developed per anal endoscopic myectomy
(PAEM) by applying peroral endoscopic myotomy, submucosal endoscopic tumor resection, and the pocket
[44]
method . In PAEM, the submucosa on both sides of the severe fibrosis with MR sign is first dissected using
double tunneling, and the circular muscle around the fibrosis is incised. Subsequently, the space between
the circular muscle and the longitudinal muscle is dissected, and the lesion and the circular muscle is
resected together. Although PAEM is limited to rectal cases, it can be applied to the treatment of
anastomotic lesions and residual recurrence after transanal endoscopic microsurgery.

Supplementary Video 1 demonstrated an effective retroflex traction technique procedure for opening the
side of a pocket in the pocket creation method.