Resection depth: a very important advantage for underwater EMR.

This paper compared the histopathological results of consecutive cases of 6- to 9-mm definite benign tumors resected by cold snare polypectomy (CSP), hot snare polypectomy (HSP), or underwater endoscopic mucosal resection (UEMR) by two endoscopists at one institution. The authors assessed whether the specimens contained muscularis mucosa (MM) and submucosal (SM) tissues and measured the thickness from the MM to the vertical resection margin of SM tissue at the center of the resected specimens.

Although this was a retrospective study with limitations, such as the lack of tissue stretching, the results are significant in that they show the superiority of UEMR 1 2 in that the MM to SM layer can be sufficiently resected compared to CSP and HSP.

The results of this study suggest that UEMR should be the treatment of choice for patients with suspected cancer (high-grade dysplasia in Western Europe), i. e., JNET 3 4 5 type 2B or Pit pattern type V lesions 6 , rather than CSP or HSP.

The question that arises is whether UEMR can provide the same SM layer as conventional EMR with saline injection into the SM layer. Although the authors excluded EMR from their study because EMR, unlike other resection methods, requires local injection, what is of real interest is the comparison between UEMR and EMR when treating early cancers.

Recent meta-analyses 7 8 and one randomized controlled trial (RCT) 9 have demonstrated both the superior efficacy of UEMR over CEMR regarding R0 resection rate for colorectal polyps and shorter resection time. However, few published RCTs have evaluated whether there is an advantage to using UEMR over CEMR for colorectal polyps ≥ 20 mm in diameter, when en bloc CEMR would be difficult. The result from the RCT by Nagl et al 1 , comparing UEMR with CEMR for colorectal polyps larger than 20 mm in diameter, is highly significant. The secondary outcomes of en bloc and R0 resection rates were both higher in UEMR compared with CEMR, which demonstrated the technical superiority of UEMR compared with CEMR. One of the limitations observed was that the higher en bloc and R0 resection rates for UEMR compared with CEMR were driven mainly by the subgroup of polyps with diameters of ≥ 20 to ≤ 30 mm in size, and such results were limited to this size range.

Recently, Takeuchi et al. published a review on UEMR 10 . According to their review, UEMR is recommended for lesions < 2 cm in size due to its en bloc resection rate and lower complication, however, further study will be needed for lesions > 2 cm because of the limited data from only one single-center RCT.

Early-stage cancers > 20 mm in diameter, which are usually difficult to resect en bloc by conventional EMR, must be resected en bloc by endoscopic submucosal dissection (ESD) 11 12 .

There is concern that ESD may result in a thinner SM layer compared to EMR. Unfortunately, many of the lesions amenable to ESD are difficult to resect en bloc with EMR, making comparative studies between the two difficult to perform 13 .

However, the advantage of ESD is that the depth of dissection can be adjusted.

Therefore, when ESD is performed by an expert, the submucosal layer can be opened firmly with a short type ST hood 14 , and cutting line can be targeted above the muscular layer to ensure diagnostic treatment of lesions that are clinically suspected to be T1.

We currently choose an additional SM injection even with underwater conditions when we suspect cancer, including intramucosal disease. This is because we want to ensure a sufficiently deep margin for cancer treatment.

One of the reasons for recommending UEMR over CEMR is that it is difficult to achieve proper SM injection with CEMR. In this regard, the SM layer is expanded with underwater conditions, which may facilitate proper SM injection.

In fact, when a lesion is injected underwater, the SM layer is further raised sufficiently, and snaring underneath the SM provides a sufficient margin. Despite the labor and cost of SM injection, it may be a good technique for lesions that are suspicious for cancer.

Although the evidence is not high in these expert limited cases compared to RCTs, we would like to have more data on the depth of resection between UEMR and underwater and inject EMR in the future. Also, it may be necessary to collect data about UEMR on the depth of resection according to the tumor gross type, as non-polypoid-type lesions often has poor SM lifting.

Conclusions

In summary, the authors found that UEMR is superior to CSP and HSP in terms of depth of resection. However, whether UEMR is sufficient for lesions suspected of being cancer will require comparative data with underwater and inject EMR.