To our knowledge, this is the first study to show the prospective outcomes of h-ESD using a SOUTEN for small gastric tumors. This study demonstrated that h-ESD for small gastric tumors ≤ 15 mm in diameter has favorable outcomes in terms of procedural completion rate, curative resection rate, complication rate, and operative time.
Conventional gastric EMR has a problem of insufficient resection margin owing to slippage of the snare and high local recurrence rate (2,7). The h-ESD method, in which a peripheral incision and dissection similar to that in ESD are performed followed by snaring, allows for a planned and reliable margin. Furthermore, the submucosal layer can be removed in a short time using a snare, which is more time-efficient than conventional ESD (10,11). The h-ESD method can simplify such delicate submucosal dissection procedures, especially for lesions where the knife is perpendicular to the mucosa, which tends to be difficult to perform with conventional ESD owing to the high risk of perforation.
A retrospective comparison of 29 cases of h-ESD had a median procedure time of 20 minutes, compared with 40 minutes for the conventional method, indicating that h-ESD can be performed in a shorter time . Although the study showed favorable outcomes with a 100% en bloc resection rate, there were issues in terms of possible bias in the selection of lesions that were easily performed for h-ESD and sample size. In this study, we conducted a prospective observational study with a larger number of consecutive cases according to the inclusion/exclusion criteria to further validate the points to be considered in the application of h-ESD.
In this study, h-ESD for small gastric tumors using a SOUTEN showed a satisfactory completion rate of 91.2% and curative resection rate of 94.7%. The average procedure time was 21.2 minutes. No perforation or intraoperative hemorrhage was observed, and postoperative hemorrhage occurred in 1.8% of cases, indicating that h-ESD has acceptable safety.
The SOUTEN can perform two roles; it can be used as a needle scalpel for incision and dissection of the peripheral area when it is retracted and as a snare for snaring and resection of lesions when it is expanded. The tip of the device has a knob-like shape that allows it to be used as a hook for cutting. The protruding length of the device may change as the endoscope moves; therefore, it is necessary to pay attention to the changes. The price of a SOUTEN is approximately 8,000 yen, which is roughly one-third the price of conventional ESD devices (20,000–40,000 yen), making it a device with excellent medical economic benefits.
Currently, h-ESD is already being introduced and widely used for colorectal tumors, where its efficacy has been demonstrated (8,12,13). A recent meta-analysis comparing conventional ESD and h-ESD for colorectal tumors showed significantly shorter procedure times (mean difference 18.45 min; P = 0.003) and lower complication rates but lower en bloc resection rates (P < 0.001) for h-ESD (13). This suggests that it is important to determine the indications for h-ESD in the stomach to increase the en bloc resection rate and to improve the technique. The appropriate lesion diameter for h-ESD with a SOUTEN is ≤ 15 mm in diameter, with an expected margin of 5 mm around the lesion, and a maximum resection area of 25 mm in diameter. The SOUTEN snare width is 15 or 20 mm, and when pressed against the mucosa, it expands to a circular shape approximately 30 mm in diameter. By sufficiently dissecting the surrounding area, the lesion size can be reduced to a smaller size and fit within the snare. The snare may not fit properly in narrow spaces, such as the cardia and pylorus, making it difficult to apply. In addition, because the submucosa cannot be seen during snaring, it is not indicated in cases where SM invasion or fibrosis of the submucosa is suspected, and it was excluded from this study.
Of the 57 cases reviewed in this study, h-ESD was discontinued in three cases and converted to conventional ESD. In all cases, the lesion diameter was approximately 15 mm in diameter, which is the limit of the indication, and the lesion did not fit into the snare at the stage of snaring after circumferential incision, resulting in prompt transition to ESD and curative resection. In this case, the SOUTEN alone was sufficient to complete the ESD and could be used as an ESD device. As described above, the h-ESD method using SOUTEN can be used to achieve a reliable en bloc resection by shifting to ESD flexibly according to the lesion site and size.
Of the 57 cases, one had a positive horizontal margin, and two had an X horizontal margin. The positive horizontal margin was caused by errors in range diagnosis, and there were no problems with the h-ESD technique. In the two cases with a horizontal X edge, the burning effect of the circumferential incision affected the edge, resulting in an unknown margin. There were no residual lesions or recurrence in the follow-up. The problem is that h-ESD tends to have a narrow surgical margin because the difficulty of snaring increases as the resection area increases. As a result, a burning effect is caused in the lesion, making it difficult to evaluate horizontal margins. Therefore, h-ESD should be applied only to small lesions ≤ 15 mm with an appropriate margin of at least 5 mm around the lesion; if snaring is judged to be difficult, it is important to switch to conventional ESD.
In two cases, tissue was left behind at the margins after snaring resection. The remnant tissue was healthy mucosa at the margins, and although the lesions themselves were resected en bloc, this is an event that requires attention. In both cases, the remnant tissue was on the distal side of the scope, and it was thought to be caused by the difficulties with visibility during snaring. To prevent this, it is important to dissect the distal side sufficiently before snaring. It is also important to set an appropriate margin in case residual tissue is left behind.
In addition to the SOUTEN, additional devices were required in only two out of 57 cases, and it was possible to complete the procedure using the SOUTEN alone in most cases, thus realizing a low-cost treatment. Both cases were lesions in the U region. One of the cases was a bleeding lesion in the upper gastric lessor curvature, and an IT knife 2 (KD-611L, Olympus, Tokyo, Japan) was additionally used as an incision scalpel with high hemostatic capacity during full circumferential incision. In another case, the lesion was in the fornix and the risk of perforation using the SOUTEN tip knife was high owing to respiratory variability, therefore an IT knife 2 was used for full circumferential incision. The submucosal dissection of the fornix was difficult to perform, and as a result, h-ESD was able to reduce the difficulty relative to that with conventional ESD.
Some of the limitations of this study are listed below. This was an observational study with a single arm. A prospective randomized control trial is needed to establish h-ESD using a SOUTEN as a standard procedure. In order to ensure a certain level of safety, ESD trainees were excluded. Although h-ESD is not more difficult than conventional ESD because it can greatly shorten the process of submucosal dissection, whether h-ESD can be performed safely and efficiently by beginners needs to be examined in the future.