The Pocket-Creation Procedure of Endoscopic Submucosal Dissection for Large Rectal Laterally Spreading Tumors

Colorectal cancer (CRC) remains a leading cause of cancer-related morbidity and mortality worldwide^1,2,3. Early detection and minimally invasive removal of precancerous lesions are pivotal for CRC prevention. Among these, laterally spreading tumors (LSTs) - characterized by their horizontal growth pattern along the mucosal surface rather than vertical protrusion - constitute a clinically significant subset. Histological studies confirm that LSTs exceeding 20-30 mm exhibit substantially higher rates of submucosal invasion compared to conventional polyps^4,5.

En bloc R0 resection is critical for large LSTs to enable precise pathological staging and reduce recurrence⁶. While EMR effectively treats small lesions (<20 mm), extensive LSTs require Piecemeal endoscopic mucosal resection (pEMR) due to technical constraints. This fragmented approach impedes accurate histological margin assessment, elevating risks of incomplete resection and local recurrence^7,8,9,10.

To address these limitations, endoscopic submucosal dissection (ESD) has emerged as the preferred technique for achieving en bloc resection of large non-invasive colorectal neoplasms, including LSTs^11,12. However, colorectal ESD is technically complex with a steep learning curve. The inherent thinness of the colorectal wall, particularly in the right colon and rectum, coupled with the tortuous and confined lumen, significantly increases the risk of perforation and prolongs procedure time, limiting its widespread adoption and posing safety concerns even in experienced hands^13,14,15.

The Pocket Creation Method (PCM) -ESD represents a specialized ESD technique for optimizing the lumen of the stomach or colon^16,17,18. Unlike tunneling approaches (e.g., Endoscopic submucosal tunnel dissection, ESTD), PCM-ESD involves creating a small mucosal incision to access the submucosal space. The endoscope is then inserted into this initial opening to dissect the entire submucosal plane beneath the lesion before circumferential mucosal incision¹⁹. This "blind pocket" architecture maintains the mucosal flap's integrity, providing crucial counter-traction throughout the dissection. This "blind pocket" architecture maintains the mucosal flap's integrity, providing crucial counter-traction throughout the dissection²⁰. Comparative studies demonstrate that PCM-ESD significantly improves R0 resection rates (93.5% vs. 78.1%), accelerates dissection speed, and reduces adverse events relative to conventional ESD, offering advantages when dedicated traction devices are unavailable^21,22.

By enhancing scope stability and submucosal visualization while preserving a durable fluid cushion, PCM-ESD directly addresses the anatomical constraints of the colon and rectum. This technique facilitates safer and more efficient en bloc resection of challenging LSTs, overcoming key limitations of conventional ESD in this setting.

The protocol was approved by the Institutional Review Board of the First Affiliated Hospital of Jinan University. The study included three patients who underwent PCM-ESD between August 2024 and July 2025. All procedures were performed in accordance with institutionally approved protocols after obtaining written informed consent from the patients. The materials and equipment used are listed in the Table of Materials.

1. Preoperative preparation

1. Obtain written informed consent from all patients after explaining the risks of perforation, bleeding, and possible conversion to surgery.
2. Perform endoscopic ultrasound (EUS), enhanced computed tomography (CT), or magnetic resonance imaging (MRI) to exclude deep submucosal invasion (>1000 µm).
3. Draw venous blood for complete blood count and coagulation parameters, including prothrombin time/INR and activated partial thromboplastin time (aPTT).
4. Administer bowel preparation using 3L polyethylene glycol solution split over 12 h pre-procedure. Confirm clear effluent (Boston Bowel Preparation Scale ≥8).
   NOTE: Terminate the procedure if muscularis propria invasion is detected during preoperative assessment.

2. Preoperative workup

1. Endoscopic system preparation
   1. Mount the transparent cap onto the distal tip of the GIF-H260J endoscope.
   2. Connect the CO₂ insufflation tubing to the regulator port on the endoscope control unit.
2. Submucosal injection solution preparation
   1. Add 6 mL of 0.2% indigo, carmine mucosal dye to 250 mL of normal saline to prepare the submucosal injection solution. Mix thoroughly before use.
3. Electrocoagulation
   1. Configure the VIO 300D generator by sequentially activating Endocut Q mode with parameters set to Effect 3, Duration 2, and Interval 4 for precise mucosal incision, then immediately engage FORCED COAG mode at Effect 3 and 50W output for submucosal dissection.
   2. For active hemorrhage control, use a single-use high-frequency knife through the accessory channel. Set the generator to SOFT COAG mode (Effect 6, 80W) for immediate bleeding control. Apply precise tangential coagulation to bleeding vessels for 1-2 s.

3. PCM-ESD procedural steps

1. Mark lesion boundaries.
   1. Delineate the lesion border using either of the following methods:
      1. Electronic chromoendoscopy: Switch the endoscope to Narrow Band Imaging (NBI) mode to enhance the visual contrast between the lesion and the surrounding normal mucosa.
      2. Dye-based chromoendoscopy: Spray 0.2% indigo carmine solution onto the mucosa to dye the lesion and clearly delineate its border.
   2. Using the single-use high-frequency ESD knife, place coagulation marks exactly 0.5 cm outside the stained lesion edge. Apply the marks with a 2 mm spacing using the tip of the ESD knife in FORCED COAG mode (Effect 2, 20 W).
2. Perform initial submucosal injection.
   1. Inject the indigo carmine-saline solution immediately outside the planned resection margin to create a sustained fluid cushion.
3. Establish tunnel entry.
   1. Select the anal-side marking point as the entry site.
   2. Make an arc-shaped incision at the anorectal margin of the lesion using a disposable mucosal knife to create a mucosal flap and establish the tunnel entry point.
      NOTE: Attention should be paid to applying appropriate force to press the knife against the mucosal surface during the incision, ensuring that the mucosa/mucosal muscle layer is cut through in one stroke until a small part of the submucosa is incised. See Figure 1.
4. Create submucosal tunnel. See Figure 2.
   1. Advance the endoscope into the submucosal space.
   2. Dissect submucosal fibers horizontally using ESD knife (FORCED COAG mode).
   3. Maintain dissection plane immediately above the muscularis propria to avoid the more vascular superficial submucosa.
      NOTE: Pay attention to injecting air while dissecting to maintain a clear dissection field and identify the appropriate depth and angle for dissection. Identify and preserve perpendicular vessels >1 mm diameter.
5. Extend the submucosal tunnel to the oral side.
   1. Continue dissecting from the submucosal pocket toward the oral side until the tunnel beyond the oral tumor margin.
   2. Inject additional indigo-carmine-saline solution as needed to maintain lift.
   3. Complete the submucosal incision on the oral side to clearly define the resection endpoint and achieve full communication between the anal-side and oral-side tunnels.
      NOTE: For any intraprocedural bleeding, coagulate immediately using the ESD knife or hemostatic forceps.
6. Complete the lateral mucosal incisions.
   1. Under direct vision, incise the mucosa along the pre-marked margin on the gravity-dependent side first, then proceed to the non-gravity side, advancing stepwise until the entire lesion is circumferentially freed. See Figure 3 and Figure 4.
   2. Throughout the dissection, pre-coagulate any visible vessels with the ESD knife in SOFT COAG mode, maintaining continuous visualization and ensuring the muscularis propria remains intact.
      NOTE: Take care to keep the specimen attached at one edge until the final moment to provide counter-traction.
7. Retrieve the specimen and manage the post-resection wound.
   1. Engage the freed lesion with a snare or apply continuous endoscopic suction to extract the intact specimen en bloc.
   2. Inspect the post-resection bed; identify every visible vessel and thermally coagulate it with hemostatic forceps or the ESD knife set to SOFT COAG mode to prevent delayed bleeding. See Figure 5.
      NOTE: If perforation is encountered, close it with clips as soon as feasible, ideally after securing an adequate dissection plane.
8. Specimen handling
   1. Gently irrigate the specimen with saline to remove debris.
   2. Pin the specimen flat, mucosal side up, on a corkboard using fine needles at 2-3 mm intervals.
   3. Immerse in 10% buffered formalin for at least 12 h.
9. Post-operative care
   1. Monitor vital signs and assess for abdominal pain, hematemesis, melena, or rising pulse.
   2. Initiate liquid diet at 6 h if there is no abdominal tenderness.

This study successfully applied the Pocket Creation Method (PCM-ESD) in three consecutive patients with large rectal LSTs (4.2-7 cm), two of whom involved the anal line. All procedures were performed by dedicated therapeutic endoscopists, each with more than 3 years of independent ESD experience following formal training. Key demographic and clinical characteristics are detailed in Table 1. The cohort comprised one male and two females aged 57-87 years, including an 87-year-old male with an infrarenal abdominal aortic aneurysm (non-anticoagulated) and a hypertensive patient managed with cilnidipine. Preoperative evaluation revealed mild-to-moderate anaemia in two patients (haemoglobin 87 g/L and 122 g/L); electrolytes, liver and renal function, and coagulation parameters were otherwise normal. CT imaging showed only rectal wall thickening without a mass effect. All procedures were completed under general anesthesia with endotracheal intubation, with no conversions to open surgery.

Critical technical outcomes demonstrated that en bloc resection was achieved in 100% (3/3) of lesions, with R0 margins histologically confirmed in all specimens. The mean dissection speed was 0.414 ± 0.199 cm²/min, which was approximately 20% faster than the historical average for conventional ESD (0.345 ± 0.222 cm²/min) performed by proficient operators at our center for large rectal LSTs >3 cm. None of the three procedures resulted in intra-operative perforation; one patient experienced self-limiting hematochezia on post-operative day 2 that required neither transfusion nor endoscopic haemostasis and was managed conservatively with fluid resuscitation. All patients resumed oral intake within 24 h, and the mean post-operative hospital stay was 5 ± 2 days.

Histopathological examination revealed high-grade intraepithelial neoplasia in all specimens, including sessile serrated adenoma, serrated adenoma, and tubular adenoma. Despite the limited sample size, PCM-ESD demonstrated a favorable dissection speed and safety profile, even in elderly patients with significant comorbidities.

Figure 1: Mucosal incision. An arc-shaped incision of the mucosa is made at the anorectal margin of the rectal LST lesion using a disposable mucosal knife to create a mucosal flap and establish the entry point for the submucosal tunnel. Please click here to view a larger version of this figure.

Figure 2: Submucosal dissection. Utilize the traction force of the submucosa to perform efficient dissection in cutting mode. During the dissection process, continuous air injection is used to adjust the distance from the submucosal layer. Please click here to view a larger version of this figure.

Figure 3: Incising the gravity-side mucosa. The gravity-side mucosa is fully trimmed and dissected while preserving the mucosa on the non-gravity side, and the dissection is advanced towards the non-gravity side. Please click here to view a larger version of this figure.

Figure 4: Incising the non-gravity-side mucosa. A localized injection is administered on the non-gravity side to establish a fluid cushion. The mucosa is then incised, and the lesion is progressively and completely dissected. Please click here to view a larger version of this figure.

Figure 5: Managing the post-resection wound. After the lesion is completely resected, inspect the post-resection wound; identify each visible vessel and thermally coagulate it with a hemostatic forceps or an ESD knife to prevent delayed bleeding. Please click here to view a larger version of this figure.

Table 1: Patient characteristics and outcomes.

The successful implementation of the Pocket-Creation Method for ESD (PCM-ESD) in resecting large rectal LSTs hinges on several critical steps within the protocol. First, the precise creation of the tunnel entry point via an arc-shaped incision at the anal side is paramount. This initial step must cleanly incise the mucosa and a portion of the submucosa to allow smooth scope insertion without damaging the underlying muscularis propria²³. Second, maintaining a durable fluid cushion and a clear visual field throughout submucosal tunneling is essential. Continuous air insufflation and judicious re-injection of dyed saline help preserve the dissection plane and identify submucosal vasculature²⁴. Third, the sequential incision of the gravity-side mucosa first, followed by the non-gravity side, leverages the specimen's own weight for counter-traction, which is a fundamental advantage of this method and facilitates a safer and more efficient dissection²³.

Despite the standardized protocol, certain scenarios may require technical modifications and troubleshooting. In cases of severe fibrosis, this may hinder the advancement of submucosal tunnels. The use of a scissors-type knife for grasping during dissection or clip traction can enhance exposure and reduce perforation risk^25,26.

For active bleeding that obscures the visual field within the pocket, immediately use the ESD knife in SOFT COAG mode or introduce hemostatic forceps for targeted coagulation. If the fluid cushion dissipates rapidly, injecting higher-viscosity solutions such as hydroxypropyl methylcellulose or 0.4% sodium hyaluronate can provide a longer-lasting lift, though their injection through knife channels may be more challenging²⁷. Furthermore, if the lesion is located near the dentate line, careful retroflexion and adjustment of the patient's position are crucial to optimize the approach angle.

PCM-ESD differs from ESTD in that the former creates a blind tunnel with no distal opening, whereas the latter has two openings. The clinical benefits of PCM-ESD for large rectal LSTs are threefold²⁸. First, the pocket-creation strategy markedly improves procedural efficiency, achieving a mean dissection speed of 0.414 cm²/min -- 20% faster than conventional ESD. Second, it enables radical yet conservative resection, attaining R0 resection in 100% of cases, even in challenging locations adjacent to the dentate line, while preserving sphincter function and avoiding surgical conversion and its associated complications such as permanent stoma, anastomotic leakage, and temporary or permanent colostomy. Third, PCM-ESD is safe; even high-risk patients, such as an 87-year-old with an aortic aneurysm, experience few intra- or post-operative complications. This safety profile is attributed to the excellent operative field and visualization provided by intrinsic mucosal traction, as well as proactive coagulation of large vessels, which minimizes intra-operative and delayed post-operative bleeding²⁹.

This study further validates the efficacy and safety of PCM-ESD for complex rectal lesions. When performed by experienced operators at our center, PCM-ESD achieved a resection speed approximately 20% faster than conventional ESD (0.41 vs. 0.345 cm²/min). Successful R0 resection was accomplished in all high-risk patients, with only a single case of self-limiting hematochezia that required no intervention, confirming its favorable safety profile. These findings align with a Japanese systematic review and meta-analysis, which reported superior R0 resection rates, faster dissection speed, and lower perforation rates with the PCM approach²⁰. These outcomes demonstrate that PCM-ESD remains a viable, minimally invasive option even under complex conditions, enabling sphincter-preserving radical resection where conventional ESD or surgery may pose higher risks, thereby aligning with the goals of precision oncology by avoiding extensive surgery, shortening hospital stays, and improving quality of life. Although ESD remains the standard of care, PCM-ESD presents a compelling alternative for large lesions (>4 cm) given its lower risks of bleeding and conversion. However, the limited sample size of this study warrants further validation in larger cohorts, particularly for lesions with deep submucosal invasion. PCM-ESD offers a minimally invasive option that avoids surgical complications while enabling radical resection of challenging rectal lesions. Although ESD remains the current standard, its high bleeding and conversion rates for large lesions (>4 cm) support PCM-ESD as a superior alternative.

In summary, the future applications of PCM-ESD are promising. The technique is adaptable for use in other anatomical locations, such as the duodenum or anastomotic sites, where stable scope positioning is challenging. Integration with emerging technologies like artificial intelligence for real-time dissection plane recognition and the development of dedicated, curved-tip tunnel knives could further standardize the procedure and shorten the learning curve. Furthermore, the principles of PCM-ESD align perfectly with the goals of precision endoscopic surgery, offering a sphincter-preserving, minimally invasive therapeutic option for an expanding range of complex gastrointestinal neoplasms. As expertise grows, PCM-ESD has the potential to become the first-line endoscopic treatment for large, complex rectal lesions, reducing the need for radical surgery and improving patients' quality of life.