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

Summary

This study details a standardized PCM-ESD protocol for resecting large rectal LSTs, aiming to enhance dissection speed and prevent transmural perforation via submucosal tunneling.

Abstract

This study introduces in detail a standardized Pocket Creation Method (PCM) of endoscopic submucosal dissection (ESD) protocol for the resection of large laterally spreading tumors (LST) of the rectum, aiming to overcome the limitations of traditional ESD by improving safety and dissection speed. The procedure is as follows: First, after marking the boundaries, a submucosal injection of indigo carmine-saline solution is administered to achieve sufficient lesion elevation. A disposable mucosal knife is then used to create an arc-shaped incision at the anorectal edge of the lesion, establishing the entry point for the submucosal tunnel. The tunnel is advanced orally along the plane between the submucosa and the muscularis propria, while maintaining the submucosal injection to ensure clear dissection layers. As the tunnel approaches the oral margin of the lesion, the scope is reversed to observe and complete the oral submucosal incision, determining the endpoint of dissection and achieving tunnel continuity from the anal to the oral side. Finally, the mucosal edges on the gravity and anti-gravity sides are cut sequentially to completely resect the lesion. During the surgery, vessels are pre-coagulated under direct visualization to avoid injury to the muscularis propria. Meanwhile, the retention of submucosal injection fluid enhances the "fluid cushion" effect, improving dissection speed and safety, and shortening the surgical time. By optimizing the tunnel vision and effectively maintaining the fluid cushion, this protocol overcomes the limitations of traditional ESD, enabling efficient, safe, and radical resection of large rectal LSTs, while avoiding the trauma associated with surgical resection. This technique offers an effective therapeutic strategy for the treatment of complex rectal lesions.

Introduction

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.

Protocol

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.

Results

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 ab...

Discussion

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 cl...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Electrocoagulation	VIO 300D	erbe	An electrosurgical generator for tissue cutting and hemostasis
Endoscope	Olympus	GIF-H260J	A high-definition gastroscope for endoscopic procedure
Indigo carmine mucosal dye	MICRO-TECH	MTN-DYZ-15	Mucosal contrast enhancement submucosal injection
Single-use high-frequency knife	Olympus or MICRO-TECH	KD0655Q or MK-T-1-195	A disposable electrosurgical device enabling precise mucosal incision and submucosal dissection
Transparent cap	Olympus	D-201-11804	A distal attachment mounted on the endoscope tip