What are the recommended step‑by‑step procedural steps for submucosal tunneling endoscopic resection (STER) of a submucosal tumor ≤30 mm located in the esophagus or proximal stomach?

Submucosal Tunneling Endoscopic Resection (STER) Procedural Steps

STER for submucosal tumors ≤30 mm in the esophagus or proximal stomach follows four sequential steps: create a mucosal entry and submucosal tunnel 3–5 cm proximal to the lesion, perform circumferential tumor dissection within the tunnel extending 1–2 cm distal to the lesion, extract the specimen through the tunnel, and close the mucosal entry with endoscopic clips. 1

Pre-Procedural Requirements

Before beginning STER, ensure the patient receives general anesthesia with endotracheal intubation to permit positive-pressure ventilation and control of capnoperitoneum/capnomediastinum. 1

• Use carbon dioxide insufflation exclusively (never air) because CO₂ is rapidly absorbed and carries lower risk of adverse events 1
• Administer prophylactic intravenous antibiotics to reduce infection risk from potential luminal contamination 1
• Have peritoneal decompression needles immediately available to manage intra-procedural pneumoperitoneum 1
• Confirm the lesion is ≤3 cm, as larger tumors are difficult to extract through the tunnel and often require conversion to exposed full-thickness resection 2

Step 1: Mucosal Entry and Tunnel Creation

Create the mucosal incision 3–5 cm proximal to the lesion to allow adequate tunnel length while respecting anatomic constraints. 2, 1

• Inject methylene blue or indigo carmine to locate the tumor precisely before creating the submucosal tunnel 3
• Make the initial mucosal incision between the submucosal and muscular layers 3
• The tunnel provides a confined workspace that improves endoscope stability and supplies natural traction on the lesion during dissection 1
• The overlying mucosal flap limits leakage of luminal contents while the tumor is being dissected 1

Step 2: Submucosal Tunnel Extension and Tumor Dissection

Extend the submucosal tunnel 1–2 cm distal to the lesion to provide a safe working space beyond the tumor margins. 2, 1

• Perform circumferential tumor dissection within the tunnel using endoscopic resection techniques 3
• The confined tunnel space provides both scope stability and traction on the lesion, facilitating complete resection 2
• Dissection within the tunnel minimizes extravasation of luminal contents compared to exposed techniques 2

Step 3: Specimen Extraction

Withdraw the resected specimen through the same submucosal tunnel and mucosal entry point after complete excision. 1

• Lesions larger than 3–4 cm are difficult to extract through the tunnel and usually require conversion to an exposed full-thickness resection 1
• En-bloc resection is achieved in 78.7%–95% of cases, with complete (R0) resection rates ranging from 97.1% to 100% 1

Step 4: Mucosal Entry Closure

Close the mucosal incision with several endoscopic clips to re-establish luminal integrity after specimen removal. 1, 3

• Endoscopic closure of the mucosal flap is generally easier than closing a large defect after an exposed full-thickness resection 1
• The mucosal flap closure restores luminal integrity and prevents contamination 2

Expected Outcomes and Complications

Air-leak complications (pneumothorax, subcutaneous emphysema, pneumomediastinum) occur in approximately 15% of procedures and are usually managed conservatively. 1

• Perforation occurs in about 5.6% of cases, and all reported events have been successfully treated without surgical intervention 1
• Complete resection rate is 100% in experienced hands 4
• Local recurrence or distant metastasis did not occur during follow-up periods ranging from 6-32 months 4

Critical Pitfalls to Avoid

Do not attempt STER for lesions >3–4 cm, as extraction through the tunnel becomes technically prohibitive and conversion to an exposed resection is often required. 1

• Avoid STER in anatomical locations that cannot be reached with a straight-line endoscopic approach (e.g., certain gastric fundus positions), because tunnel creation is extremely challenging 1
• STER should be performed only by endoscopists highly experienced in advanced tissue-resection techniques, such as endoscopic submucosal dissection (ESD) or per-oral endoscopic myotomy (POEM) 1
• The complication rate is significantly higher for lesions originating in the deeper muscularis propria layer (70%) compared to the superficial muscularis propria layer (1.3%) 3