Steps of Submucosal Tunneling Endoscopic Resection (STER)
STER involves four sequential steps: (1) creating a mucosal entry point and submucosal tunnel 3-5 cm proximal to the lesion, (2) dissecting the tumor within the tunnel space, (3) extracting the resected specimen through the tunnel, and (4) closing the mucosal entry site with endoscopic clips. 1
Step 1: Tunnel Creation and Entry
Mark the lesion location by injecting methylene blue or indigo carmine to clearly identify the tumor boundaries 2
Create a longitudinal mucosal incision approximately 3-5 cm proximal to the lesion (as feasible based on anatomy) 1, 2
Dissect between the submucosal and muscular layers to create a submucosal tunnel, extending the dissection 1-2 cm distal to the lesion to ensure adequate working space 1
The tunnel provides a confined working space that enhances scope stability and provides natural traction on the lesion during dissection 1
Step 2: Tumor Resection Within the Tunnel
Dissect around the entire circumference of the tumor using standard endoscopic resection techniques within the protected tunnel space 2, 3
Complete the resection en bloc by carefully separating the tumor from the surrounding muscularis propria layer 2, 3
The mucosal flap overlying the tunnel minimizes extravasation of luminal contents during the dissection process 1
Step 3: Specimen Extraction
Remove the resected tumor through the submucosal tunnel and mucosal entry point 1, 2
Size limitations apply: lesions larger than 3-4 cm are difficult to extract through the tunnel and may require conversion to exposed full-thickness resection 1
Step 4: Mucosal Closure
Close the mucosal incision site with several endoscopic clips to restore luminal integrity after tumor extraction 1, 2
Endoscopic closure of the mucosal flap is generally easier than attempting closure of a large defect after exposed endoscopic full-thickness resection 1
Critical Technical Requirements
General anesthesia with endotracheal intubation is mandatory to allow positive-pressure ventilation and control of capnoperitoneum/capnomediastinum 4
Carbon dioxide insufflation is required because of its rapid absorption and lower risk of adverse events compared to air 4, 5
Prophylactic intravenous antibiotics must be administered given the potential for luminal contamination 4, 5
Peritoneal decompression needles must be readily available to manage pneumoperitoneum if it occurs during the procedure 4
Expected Outcomes and Complications
En bloc resection rates range from 78.7% to 95% with complete (R0) resection rates between 97.1% and 100% 4, 2, 3
Air-leak complications occur in approximately 15% of cases (pneumothorax, subcutaneous emphysema, pneumomediastinum) and are managed conservatively 1, 4
Perforation rate is approximately 5.6%, with all events successfully treated without surgery 1, 4
Complication rates are significantly higher for lesions originating in the deeper muscularis propria layer (70%) compared to superficial muscularis propria layer (1.3%) 2
Common Pitfalls to Avoid
Do not attempt STER for lesions >3-4 cm as extraction through the tunnel becomes technically prohibitive and conversion to exposed resection is often required 1, 4
Avoid STER in locations not reachable via a straight-line endoscopic approach (certain gastric fundus locations) as tunnel creation becomes extremely challenging 4, 5
STER should only be performed by endoscopists highly skilled in advanced tissue-resection techniques, particularly those experienced with ESD or peroral endoscopic myotomy (POEM) 4