A Look into the Future of Endoscopic Submucosal Dissection and Third Space Endoscopy: The Role for Robotics and Other Innovation

Endoscopic resection has been widely applied especially in endoscopic submucosal dissection and third space endoscopy (TSE). Flexible endoluminal robotics allow performance of endoscopic submucosal dissection with exposure of the submucosal plane for precise dissection using two robotic arms. The introduction of TSE revolutionized the horizon of therapeutic endoscopy to the submucosal space beneath and beyond the mucosa. Advantages of TSE include avoidance of full thickness incision in gastrointestinal tract through the submucosal tunneling for performance of peroral endoscopic myotomy and submucosal tunneling endoscopic resection. In future, robotic-driven devices should be developed to enhance performance of complex endoluminal procedures and TSE.

The Journey from Endoscopic Submucosal Dissection to Third Space Endoscopy

With the advent of endoscopic submucosal dissection, a variety of endoscopic devices including knives and high-frequency electrosurgical unit have become available. In addition, the concept of natural orifice transluminal endoscopic surgery pushed flexible endoscopic surgery ahead. In this review, the birth of peroral endoscopic myotomy and its expansion into the field of submucosal endoscopy are reviewed.

Indications and Outcomes of Per Oral Endoscopic Myotomy from Mouth to Anus

Third space endoscopy or submucosal endoscopy using a mucosal flap valve allows secure access to the submucosal and deeper layers of the gastrointestinal tract without the risk of a full-thickness perforation. This allows the performance of submucosal tunneling and myotomy for spastic segments of the gastrointestinal tract. Per oral endoscopic myotomy (POEM) has been described for the treatment of achalasia cardia and other spastic esophageal disorders and is widely implemented. Endoscopic pyloromyotomy (G-POEM) has been performed for the treatment of refractory gastroparesis. Z-POEM for Zenker's diverticulum, D-POEM for epiphrenic diverticulum, and per-rectal endoscopic myotomy for treatment of Hirschsprung's disease are described..

Submucosal Tunneling Techniques for Tumor Resection

The concept of third space endoscopy is based on the principle that the deeper layers of the gastrointestinal tract can be accessed by tunneling in the submucosal space and maintaining the integrity of the overlying mucosa. The mucosal flap safety valve enabled endoscopists to use submucosal space securely. The era of third space endoscopy started with peroral endoscopic myotomy for treatment of achalasia and has expanded to treat various other gastrointestinal disorders, such as mucosal lesions, submucosal tumors, extraluminal tumors, and refractory gastroparesis, Zenker diverticulum, and restoration of the completely obstructed esophageal lumen. Third space endoscopy rapidly emerged as a minimally invasive alternative to conventional surgery. Many studies discovered that this technique is safe and effective with excellent outcomes. Our review focused on the indications, techniques, clinical management, and adverse events of submucosal tunneling techniques for tumor resection.

Recent advances in third space or intramural endoscopy

Third space endoscopy or intramural endoscopy is based on the principle that the deeper layers of the gastrointestinal tract can be accessed by tunneling in the submucosal space and maintaining the integrity of the overlying mucosa. The era of third space endoscopy started with peroral endoscopic myotomy (POEM) for treatment of achalasia and has expanded to treat various other gastrointestinal disorders. The technique is also currently used for treatment of refractory gastroparesis, Zenker’s diverticulum (ZD), resection of subepithelial tumors and early cancers of the gastrointestinal tract and Hirschsprung’s disease (HD). These procedures are rapidly emerging as minimally invasive alternatives to conventional surgery. They are safe and effective with excellent outcomes. This review focuses on the evolution and current applications of third space endoscopy in various gastrointestinal disorders. Key points: (1) Third space or intramural endoscopy initially started with the POEM procedure for treatment of achalasia; (2) Advancements in procedural techniques have expanded its application to treat other gastrointestinal disorders such as refractory gastroparesis, ZD, HD, resection of subepithelial tumors and early gastrointestinal cancers; (3) These procedures are highly effective with excellent outcomes and low complication rates; and (4) Third space endoscopic procedures are rapidly emerging as minimally invasive alternatives to conventional surgery.

Principles of Intramural Surgery

Intramural surgery is a minimally invasive surgical technique based on flexible endoscopy. The first step involves the initial mucosal incision for entry point. Then a submucosal tunnel is dissected to the site of the target anatomy. The procedure performed may include myotomy or lesion removal. When complete, the initial mucosal incision is closed. This technique separates the mucosal flap from the surgical site, minimizing the risk of full-thickness perforation and gastrointestinal leakage. Peroral endoscopic myotomy is the most studied application of intramural surgery but other procedures have emerged. This article explores principles of intramural surgery and summarizes its applications.

Peroral endoscopic tumor resection (POET) with preserved mucosa technique for management of upper gastrointestinal tract subepithelial tumors

BACKGROUND

Third space endoscopy technique facilitates therapeutic endoscopy in subepithelial space. This study aimed to investigate peroral endoscopic tumor resection (POET) with preserved mucosa technique for upper gastrointestinal tract subepithelial tumors (UGI-SETs) removal.

METHODS

Between February 2011 and December 2019, consecutive patients with SETs of esophagus and stomach who underwent POET for enlarging size during follow-up, malignant endoscopic ultrasound features or by patient's request were enrolled. Demographic, endoscopic and pathological data were analyzed retrospectively.

RESULTS

Totally 18 esophageal (mean ± SD age, 55.23 ± 4.15 year-old, 38.89% female) and 30 gastric (52.65 ± 2.43 year-old, 53.33% female) SETs in 47 patients (one with both esophageal and gastric lesions) were resected. The mean (± SD) endoscopic/pathological tumor size, procedure time, en-bloc/complete resection rate, and hospital stays of esophageal and gastric SET patients were 12.36 (± 7.89)/11.86 (± 5.67) and 12.57 (± 6.25)/12.35 (± 5.73) mm, 14.86 (± 6.15) and 38.21 (± 15.29) minutes, 88.89%/94.44% and 86.77%/93.30%, and 4.14 (± 0.21) and 4.17 (± 0.20) days, respectively. The overall complication rate was 18.75%, including 6 self-limited fever and 3 pneumoperitoneum relieved by needle puncture. There was no mortality or recurrence reported with mean follow-up period of 23.74 (± 4.12) months.

CONCLUSIONS

POET is a safe and efficient third space endoscopic resection technique for removal of UGI-SETs less than 20 mm. Long term data are warranted to validate these results.

Esophageal Third Space Endoscopy: Recent Advances

PURPOSE OF THE REVIEW

The novel concept of third space endoscopy was first applied to humans in 2008 for the management of achalasia through peroral endoscopic myotomy (POEM) procedure. Over the ensuing 10 years, this revolutionary procedure, which started in Japan, has been adopted and mastered by surgeons and gastroenterologists across the globe. In this article, we review the recent innovations and applications of third space endoscopy in the management of esophageal disorders.

RECENT FINDINGS

With experience and innovation, the application of third-space endoscopy has extended beyond achalasia, and currently, it is used in the management of other esophageal disorders including, spastic esophageal disorders, subepithelial tumors, complete esophageal obstruction, and esophageal diverticula. The recent advances in third space endoscopic procedures have not only permitted endoscopic access to places, previously thought impossible, but also enabled the precision of surgery along with reduced peri-operative morbidity due to its minimally invasive nature. While short- and mid-term outcome studies have shown excellent results, we eagerly await the long-term outcome studies before these procedures could be established as the procedures of choice.