Submucosal endoscopy with a mucosal flap (SEMF) safety valve technique is a global concept in which the submucosa is a free working space for endoscopic interventions. A purposefully created intramural space provides an endoscopic access route to the deeper layers and into the extraluminal cavities. The mucosa overlying the intramural space is protective, reducing contamination during natural orifice transluminal endoscopic surgery (NOTES) procedures and providing a sealant flap to repair the entry point and the submucosal space. In addition to NOTES, SEMF enables endoscopic achalasia myotomy, histologic analysis of the muscularis propria, and submucosal tumor removal.
Key points
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Submucosal endoscopy with a mucosal flap (SEMF) safety valve technique is a global concept that uses the submucosa as a free working space for endoscopic interventions.
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A purposefully created intramural space provides an endoscopic access route to the deeper layers and into the extraluminal cavities.
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The mucosa overlying the intramural space is protective, reducing contamination during natural orifice transluminal endoscopic surgery (NOTES) procedures and providing a sealant flap to repair the entry point and the submucosal space.
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In addition to NOTES, SEMF has been used to enable endoscopic achalasia myotomy; histologic analysis of the muscularis propria, including neural components; and submucosal tumor removal.
Introduction
Research into endoscopic tissue excision has focused on pursuing methods to obtain larger specimens. The eventual development of endoscopic submucosal dissection (ESD) enabled radical en bloc removal of a mucosal lesion regardless of size. During efforts to accomplish widespread endoscopic mucosal resection (EMR) in the Mayo Clinic Developmental Endoscopy Unit (DEU), the authors observed that the mucosa could be separated from the underlying submucosa (ie, delamination) with relative ease. The potential value of delamination later resurfaced. Natural orifice transluminal endoscopic surgery (NOTES) established a path for flexible endoscopy beyond the gut wall. During the NOTES experience, the authors recognized that with delamination of the mucosa from the submucosa, the submucosal layer could be converted into a practical endoscopic working space. Pilot animal studies demonstrated that a purposefully created free space within the submucosa would provide off-set tunneled access to the deeper layers as well as a safer and cleaner portal into the extraluminal cavities for NOTES procedures compared with direct full-thickness viscerotomy ( Fig. 1 ). Conversely, once the submucosa has been opened, the overlying mucosa can be excised more safely from inside the submucosa out into the gut lumen. This inside-out technique could be a safer and easier alternative to the current labor-intensive ESD for en bloc resection of mucosal disease.
Intramural endoscopy has attracted great attention internationally. A variety of promising spin-offs have developed and pioneering clinical studies have already revealed practical advantages of this novel application for gastrointestinal (GI) endoscopy.
Introduction
Research into endoscopic tissue excision has focused on pursuing methods to obtain larger specimens. The eventual development of endoscopic submucosal dissection (ESD) enabled radical en bloc removal of a mucosal lesion regardless of size. During efforts to accomplish widespread endoscopic mucosal resection (EMR) in the Mayo Clinic Developmental Endoscopy Unit (DEU), the authors observed that the mucosa could be separated from the underlying submucosa (ie, delamination) with relative ease. The potential value of delamination later resurfaced. Natural orifice transluminal endoscopic surgery (NOTES) established a path for flexible endoscopy beyond the gut wall. During the NOTES experience, the authors recognized that with delamination of the mucosa from the submucosa, the submucosal layer could be converted into a practical endoscopic working space. Pilot animal studies demonstrated that a purposefully created free space within the submucosa would provide off-set tunneled access to the deeper layers as well as a safer and cleaner portal into the extraluminal cavities for NOTES procedures compared with direct full-thickness viscerotomy ( Fig. 1 ). Conversely, once the submucosa has been opened, the overlying mucosa can be excised more safely from inside the submucosa out into the gut lumen. This inside-out technique could be a safer and easier alternative to the current labor-intensive ESD for en bloc resection of mucosal disease.
Intramural endoscopy has attracted great attention internationally. A variety of promising spin-offs have developed and pioneering clinical studies have already revealed practical advantages of this novel application for gastrointestinal (GI) endoscopy.
Submucosal endoscopy with mucosal flap safety valve technique and off-set access to extraluminal spaces for NOTES
Submucosal endoscopy with a mucosal flap (SEMF) safety valve technique was devised as a method to convert the submucosa into a working space for endoscopic intervention and to provide an off-set entry point into the extraluminal space to enable NOTES (see Fig. 1 ). The unique feature of this technique is the protective function of the overlying mucosa, which minimizes contamination from luminal contents and provides a sealant flap to the submucosal space after any off-set exit from the gut wall into a body cavity ( Fig. 2 ).
The submucosal space, or tunnel, in more limited applications of SEMF, requires a 4 to 5 cm length to provide a safety flap valve. In the authors’ experience, a 5 to 10 cm long tunnel is superior; the greater length acts as an added safety measure during NOTES procedures for less risk of extraluminal contamination. The SEMF procedure is initiated by creation of a submucosal fluid cushion (SFC) to access the submucosa and initiate the anticipated route of the submucosal tunnel. The SFC is critical for entering the dissection plane and for preventing inadvertent full-thickness injury. Saline works well for quick procedures; however, viscous solutions, such as hyaluronate and hydroxypropyl methylcellulose, remain localized longer, creating a durable SFC and avoiding of supplemental injections. To supplement the SFC and facilitate dissection, a thiol compound, mesna, can be added to the injectate. Mesna chemically softens the submucosa and facilitates dissection by dissolving the disulfide bonds of protein fibers. Due to the lack of viscosity, mesna must be used in combination with one of the viscous solutions mentioned above. Following instillation of the SFC, a 5 to 10 mm mucosal incision is made with a needle knife to pass tools through for the actual submucosal dissection. The direction of the mucosal incision is horizontal for a gastric tunnel, to avoid tearing the mucosal incision during the dissection and to ease closure. It is longitudinal for an esophageal tunnel, primarily to facilitate clip closure within the narrow esophageal lumen. Once the early submucosal space is made large enough to accommodate inserting the tip of the endoscope, the dissection is continued with the tip of the scope inside the expanding submucosal tissue space. A transparent cap can aid visualization of the dissection plane. The traditional ESD technique using repetitive electrosurgical dissection can be used to create a tunnel. The tunnel size is ideally restricted to the minimum necessary for endoscopic insertion to preserve the blood supply of the overlying mucosal sealant flap and avoid inadvertent coagulation necrosis of the protective mucosa flap.
In developmental investigations, the authors recognized that the blunt balloon dissection technique provides instant mechanical cleavage of the submucosal tissue plane and facilitates creation of a longitudinal tunnel. Repetitive balloon dissection with a biliary retrieval balloon catheter was originally used with success. A unique cylindrical balloon dissector has been designed for efficient tunnel creation (SuMO, Apollo Endosurgery, Austin, TX) ( Fig. 3 ). Initially, the self-advancing hydraulic balloon is stowed within the catheter sheath, unfolding as it advances and distends. The advancing balloon follows the submucosal tissue plane, readily cleaving it without wire guidance. A submucosal tunnel up to 10 cm can be immediately created with a single balloon expansion ( Fig. 4 ). The width of the tunnel can be controlled with the variation of the balloon diameter. Although significant bleeding has not been encountered, balloon compression may incidentally provide a hemostatic effect. It has yet to be investigated whether the mechanical balloon dissection technique can completely replace traditional needle knife dissection. Future study should ensure that balloon dissection is effective in the setting of mucosal scaring (without damaging the overlaying mucosa and the muscularis). The submucosal space is readily closed without special skills with simple approximation of the mucosal entry point using endoclips after the decompression of the tunnel (see Fig. 2 ). Using SEMF as an off-set access for NOTES (gastric) viscerotomy, we were able to directionally perform the submucosal tunneling to direct the endoscope to the gallbladder and perform a cholecystectomy. Although access to the upper abdominal cavity higher than the level of the stomach is inherently restrictive for any transgastric approach because of the mechanical limitations imposed by current flexible endoscopes, the creation of a cephalad submucosal tunnel in retroflexed position overcomes the difficulties with direct transgastric access to the upper abdominal cavity. Kitano and colleagues reported the first clinical experience of anterior transgastric peritoneal access through the cephalad submucosal tunnel created with traditional needle knife dissection. Peritoneoscopy under general anesthesia with laparoscopic monitoring was performed as a part of the preoperative evaluation of patients who have pancreatic cancer.
