Initial longitudinal mucosal incision is performed following submucosal injection of a lifting solution.The submucosal space stained with the dilute methylene blue solution can be seen
The submucosal dissection is perfomed in the deep submucosal space to avoid injury to the overlying mucosal flap which can be appreciated at the upper portion of the image
Luminal view of the completed submucosal tunnel extending from the mucosotomy to the pylorus. Pallor of the mucosa is related to the dilute epinephrine which is mixed into the lifting solution
Submucosal view near the end of the myotomy process. A thin residual strand of pyloric sphincter muscle is seen crossing horizontally. Care should be taken to avoid injury to the overlying duodenal mucosa which is visible draping over at the upper portion of the image
Closure of the musocal incision utilizing endoscopic clips is seen
Radiologic upper GI study perfomed the day following the procedure demonstrates intact closure of the mucosotomy
The first human experience with POP was reported by Khashab et al. in 2013. A 27-year-old female with diabetic gastroparesis, daily symptoms of nausea, vomiting, and multiple admissions for refractory symptoms and dehydration was treated with POP. No complications were reported and objective and subjective results confirmed the success of treatment . A subsequent early case series was reported by Shlomovitz et al. documenting seven nondiabetic patients with refractory gastroparesis treated with the POP procedure. In this series, the most common cause of gastroparesis was idiopathic (n = 5). Two patients had postsurgical gastroparesis based on a history of prior foregut surgery. Six procedures were performed under laparoscopic guidance, given that patients required other concurrent laparoscopic procedures. A purely endoscopic procedure was performed in one patient who didn’t require an additional laparoscopic procedures.
POP was technically successful in all seven cases, and there were no intraoperative complications. Delayed complications related to the procedure consisted of an upper GI bleed 2 weeks post-procedure necessitating a blood transfusion. This occurred in a patient that did not comply with the usual regimen of postoperative high-dose PPI use. Upper endoscopy demonstrated a 1-cm ulcer in the pyloric channel, with an exposed vessel that was clipped resulting in complete resolution of the bleeding. In this patient series, six of the seven patients reported symptom improvement or resolution at 6-month follow-up. Objective nuclear medicine gastric emptying studies (GES) were available in five of the patients. In four out of these five patients, follow-up GES documented successful normalization of their gastric emptying .
POP has also been shown to be effective in the treatment of gastroparesis caused by vagal injury post esophagectomy and post fundoplication [52, 53].
Some technical differences do exist between the POP and the POEM techniques. Unlike in POEM we prefer to keep a fairly short submucosal tunnel with the mucosal incision that is performed only about 2–3 cm proximal to the pylorus. Also the myotomy itself is fairly restricted to the pylorus and only extends proximally by about 1 cm. During the pyloromyotomy, no specific attempt is made to selectively divide only the circular muscular layer, and it is typically divided in a full thickness fashion down to the serosal layer. Special attention must be paid when performing the distal portion of the pyloromyotomy since the duodenal mucosa will drape over it in a perpendicular direction and could be easily perforated during this portion of the dissection. Finally, there is still some disagreement as to the optimal location to perform the myotomy. We prefer to perform the pyloromyotomy on the posterior aspect of the greater curvature, adjacent to the retroperitoneum, to benefit from the natural positioning of the endoscope. An argument however can be made to perform the myotomy along the anterior aspect so that the procedure can more easily be converted to a laparoscopic pyloroplasty in case of an endoscopic full thickness perforation.
The success of POEM expanded the indications and the acceptance of the endoscopic submucosal dissection techniques. This has an especially marked effect in the Western world where these techniques were much less well known and practiced as compared to Asia. The greatest testament to this may be the increasing reports in the Western world of gastroenterologists and surgeons performing advanced endoscopic techniques such as endoscopic tumor enucleation and endoscopic pyloromyotomy.
Further studies with larger number of patients are needed to determine long-term outcomes and indications of those endoscopic therapies. Endoscopic tumor enucleation particularly must be well studied to ensure that long-term oncologic results remain equivalent to laparoscopic or open resection. With time and operator experience, even more advanced techniques such as endoscopic full thickness resection (EFTR) will also gain popularity.
Significant challenges however remain with respect to adequate physician training to perform these advanced procedures. Only few centers have evaluated the learning curve for POEM. Kurian et al. reported that mastery of operative technique in POEM can be measured by the decrease in length of procedure and incidence of inadvertent mucosotomies. He found that 20 cases are needed to reach mastery . Procedure time however can be quite variable between patients and can largely depend on prior esophageal interventions . Patel et al. subsequently defined efficiency after 40 POEMs and mastery after 60 POEMs elevating the threshold established by Kurian and colleagues . Obtaining this required level of experience can be quite challenging especially in the setting of such a rare disorder such as achalasia. Future research must therefore also focus on improvement in the training and simulation of these procedures. With time the available endoscopic surgical platforms will continue to improve and evolve making these techniques accessible to an ever increasing group of practitioners.
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