Peroral endoscopic myotomy (POEM) is an evolving minimally invasive endoscopic surgical procedure, with no skin incision, intended for long-term recovery from symptoms of esophageal achalasia. POEM was developed based on both the already established surgical principles of esophageal myotomy and the advanced techniques of endoscopic submucosal dissection. This article relates how POEM was developed, and its use in practice is reported and discussed. As an extension of the POEM technique, submucosal endoscopic tumor resection is introduced.
Key points
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The development of snare polypectomy with electrocautery opened the door for therapeutic endoscopy in the gastrointestinal tract.
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At present, endoscopic submucosal dissection (ESD) consists of endoscopic microsurgery using a flexible endoscope.
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In both ESD and peroral endoscopic myotomy (POEM) if either the mucosa or the muscle layer are kept intact, neither peritonitis nor mediastinitis may occur, because either the mucosa or the muscle layer acts as a strong barrier.
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POEM is performed under general anesthesia with endotracheal intubation, keeping the patient in the supine position.
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Another major advantage of POEM is the flexibility of myotomy length.
Introduction
Peroral endoscopic myotomy (POEM) is an evolving minimally invasive endoscopic surgical procedure, with no skin incision, intended for long-term recovery from symptoms of esophageal achalasia. POEM is considered one of the best applications of NOTES (Natural Orifice Transluminal Endoscopic Surgery). The first case was performed on September 8, 2008 at Showa University Northern Yokohama Hospital. Since then more than 390 achalasia cases have been treated with the POEM procedure in this hospital, with no major complications. POEM was developed based on both the already established surgical principles of esophageal myotomy and the advanced techniques of endoscopic submucosal dissection (ESD). This article relates how POEM was developed, and its use in practice is reported and discussed. As an extension of the POEM technique, submucosal endoscopic tumor resection is introduced.
Introduction
Peroral endoscopic myotomy (POEM) is an evolving minimally invasive endoscopic surgical procedure, with no skin incision, intended for long-term recovery from symptoms of esophageal achalasia. POEM is considered one of the best applications of NOTES (Natural Orifice Transluminal Endoscopic Surgery). The first case was performed on September 8, 2008 at Showa University Northern Yokohama Hospital. Since then more than 390 achalasia cases have been treated with the POEM procedure in this hospital, with no major complications. POEM was developed based on both the already established surgical principles of esophageal myotomy and the advanced techniques of endoscopic submucosal dissection (ESD). This article relates how POEM was developed, and its use in practice is reported and discussed. As an extension of the POEM technique, submucosal endoscopic tumor resection is introduced.
Advancement in technology from endoscopic mucosal resection/ESD to POEM
The development of snare polypectomy with electrocautery opened the door for therapeutic endoscopy in the gastrointestinal tract. With less risk of bleeding, snare polypectomy quickly became the standard treatment for polypoid lesions. However, application of snare polypectomy to nonpolypoid lesions was technically difficult and remained unsolved. Endoscopic mucosal resection (EMR) was then developed for resection of flat mucosal lesions. Dehyle and colleagues reported endoscopic resection of mucosa combined with submucosal injection. Submucosal injection creates a mucosal bleb, which is followed by snare resection. Later, EMR using a suction cap (EMR-C) was developed by the authors. EMR-C was then further modified to EMR using a band ligator, which accelerated the popularization of the technique. EMR does enable the resection of flat mucosal lesions, but the size of resection is somewhat limited. Large mucosal lesions can be successfully excised in a piecemeal fashion through repeated EMRs, although the resulting specimens are fragmented.
To acquire large, one-piece specimens for accurate histopathologic evaluation, the novel method of ESD was developed by Ono. To successfully complete ESD, various basic techniques are used such as submucosal injection, mucosal cutting, submucosal dissection, and hemostasis. ESD currently consists of endoscopic microsurgery using a flexible endoscope. The fundamental techniques used in the POEM procedure (submucosal injection, mucosal incision, submucosal tunneling, and hemostasis) are very similar to those of ESD.
History of achalasia treatment
Achalasia (the word itself is a Greek term that means “does not relax”) is a chronic benign disease with a subtle onset and symptoms that may progress gradually for years before an exact diagnosis can be made. It is the most common primary motility disorder of the esophagus; however, it occurs rarely, with an annual incidence of approximately 0.03 to 1 per 100,000 per year. Achalasia affects men and women equally and may occur at any age. Despite an increasing understanding of its pathophysiology, the etiology of achalasia remains largely unknown, and all current treatments have different advantages and drawbacks.
Therapy has focused mainly on the forced relaxation of the lower esophageal sphincter (LES) by endoscopic or surgical means. As few randomized controlled trials have attempted to determine the optimal strategy, treatment still varies widely. First-line endoscopic treatments are botulinum toxin (Botox) injection and esophageal balloon dilatation. Endoscopic pneumatic balloon dilatation temporarily relieves dysphagia in up to 70% of cases, and is still widely performed because of its relative noninvasiveness. However, it is associated with a potential risk of esophageal perforation (2.5%) and frequent recurrences. The cumulative 5-year remission rate of pneumatic dilatation for achalasia is reported to be between 50% and 70%. If these interventions are ineffective, surgical myotomy is generally indicated. Surgical myotomy was originally reported by Heller in 1913, and consisted of 2 longitudinal cuts of approximately 8 cm on the anterior and posterior esophageal wall, which included an approximately 2-cm cut on the dilated part (esophagus) and a short cut over the cardia into the fundus. This approach suggests that complete release of the LES is mandatory to achieve complete relief from achalasia symptoms. Later, bilateral myotomy was modified to single myotomy, but the basic principle remained unchanged. Although surgical myotomy provides the best solution for esophageal achalasia, it still has limitations and failures. In particular, gastroesophageal reflux disease (GERD) may occur in up to 30% of cases following a Heller myotomy; it is generally considered to require an additional antireflux procedure, such as Dor fundoplication.
Laparoscopic myotomy is a less invasive technique that significantly reduces the morbidity of open surgery. However, it still requires several abdominal incisions and also involves dissection of the normal esophageal hiatus, which may cause potential hiatal hernia.
Endoscopic myotomy
The concept of endoscopic myotomy for the treatment of achalasia was first reported in a case series in 1980. However, the direct-incision method through the mucosal layer that was used in this study was not considered a safe and reliable approach, and has not been followed further. Pasricha and colleagues reported the possibility of endoscopic myotomy through a submucosal tunnel in a porcine model. Sumiyama and colleagues also reported the technical feasibility of submucosal tunneling in a porcine model, while Perretta and colleagues have also reported the safety and effectiveness of endoscopic submucosal esophageal myotomy in a pig model. Based on this experimental background, the authors have refined the techniques for clinical application to enable performance of endoscopic myotomy in humans, namely, POEM.
What are the technical differences between ESD and POEM?
ESD was first developed by Ono to resect intramucosal cancers endoscopically in a 1-piece nonfragmented specimen. Mucosal lesions (high-grade dysplasia or intramucosal carcinoma) resected in a single piece allow complete histopathologic assessment, including horizontal spread and vertical infiltration of the tumor. In ESD, the mucosal layer is resected together with a major part of the submucosal layer while the muscular layer is absolutely preserved. Muscle layer and serosa (or adventitia) acts as a barrier against leakage of gastrointestinal fluid toward the mediastinum and peritoneal cavity. If the muscular layer is incidentally disrupted, this indicates perforation of the gastrointestinal wall, which doubtless causes mediastinitis or peritonitis. Perforation should be immediately closed with endoscopic clip(s).
In the POEM procedure, the muscle layer is intentionally dissected and divided. As a result, the mediastinum is eventually open to submucosal space. In the POEM procedure the preserved mucosa works as a strong barrier to isolate gastrointestinal lumen from the mediastinum or peritoneum. The advanced endoscopic technology of POEM enables dissection of the muscle layer through a submucosal tunnel, without tearing the covering mucosa. Complete endoscopic myotomy had never taken place in clinical experience before the development of the POEM procedure.
Finally, what is learned from both ESD and POEM is that if either the mucosa or muscle layer is kept intact, neither peritonitis nor mediastinitis may occur, because either the mucosa or the muscle layer acts as a strong barrier ( Fig. 1 ).
