Third Space Endoscopic Surgery: What It Is and Why Very Few Surgeons in India Can Actually Do It
In most surgical procedures, you either operate on the surface — skin, mucosa, the lining of an organ — or you open the body to work on its contents. For most of medicine's history, those were the only two options. If something was wrong inside the wall of the gut — not on its inner surface, not outside in the abdomen, but actually within the tissue of the bowel wall itself — you had a problem. The only way to reach it was to cut through.
Third space endoscopic surgery changed that.
It's one of the most technically demanding subspecialties in gastroenterology, and one of the reasons I was asked to introduce it here in Andhra Pradesh is that the number of surgeons in India trained to perform the full range of third space procedures remains genuinely small — even as awareness of the conditions it treats is growing.
What Are the Three Spaces?
To understand why 'third space' is such a meaningful term, it helps to understand what the first two are.
• The first space is the interior of the gut — the lumen. This is where conventional diagnostic and therapeutic endoscopy has always operated: looking at the stomach lining, removing polyps, placing stents.
• The second space is the peritoneal or thoracic cavity — the space outside the gut, inside the abdomen or chest. Conventional surgery works here: laparoscopic and open operations access the organs by going through the abdominal wall.
• The third space is neither of these. It's the submucosal layer — the tissue that sits between the inner lining of the gut and the muscular wall beneath it. It's a virtual space: it doesn't exist as an open cavity until you create it, by carefully separating the lining from the muscle layer using fluid injection and precise dissection.
• Third space endoscopy operates in this submucosal tunnel. An endoscope enters through the mouth or the anus — no skin incision anywhere — creates a tunnel in the gut wall, performs the necessary procedure within that tunnel, and then seals the entry point with clips. The overlying mucosa remains intact throughout, which is what makes the approach so safe compared to open surgery.
Why This Matters Clinically
The significance of third space endoscopy is that it gave surgeons and endoscopists access to conditions that previously required one of two difficult choices: thoracoscopy (operating inside the chest cavity) or open abdominal surgery, both of which carry real risks and prolonged recovery for what are often benign or early-stage conditions.
Third space endoscopy replaced those options — in appropriate cases — with a procedure that:
• Has no skin incision
• Requires no chest or abdominal entry
• Is performed entirely through the mouth
• Involves a hospital stay of one to three days
• Results in recovery measured in days to weeks rather than months
The Procedures That Fall Under Third Space Endoscopy
POEM — Peroral Endoscopic Myotomy
The procedure that started the third space endoscopy era. In POEM, a submucosal tunnel is created in the esophagus to access and cut the muscle fibres of the lower esophageal sphincter — treating achalasia and related motility disorders without abdominal surgery. I was among the first ten surgeons in South India to perform POEM, and it is described in detail in a separate blog on this site.
STER — Submucosal Tunneling Endoscopic Resection
STER uses the same tunneling principle to remove tumours growing within the muscular wall of the esophagus or stomach. Rather than opening the chest to reach an esophageal leiomyoma or GIST, a submucosal tunnel is created, the tumour is dissected free from within the tunnel, removed through the endoscope, and the entry point is closed. No thoracoscopy. No chest tube. Discharge within two to three days. STER is discussed in detail in the next blog.
G-POEM — Gastric POEM for Gastroparesis
The same tunneling technique applied to the pylorus — the valve between the stomach and the small intestine. In severe, medically refractory gastroparesis (paralysis of the stomach's emptying mechanism), G-POEM cuts the pyloric muscle through a submucosal tunnel, allowing the stomach to empty normally again. An alternative to open pyloroplasty.
Z-POEM — Zenker's POEM
Zenker's diverticulum is a pouch that forms in the back of the throat where the esophagus begins. It causes food to pool and regurgitate, and a tight cricopharyngeal muscle is typically responsible. Z-POEM cuts this muscle through a submucosal tunnel created in the throat, treating the diverticulum without any neck incision.
D-POEM — Diverticulum POEM
Similar tunneling-based myotomy applied to epiphrenic diverticula — pouches at the lower end of the esophagus — which were previously treated by open or thoracoscopic esophageal surgery.
ESTD — Endoscopic Submucosal Tunnel Dissection for Early Cancers
For early-stage cancers that have not penetrated beyond the submucosal layer, endoscopic tunnel dissection through the third space can achieve curative en bloc resection — complete removal of the tumour as a single specimen — without open surgery. This requires precise technique and careful pre-operative staging with endoscopic ultrasound to confirm that the cancer is confined to the appropriate depth.
Why the Number of Practitioners Is So Limited
Third space endoscopy is not a single procedure — it is a skill set that takes years to develop. The learning curve for each procedure is steep, and the margin for error in the submucosal space is small. Complications — perforation of the mucosal layer, bleeding within the tunnel, insufflation-related problems — require immediate recognition and management by someone who has trained extensively in this environment.
Globally, third space endoscopy emerged from academic centres in Japan, Europe, and the US, and its spread to India has been gradual. The number of practitioners in India with experience across the full spectrum of third space procedures — POEM, STER, G-POEM, Z-POEM — remains in the dozens, not hundreds. In Andhra Pradesh, I introduced these procedures to a region that previously had no local access to them.
This isn't a claim to uniqueness for its own sake. It's a practical clinical point: if you or someone you know is being told they need open chest or abdominal surgery for a condition that could potentially be managed endoscopically, it is worth finding out whether a third space approach is applicable. The answer requires someone with specific expertise to assess.
Who Are the Patients Who Benefit from Third Space Procedures?
• Patients with achalasia or esophageal motility disorders (POEM)
• Patients with benign submucosal tumours of the esophagus — leiomyomas, GISTs — that would otherwise require thoracoscopic or open surgery (STER)
• Patients with severe, drug-resistant gastroparesis who have not responded to medications, dietary changes, or gastric electrical stimulation (G-POEM)
• Patients with Zenker's diverticulum causing food regurgitation and aspiration risk (Z-POEM)
• Patients with early-stage esophageal or gastric cancers confirmed to be within the submucosal layer on EUS staging (ESTD)
Each of these conditions has specific eligibility criteria. Not every patient with achalasia is a POEM candidate. Not every esophageal tumour is suitable for STER. The evaluation includes endoscopy, endoscopic ultrasound (EUS), and sometimes manometry — and the decision has to be made by someone who has performed enough of these procedures to know the limits as clearly as the indications.
If you have been evaluated for any of these conditions, or if a referring specialist has discussed third space endoscopy as a possible approach for your case, I am happy to review your investigation results and advise on whether an endoscopic approach is appropriate for you.
Book a consultation at Medicover Hospitals, Secunderabad — call +91 9154532511 or WhatsApp the same number.
