Rectal tumors extending to the dentate line (RTDL) represent a particularly challenging subtype of rectal cancer. The dentate line is a critical anatomical boundary inside the anal canal that marks the transition between the columnar epithelium of the rectum above and the squamous epithelium of the anal canal below.
This region is unique because it contains a dense network of blood vessels and sensory nerves. Surgery in this area carries specific risks: intraoperative bleeding is harder to control due to the rich venous plexus; postoperative pain tends to be more severe due to the abundant nerve supply; and the risk of bacteremia (bacteria entering the bloodstream) is elevated because the rectal venous plexus drains directly into the systemic circulation rather than through the portal system.
The narrow diameter of the anal canal (approximately 2.5 to 3 centimetres at the dentate line, compared to 4 to 5 centimetres in the upper rectum) combined with the constant contraction of the surrounding sphincter muscles severely limits the working space available to the surgeon or endoscopist. This makes both visualisation and instrument manipulation significantly more difficult than at other rectal locations.
Traditional surgical approaches to this region risk damage to the anal sphincter, the ring of muscle responsible for controlling continence. Sphincter damage can result in permanent faecal incontinence, a devastating complication that profoundly affects quality of life. This makes sphincter-preserving techniques like endoscopic resection particularly valuable when feasible.
Endoscopic submucosal dissection (ESD) is a minimally invasive technique performed through a standard endoscope (a flexible camera inserted through the anus) without any external incisions. It allows surgeons to remove superficial tumors of the bowel wall layer by layer from inside the bowel, using specialised endoscopic knives passed through the instrument channel of the scope.
The procedure works by first injecting a solution beneath the tumor to lift it away from the deeper muscle layer, creating a cushion of fluid in the submucosal space. The endoscopist then cuts around the lesion and dissects underneath it to remove it as a single intact piece (en bloc resection). This is critical for accurate pathological analysis of the resection margins - whether the entire tumor has been removed.
Compared to open or laparoscopic surgery, ESD offers important advantages: no abdominal incisions, faster recovery, shorter hospital stays, and preservation of organ function including the anal sphincter. For tumors confined to the mucosal layer (the innermost lining) without deep invasion, ESD can be curative. However, ESD is technically demanding and requires specialised training and experience, and it carries risks of bleeding and perforation.
When tumors are located at the dentate line or are associated with a diverticulum (a thin-walled outpouching of the bowel wall), these risks are substantially amplified. Performing ESD in a case that combines both a large tumor size, dentate line involvement, AND a diverticulum simultaneously is exceptionally rare and technically complex.
The case involved a 70-year-old male patient who presented with a 2-year history of altered bowel habits - yellow loose stools with occasional blood, occurring 2 to 3 times daily. He had no significant underlying medical conditions, no family history of hereditary bowel disease, and his blood tests, urine, and stool investigations on admission were all within normal ranges.
Colonoscopy revealed a large mass encompassing two-thirds of the rectal circumference, measuring approximately 7 centimetres by 8 centimetres and extending all the way to the dentate line. The lesion appeared as a nodular, cerebriform lateral spreading tumor with irregular pit patterns and increased, disorganised microvascularity under narrow-band imaging - features raising concern for high-grade or early malignant change. Biopsy confirmed high-grade intraepithelial neoplasia with focal intramucosal carcinoma.
To assess whether the tumor had invaded deeply or spread to lymph nodes - which would change the treatment approach entirely - the team performed a pelvic MRI. The MRI confirmed no lymph node involvement and no distant metastasis. Importantly, the MRI measured the invasive portion as only 2.6 by 2.1 centimetres (much smaller than the 7 by 8 centimetre colonoscopic measurement), because the MRI captures the invasive component while colonoscopy captures the full lateral spreading component including superficial areas.
Based on these findings, a multidisciplinary team (MDT) of gastroenterologists, gastrointestinal surgeons, radiologists, and pathologists concluded that the lesion was likely an early rectal carcinoma confined to the mucosal layer. Given the patient's age of 70, the tumor's proximity to the dentate line, and the patient's strong desire to preserve anal function, the MDT consensus was that ESD offered the best balance of oncologic safety and functional preservation.
The procedure faced three simultaneous major challenges: the large tumor size (nearly 8 centimetres) limiting visibility and increasing residual disease risk; dentate line involvement raising bleeding and pain risks; and a co-existing diverticulum increasing perforation risk. The surgical team used several carefully planned adaptations to address each challenge.
The most critical technical innovation was the use of a retrograde dissection strategy from the anal side. Rather than starting at the upper edge of the tumor and working downward, the endoscopist began by incising at the dentate line using a retroflexed endoscopic view (the scope bent back on itself), then proceeded upward in a stepwise manner. This approach maximised visibility in the narrow anal canal and allowed better control of the dissection plane.
To prevent bleeding, epinephrine was added to the submucosal injection solution, causing the small blood vessels to contract. The team also applied prophylactic electrocoagulation (electrocautery) to all visible submucosal vessels larger than 1 millimetre before cutting through them - a precautionary approach to minimise intraoperative haemorrhage.
The diverticulum - which lacks a muscular wall and therefore tears easily, risking perforation into the abdominal cavity - was managed by sealing its opening with three metal clips before dissection reached that area. This created a safe plane for dissection and prevented both perforation during the procedure and postoperative diverticulitis. After resection, the mucosal defect was intentionally left open rather than clipped shut, to prevent stricture formation in the narrow anal canal.
The ESD procedure was completed successfully without any intraoperative or immediate postoperative complications - no bleeding, no perforation, no anal pain, and no bacteremia. The patient was allowed water and oral nutritional supplements starting on day 2 after the procedure, progressed to a liquid diet on day 3, and was discharged home by day 7.
Pathological analysis of the resected specimen confirmed the final diagnosis as a conventional serrated adenoma with high-grade intraepithelial neoplasia and focal intramucosal carcinoma (pTis). The pTis classification indicates that the cancer was confined entirely to the innermost mucosal layer and had not penetrated through the muscularis mucosae (the thin muscle layer underlying the lining).
Critically, the horizontal and vertical resection margins were both negative (R0 resection) - meaning the tumor was completely removed with a clear rim of healthy tissue surrounding it on all sides. There was no evidence of lymphovascular invasion (cancer cells invading blood or lymph vessels), which would have indicated a risk of spread. These pathological features confirmed that the resection was curative.
At the one-year follow-up colonoscopy, there was no evidence of tumor recurrence or residual disease. The patient's anal function was preserved - he had normal continence and was able to resume normal activities within two weeks. He reported significant satisfaction with the treatment outcome and relief at avoiding major abdominal surgery.
The three main treatment options for rectal tumors near the dentate line are ESD, laparoscopic radical resection, and transanal endoscopic microsurgery (TEM). Understanding how they compare helps explain why ESD was the right choice for this patient.
Laparoscopic radical resection offers the highest certainty of complete removal and the most thorough lymph node dissection, making it the preferred approach when the tumor has invaded deeply or when lymph node spread is suspected. However, it requires 3 to 4 small abdominal incisions, carries a higher risk of sphincter damage (potentially requiring a permanent colostomy), and is associated with longer operative times of 2 to 3 hours and recovery periods of 10 to 14 days.
TEM (transanal endoscopic microsurgery) offers good visualisation for low rectal lesions and avoids abdominal incisions, but it is generally limited to tumors up to 5 centimetres in diameter - making it unsuitable for the 7 by 8 centimetre lesion in this case. ESD has no comparable size restriction for superficial lesions and its en bloc resection rates range from 85.7 to 100% in published series for dentate line tumors.
ESD preserves organ integrity and anal function, involves no abdominal incision, and allows recovery within 7 to 10 days. The evidence supporting ESD for diverticulum-associated colorectal tumors is also growing - published series have reported R0 resection rates of 95 to 96% with very low complication rates. This case adds to that evidence by demonstrating ESD's feasibility when all three high-risk features (large size, dentate line, diverticulum) are present simultaneously.
This report is a single case study, which is the most significant limitation. A single case, however successful, cannot establish the generalisability of the technique or confirm that the same approach would be safe and effective in other patients with similar presentations. The experience of one skilled centre with one patient cannot replace evidence from larger series.
The follow-up period of one year, while reassuring, is relatively short for a lesion of this size and histological subtype. Conventional serrated adenomas with high-grade dysplasia have a distinct biological profile and may carry a recurrence risk that becomes more apparent over longer follow-up periods. Longer surveillance is essential before declaring a curative outcome with full confidence.
The technical strategies used in this case are also operator-dependent. The successful outcome reflects the experience and skill of the specific endoscopy team involved. Replicating these techniques requires specialised training, and not all centres will have the necessary expertise to safely perform ESD for such complex lesions. Broader adoption of this approach would require investment in training.
The patient's own perspective is an important part of the story. He reported minimal postoperative pain, resumption of normal activities within 2 weeks, and significant relief at the one-year follow-up that his anal function was completely preserved. For an elderly patient who would have faced the risk of a permanent colostomy with surgical resection, the quality-of-life benefit of ESD was substantial and directly meaningful to his daily life.