Conformal sphincteric resection for ultra-low rectal cancer located below the dentate line: A pilot report

Sphincter-sparing surgery can be achieved in most cases of low rectal cancer with the development of intersphincteric resection. However, abdominoperineal resection is still inevitable for patients with tumours located below the dentate line. To address this, we have developed a procedure called conformal sphincteric resection (CSR) in which the corresponding part of the subcutaneous portion of the external anal sphincter and the perianal skin on the tumour side is removed to achieve a safe distal resection margin and lateral resection margin while the dentate line and the internal anal sphincter on the tumour-free side are preserved as much as possible, to achieve sphincter preservation without compromising oncological safety and functional acceptability, and to render tumour location no longer a contraindication for sphincter-sparing surgery. This is the first study to describe the concept, indication and surgical procedure of CSR and to report its preliminary surgical, oncological and functional results.

This is a retrospective, single-centre, single-arm pilot study conducted at Huashan Hospital, Fudan University. Demographic, clinicopathological, oncological and functional follow-up data were collected from 20 consecutive patients with rectal tumours located below the dentate line who underwent laparoscopic CSR by the same surgical team from June 2018 to March 2022.

The mean distance of the tumour's lower edge from the anal verge was 13.1 ± 6.0 mm. The mean distal resection margin was 10.6 ± 4.3 mm. All circumferential resection margins were negative. There were no instances of perioperative mortality. The complication rate was 25% but all were Clavien-Dindo Grade I. Among the 20 cases, 17 were diagnosed with adenocarcinoma, one with squamous cell carcinoma and two with adenoma featuring high-grade intraepithelial neoplasia. Pathological TNM staging revealed two, seven, five, five and one case(s) in Stages 0, I, II, III and IV, respectively. The median follow-up period was 20 months (interquartile range 22 months), with no withdrawals. The overall and disease-free survival rates were both 95%. The mean Wexner incontinence score and low anterior resection syndrome score recorded 18 months following diverting ileostomy closure were 6.3 ± 3.8 and 27.3 ± 3.6, respectively.

This study has proposed the CSR procedure for the first time, which is a technically feasible, oncologically safe and functionally acceptable procedure for carefully selected patients with rectal tumours located below the dentate line.