Objective To investigate the influencing factors of anastomotic leakage after laparoscopic intersphincter resection (ISR) for extremely low rectal cancer and construction of nomogram prediction model.

Methods The retrospective case‑control study was conducted. The clinicopathological data of 812 patients who underwent laparoscopic ISR for extremely low rectal cancer in the Second Affiliated Hospital of Naval Medical University (Shanghai Changzheng Hospital) from February 2012 to February 2022 were collected. There were 459 males and 353 females, aged (51±11)years. Observation indicators: (1) surgical situations; (2) follow‑up; (3) influencing factors of postoperative anastomotic leakage; (4) construction and evaluation of nomogram prediction model for postoperative anastomotic leakage. Measurement data with normal distribution were represented as Mean±SD, and measurement data with skewed distribution were represented as M(range). Count data were described as absolute numbers. The COX proportional hazard model was used for univariate and multivariate analyses. The R software(3.5.1 version) was used to construct nomogram prediction model. The receiver operating characteristic (ROC) curve was drawn and the area under curve (AUC) was used to evaluate the efficacy of the nomogram prediction model. The Bootstrap method was used for internal verification and to calculate the average consistency index (C-index).

Results (1) Surgical situations. All 812 patients underwent laparoscopic ISR for extremely low rectal cancer, including 388 cases undergoing partial ISR, 218 cases undergoing subtotal ISR and 206 cases undergoing complete ISR. All 812 patients underwent ileal protective ostomy, and there were 306 cases with double anastomosis and 203 cases with left colic artery preserved, respectively. The operation time and volume of intraoperative blood loss of 812 patients was (179±33)minutes and (33±13)mL, respectively. (2) Follow‑up. All 812 patients were followed up for (13.5±0.9)months. Of the 812 patients, there were 62 cases with postoperative anastomotic leakage and the healing time of these cases was (33±6)days. (3) Influencing factors of postoperative anastomotic leakage. Results of multivariate analysis showed that male, neoadjuvant chemoradiotherapy, failure of reser-ving left colic artery were independent risk factors of anastomotic leakage after laparoscopic ISR for extremely low rectal cancer (hazard ratio=5.98, 4.00, 16.26, 95% confidence interval as 1.66-24.12, 1.30-12.42, 3.00-90.89, P<0.05). (4) Construction and evaluation of nomogram prediction model for postoperative anastomotic leakage. According to the results of multivariate analysis, male, neoadju-vant chemoradiotherapy and failure of reserving left colic artery were used to construct the nomogram prediction model for anastomotic leakage after laparoscopic ISR for extremely low rectal cancer, and the score of these indexes in the nomogram prediction model was 50, 49, 93, respectively. The total score of these index corresponded to the incidence rate of anastomotic leakage. Results of ROC curve showed that the AUC of nomogram prediction model of anastomotic leakage after laparoscopic ISR for extremely low rectal cancer was 0.87 (95% confidence interval as 0.80-0.93, P<0.05), with sensi-tivity and specificity 0.96 and 0.60, respectively. Results of internal verification showed that the C-index of nomogram prediction model was 0.87.

Conclusion Male, neoadjuvant chemoradiotherapy, failure of reserving left colic artery are independent risk factors of anastomotic leakage after laparo-scopic ISR for extremely low rectal cancer, and the nomogram prediction model based on these indexes can predict the incidence rate of postoperative anastomotic leakage.