[Preoperative levator ani complex volume predicts severe low anterior resection syndrome after intersphincteric resection: development and validation of a nomogram model].

Abstract

Objectives: To investigate the predictive value of preoperative levator ani complex volume measured by magnetic resonance imaging for severe low anterior resection syndrome after intersphincteric resection, and to develop a nomogram prediction model. Methods: This is a retrospective case series study. Clinical data of 134 patients who underwent intersphincteric resection for low rectal cancer at Shaanxi Provincial People's Hospital from January 2016 to December 2023, and 43 patients from the First Affiliated Hospital of Air Force Medical University from January 2021 to December 2022, were retrospectively collected. The cohort included 110 males and 67 females, with an age of (64.7±8.6) years(range:32 to 78 years). Patients from Shaanxi Provincial People's Hospital were randomly divided into a training cohort (94 cases) and an internal validation cohort (40 cases) in a 7∶3 ratio using computer-generated random numbers, while 43 patients from the First Affiliated Hospital of Air Force Medical University served as the external validation cohort. Clinical data were collected, and the volumes of defecation-related muscles, including the levator ani complex, were segmented and normalized using 3D Slicer software based on preoperative magnetic resonance imaging. Severe low anterior resection syndrome was defined as a low anterior resection syndrome score≥30 at six months after stoma closure. Univariate and multivariate Logistic regression analyses were performed to identify independent risk factors for severe low anterior resection syndrome, and a nomogram model was established. Model performance was evaluated by receiver operating characteristic curve, calibration curve, and decision curve analysis. Results: In the training cohort of 94 patients, 41 (43.6%) developed severe low anterior resection syndrome. Multivariate analysis revealed that preoperative chemoradiotherapy (OR=4.901, 95%CI:1.806 to 13.300, P=0.002), total intersphincteric resection (versus partial intersphincteric resection, OR=7.001, 95%CI:1.679 to 29.197, P=0.008), and smaller normalized levator ani complex volume (OR=0.665, 95%CI:0.458 to 0.964, P=0.032) were independent risk factors for postoperative severe low anterior resection syndrome. The nomogram model achieved an area under the receiver operating characteristic curve of 0.778 in the training cohort, which was 0.761 after 1 000 Bootstrap corrections; the area under the curve was 0.759 in the internal validation cohort and 0.707 in the external validation cohort. The calibration curves demonstrated good agreement between predicted and observed probabilities, and decision curve analysis indicated clinical net benefit. Conclusions: Levator ani complex volume, preoperative chemoradiotherapy, and ISR classification are independent predictors of severe low anterior resection syndrome after intersphincteric resection. The nomogram model constructed based on these factors exhibits favorable predictive performance and may assist in preoperative risk assessment.