Development and validation of a multiparametric magnetic resonance imaging-based nomogram for predicting feasibility of sphincter-preserving surgery in mid-low rectal cancer

ObjectiveAlthough distance from the inferior tumor edge to the anal verge (DTAV) is a key predictor for sphincter-preserving surgery (SPS) in mid-low rectal cancer, its utility is limited in the “decision-gray zone” (DTAV, 3−8 cm). Therefore, this study aimed to develop and validate a multiparametric magnetic resonance imaging-based nomogram for individualized preoperative prediction of SPS feasibility. MethodsThis dual-center retrospective study included 335 patients with rectal adenocarcinoma (DTAV 3−8 cm). Patients were divided into training (n=263) and external validation (n=72) cohorts, and predictors were identified using multivariate logistic regression analysis. Model discrimination was assessed using area under the receiver operating curve (AUC) and calibration via the Hosmer-Lemeshow test. Subgroup analyses were performed across DTAV strata. ResultsFour independent predictors were identified: larger DTAV [odds ratio (OR) =5.00, P<0.001)], larger pubococcygeal overlap distance (PCOD) (OR=1.08, P=0.001), transverse diameter of mesorectal fat (TMS) (OR=1.07, P=0.017), and subcutaneous adipose tissue thickness (SAT) (OR=0.94, P=0.016). The Sphincter Preservation Assessment in Rectal Cancer (SPARC) nomogram achieved an AUC of 0.928 [95% confidence interval (95% CI): 0.890−0.956] in the training cohort, outperforming DTAV alone (AUC=0.884, P=0.031) and maintaining an AUC of 0.916 (95% CI: 0.827−0.969) in external validation. Subgroup analysis showed notably improved predictions in the 5−8 cm DTAV subgroup. Decision curve analysis demonstrated a pronounced net clinical benefit across a wide range of threshold probabilities. Interobserver agreement was excellent (intraclass correlation coefficient, 0.890−0.997). ConclusionsThe SPARC nomogram reliably predicted SPS feasibility by integrating tumor location with pelvic anatomy and fat distribution. This provides valuable and evidence-based preoperative guidance, especially within the DTAV 3−8 cm gray zone.