Preoperative Magnetic Resonance Imaging Results Are Concordant with Pathology Staging in Rectal Cancer

Background and Objectives: Magnetic resonance imaging (MRI) is the gold standard for rectal cancer staging; however, its reliability after neoadjuvant therapy (NAT) remains controversial due to treatment-induced tissue changes. This study aimed to compare preoperative MRI findings with postoperative pathologic results in rectal cancer patients following NAT and to assess MRI reliability across clinical subgroups. Materials and Methods: This single-center retrospective study included 47 adult patients with locally advanced rectal adenocarcinoma who received NAT followed by elective rectal resection, with preoperative pelvic MRI and postoperative pathology results. Clinical features, MRI (T stage, N stage, and circumferential resection margin [CRM]), and pathologic staging were recorded. The endpoints were defined as concordance (via kappa coefficients) and predictive performance (via ROC analysis). Results: Among 47 patients (mean age 63.5 ± 9.4 years; 80.9% male), MRI demonstrated slight concordance with pathology for the T stage (kappa = 0.178, p = 0.028) and moderate concordance with the N stage (kappa = 0.489, p < 0.001), but not for CRM (p = 0.154). Subgroup analyses revealed significant concordance for N stage across most subgroups, with lower rectal tumors showing significant agreement for all three parameters. ROC analysis demonstrated significant predictive value for the N stage (AUC = 0.776, p = 0.002) with 88.6% specificity, while the T stage and CRM showed non-significant discriminatory performance. Conclusions: Post-NAT MRI demonstrates moderate reliability relative to pathology, particularly for N staging, and may have even better utility in specific subgroups stratified for sex, NAT type, and tumor site.