Validation of Magnetic Resonance Imaging-Based Diagnostic Criteria for Lateral Lymph Node Dissection in Rectal Cancer: A Multicenter Prospective Study.

Objectives: Optimal indications for lateral lymph node dissection in patients with rectal cancer have not yet been established. To address this, we previously proposed magnetic resonance imaging-based size criteria that combine long- and short-axis measurements. However, the initial study derived criteria based on an analysis with knowledge of histopathological outcomes. Therefore, this study aimed to prospectively validate the clinical utility of these magnetic resonance imaging-based criteria. Methods: We conducted a prospective multicenter validation study including 125 patients with rectal cancer who underwent radical surgery with lateral lymph node dissection. Two independent reviewers who were blinded to the clinical and pathological data evaluated 250 lateral pelvic regions using pretreatment magnetic resonance imaging. Interobserver agreement was assessed using weighted kappa statistics. The need for lateral lymph node dissection was evaluated using predefined size-based criteria and compared with the histopathological outcomes. Results: Among the 250 lateral regions evaluated, 206 were dissected, and 29 were histopathologically positive for lateral lymph node metastases. Two reviewers independently assessed whether lateral lymph node dissection was required or could be omitted in 250 regions based on the criteria, and the interobserver agreement was good (weighted kappa = 0.671). The proposed criteria achieved sensitivities of 86.2% and 82.8% and specificities of 57.1% and 52.0% for reviewers 1 and 2, respectively. Conclusion: This validation study demonstrated that our magnetic resonance imaging-based size criteria are clinically applicable and effective for the preoperative diagnosis of lateral lymph node metastases.