Magnetic Resonance Imaging-Based Scoring Systems for Selective Lateral Lymph Node Dissection in Locally Advanced Low Rectal Cancer After Neoadjuvant Chemoradiotherapy

Abstract

Purpose To develop scoring systems to predict the need for selective lateral lymph node dissection (LLND) alongside total mesorectal excision (TME) in patients with locally advanced low rectal cancer after neoadjuvant chemoradiotherapy (nCRT), focusing on lateral local recurrence (LLR) and lateral lymph node (LLN) metastasis. Materials and Methods This retrospective study included 607 patients with mrT3/T4 rectal cancer located within 8 cm of the anal verge who underwent nCRT and TME. A development group was used to develop a scoring system predicting the necessity of LLND using logistic regression analysis, incorporating primary tumor and LLN features observed on rectal magnetic resonance imaging (MRI). External validation was conducted by comparing the model with established criteria and in an independent group of 144 patients. We also analyzed risk factors for recurrence and residual LLNs after LLND. Results Model 1 included pretreatment LLN size and extramural venous invasion (EMVI). Model 2 incorporated pretreatment internal iliac and obturator lymph node sizes, EMVI, and nonresponsive LLN on restaging MRI. In the development group, Models 1 and 2 exhibited high performance (area under the curve [AUC] = 0.92 and 0.90, respectively). Compared with the established criterion, which focused solely on nonresponsive LLNs on restaging MRI, Model 1 demonstrated the highest sensitivity, while Model 2 showed moderate sensitivity and specificity. Among patients who underwent LLND, the distal internal iliac compartment had more residual lymph nodes than other compartments (p = 0.02). Conclusion Scoring systems utilizing LLN features and EMVI on MRI could aid in decision-making for selective LLND following nCRT in locally advanced low rectal cancer.