MRI-based scoring systems for selective lateral lymph node dissection in locally advanced low rectal cancer after neoadjuvant chemoradiotherapy.

OBJECTIVES

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 MRI. External validation was performed 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. Model 3 focused solely on nonresponsive LLN on restaging MRI. In the development group, Models 1 and 2 exhibited better performance (area under the curve (AUC) = 0.92 and 0.90, respectively) than Model 3 (AUC = 0.79), consistent with the validation group. 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 might aid in decision-making for selective LLND following nCRT in locally advanced low rectal cancer.

KEY POINTS

Question The criteria for when additional lateral lymph node dissection (LLND) may benefit in locally advanced low rectal cancer have not yet been definitively established. Findings Scoring systems (Model 1, 2) based on preoperative MRI utilize lateral lymph node (LLN) size and extramural venous invasion to predict the necessity of LLND. Clinical relevance The selective LLND along with total mesorectal excision aids in managing LLN metastasis and lateral local recurrence in locally advanced low rectal cancer after neoadjuvant chemoradiotherapy. The imaging-based scoring systems may guide clinical decision-making for selective LLND.