MRI features of lateral lymph nodes predicting lateral local recurrence and prognostic impact of lateral lymph node dissection in low rectal cancer

Objectives: To evaluate MRI features of lateral lymph nodes (LLNs) associated with lateral local recurrence (LLR) and assess the prognostic value of lateral lymph node dissection (LLND) in low rectal cancer. Materials and methods: This retrospective study included consecutive patients with cT3-4 rectal cancer located ≤ 8 cm from the anal verge who underwent radical surgery following neoadjuvant chemoradiotherapy. LLN location, short-axis diameter, and malignant features (internal heterogeneity or irregular borders) were assessed. LLR rates were estimated using Kaplan–Meier analysis and compared with the log-rank test. Cox proportional hazards models identified factors associated with LLR. Results: A total of 878 patients (mean age, 57 ± 12 years; 574 males) were included. The cumulative 5-year LLR rate was 4.2%. Patients with LLNs ≥ 7 mm had higher LLR rates than those with LLNs < 7 mm or no LLNs (17.2% vs. 2.6% vs. 3.1% at 5 years, p < 0.001). Malignant features on pretreatment MRI were associated with higher LLR rates than LLNs without malignant features or no LLNs (28.2% vs. 2.6% vs. 3.1% at 5 years, p < 0.001). In multivariable analysis, malignant features remained independent predictors of LLR (hazard ratio = 9.0 [1.9–43.9], p = 0.006). LLND reduced LLR in patients with internal iliac lymph nodes with malignant features (14.2% vs. 52.9% at 5 years, p = 0.01). Conclusion: Malignant features of LLNs on pretreatment MRI are associated with increased risk of LLR. LLND significantly reduces LLR in patients with internal iliac lymph nodes with malignant features. Key Points: Question The optimal therapeutic approach for rectal cancer patients with abnormal lateral lymph nodes on the staging MRI remains controversial. Findings Malignant features in lateral lymph nodes independently predicted lateral local recurrence, and lateral lymph node dissection reduced recurrence for internal iliac lymph nodes with malignant features. Clinical relevance Identifying malignant features of lateral lymph nodes on pretreatment MRI enables risk stratification for lateral local recurrence and helps guide the need for lateral lymph node dissection, potentially improving oncologic outcomes in patients with low rectal cancer.