Indications for Lateral Pelvic Lymph Node Dissection Based on Magnetic Resonance Imaging Before and After Preoperative Chemoradiotherapy in Patients with Advanced Low-Rectal Cancer.

Background: We assessed the magnetic resonance imaging (MRI) findings of lateral pelvic lymph node (LPLN) metastasis in patients with advanced low-rectal cancer treated with preoperative chemoradiotherapy (CRT) and LPLN dissection (LPLD) for clinically suspected LPLN metastasis. Our aim was to identify the optimal indications for LPLD.

Methods: The study population consisted of 77 patients with advanced low-rectal cancer who underwent LPLD for clinically suspicious LPLN metastasis after preoperative CRT. MRI findings before/after CRT, clinical factors, and LPLN metastasis were evaluated.

Results: LPLN metastasis was confirmed in 31 patients (40.3 %). Metastasis was significantly higher in patients with LPLNs with a short-axis diameter ≥8 mm than in patients with LPLNs with a short-axis diameter <8 mm before CRT (75 vs. 20 %, P < 0.0001). LPLN metastasis was also significantly higher in patients with LPLNs with a short-axis diameter >5 mm than in patients with LPLNs with a short-axis diameter ≤5 mm after CRT (75 vs. 20 %, P < 0.0001). Multivariate analysis showed the independent association of female sex [P = 0.0192; odds ratio (OR) 5.616; 95 % confidence interval (CI) 1.315-28.942], pre-CRT short-axis diameter of the LPLN ≥8 mm (P = 0.0047; OR 9.188; 95 % CI 1.948-54.366), and CRT without induction systemic chemotherapy (P = 0.0285; OR 9.235; 95 % CI 1.241-106.947) with LPLN metastasis.

Conclusions: MRI before CRT is useful to predict LPLN metastasis and to determine the indications for LPLD.