Lymphatic mapping to the inguinal region in patients with lower extremity melanoma undergoing radical inguinal lymph node dissection: A retrospective cohort study.

e21567 Background: Radical inguinal lymph node dissection (rILND) is the standard procedure for malignant melanoma (MM) patients with clinically positive inguinal lymph nodes (ILNs), but its precise anatomical boundaries remain unclear. This study aims to investigate the lymphatic drainage pattern of inguinal lymph nodes in lower limb MM using definitive pathological evidence. Methods: A total of 58 patients with lower limb MM who underwent rILND were included in this study. The inguinal ILNs were categorized into five anatomical zones for pathological examination. Statistical analysis was performed using the Chi-squared test, binomial logistic regression, and Kaplan-Meier survival analysis. Results: The distribution of ILNs in the inguinal basin exhibited a stepwise pattern, with a high density in the inferior zone. Positive ILNs were predominantly found in zone I (68.5%), followed by zone II (18.1%) and zone III (8.7%). Notably, the first-station and single-positive ILNs were overwhelmingly located in zone I (95% and 94.9%, respectively) . Extranodal extension (ENE) and the presence of three or more positive nodes were identified as significant prognostic factors for multiple-zone metastasis. Conclusions: This study provides a detailed lymphatic drainage map for the inguinal basin in patients with lower limb MM, demonstrating that the inferior zone is the first site of metastasis in a stepwise distribution pattern. Based on these definitive pathological findings, a modified approach to rILND may be considered for patients with lower limb MM. Lymph node distribution across different zones. Positive LNs (mean±SD) All removed LNs (mean±SD) Total 2.58±2.51 14.07±4.56 Zone I 1.76±1.39 5.22±3.29 Zone II 0.47±1.01 4.19±2.34 Zone III 0.22±0.75 3.28±2.19 Zone IV 0.05±0.22 0.67±0.99 Zone V 0.07±0.26 0.71±0.94 LN: lymph node. Zone I: inferior zone; Zone II: superior lateral zone; Zone III: superior medial zone; Zone IV: deep zone; Zone V: Cloquet’s node.