Lymphatic Mapping to the Inguinal Region in Patients with Lower Extremity Melanoma Undergoing Radical Inguinal Lymph Node Dissection: A Retrospective Cohort Study

Background/Objectives: The anatomical distribution of inguinal lymph node (ILN) metastases may inform research on the extent of therapeutic dissection for lower-limb melanoma. Methods: Fifty-eight patients undergoing radical inguinal lymph node dissection (rILND) were retrospectively evaluated using five anatomical zones. Zone-specific node counts were reaggregated, and exploratory binary logistic regression assessed multiple-zone involvement. Results: The cohort included 48 clinically node-positive and 10 sentinel lymph node biopsy (SLNB)-positive patients. Among 816 mapped ILNs, 149 were positive. Zone I contained 102/149 positive nodes (68.5%); within-zone positivity was 102/303 (33.7%) in zone I, 27/243 (11.1%) in zone II, 13/190 (6.8%) in zone III, 3/39 (7.7%) in zone IV, and 4/41 (9.8%) in zone V. Five patients had no positive mapped ILNs. Zone I contained the only positive node in 19/20 patients (95.0%) and was the sole involved zone in 32/33 patients with single-zone involvement (97.0%). Twenty patients had multiple-zone involvement. In a two-variable complete-case model (50 patients; 18 events), ≥3 positive ILNs remained associated with multiple-zone involvement (adjusted odds ratio, 34.80; 95% confidence interval, 5.88–206.08), whereas extranodal extension did not. Conclusions: This small, selected cohort provides preliminary pathological evidence of preferential inferior-zone involvement. It does not establish sequential spread or the oncological safety of reduced rILND. External and prospective validation are required.