Ultra-High-Frequency Ultrasound–Detected Lymphatic Structural Transition Points Are Located Central to Early Dermal Backflow Transition Points on Indocyanine Green Lymphography

Background In lymphaticovenular anastomosis (LVA), discrepancies between functional assessment of lymphatic flow using indocyanine green (ICG) lymphography and structural evaluation using ultrasound remain a challenge. This study aimed to clarify the spatial relationship between the early dermal backflow transition point (eDBF-TP) identified by ICG and lymphatic structural transition points (LSTPs) detected by ultra-high-frequency ultrasound (UHFUS).Methods This prospective observational study included 60 sites in patients with secondary limb lymphedema. After identifying eDBF-TP using ICG lymphography, UHFUS was performed within ±50 mm from the reference point (0 mm). LSTPs were defined as obstruction, luminal narrowing, or tortuous segments, and their spatial relationships relative to eDBF-TP were analyzed.Results LSTPs were identified in 93.3% of sites and were predominantly located central to the eDBF-TP. Obstruction and severe narrowing were mainly found centrally, whereas tortuous segments were more frequently observed peripherally. Only 35% of LSTPs were located within ±5 mm of the eDBF-TP, indicating a spatial discrepancy between functional and structural abnormalities. Confluence points were consistently located peripheral to LSTPs. Intraoperatively, dilated lymphatic vessels peripheral to LSTPs were suitable for anastomosis in all cases and demonstrated favorable washout flow.Conclusions Functional lymphatic failure may occur peripheral to structural abnormalities. For LVA, selecting dilated lymphatic vessels located peripheral to structural transition points-rather than directly at the eDBF-TP-may represent a rational and effective strategy for determining optimal incision sites.