Lymphatic flow velocity is a predictor of functional lymphatic vessels for lymphaticovenous anastomosis

Background: Indocyanine green (ICG) lymphography is widely used to localize functional lymphatic vessels for lymphaticovenous anastomosis (LVA); however, flow velocity is rarely assessed. We aimed to evaluate the correlation between lymphatic flow velocity and the presence of functional lymphatic vessels. Methods: Data of a total of 924 lymphatic vessels from 273 lymphedema patients who underwent LVA between July 2018 and December 2020 were retrospectively reviewed. Lymph flow velocity was defined by considering the most proximal anatomic location enhanced by ICG at 30 min after injection and categorized into four groups; grade 1 (foot or hand), grade 2 (below knee or elbow), grade 3 (at/above knee or eblow), or grade 4 (axilla or groin). The presence of functional lymphatic vessels, which showed lymphatic fluid flow when the vessels were cut for anastomosis, was compared between the four groups. Results: A higher rate of functional lymphatic vessels was observed among lymphatic vessels with grade 3 or 4 flow velocity compared with those with grade 1 or 2 flow velocity (67.5% vs. 44.5%; p < 0.001). These findings were consistent with the observations for lymphatic vessels with a non-linear pattern in ICG lymphography (59.4% vs. 26.5%; p < 0.001). The rate of completion of LVA at surgical sites in extremities with grade 3 or 4 flow velocity was 88.1% compared with 65.8% in extremities with grade 1 or 2 velocity (p < 0.001). Conclusions: Lymph flow velocity grading can be a simple and easy adjunctive method to determine indication for LVA in extremities with lymphedema.