ObjectiveAlthough collateral lymphatic vessels are known to develop in patients with lymphedema, little is known about their significance. In this study, we investigated truncal collateral lymphatic drainage pathways in patients with lower limb lymphedema using indocyanine green (ICG) lymphography.MethodsThe ICG fluorescence images and clinical characteristics of 80 consecutive patients (160 lower limbs) with secondary leg lymphedema who underwent ICG lymphography between September 2020 and September 2022 were retrospectively reviewed.ResultsSeven patients were identified to have a truncal collateral lymphatic drainage pathway starting in the lateral abdomen and running in the direction of the ipsilateral axillary lymph nodes. These patients had particularly severe symptoms of lymphedema around the thigh or abdominal region or had genital lymphedema.ConclusionsA truncal collateral lymphatic drainage pathway may be associated with severe lower limb lymphedema, particularly if involving the genitals.