Near-Infrared Fluorescence Imaging Directly Visualizes Lymphatic Drainage Pathways and Connections between Superficial and Deep Lymphatic Systems in the Mouse Hindlimb

Since lymphedema rarely develops in the mouse hindlimb, the underlying mechanisms remain unclear. We herein investigated the resolution of chronic hindlimb lymphedema in mice using a Near-Infrared Fluorescence (NIRF) imaging system. Nineteen 7-28-week-old BALB/c male and female mice were injected with two dyes for lymphography and dissection. Lymphadenectomy was performed on six male mice to completely obstruct lymph flow in the hindlimb. Edematous changes in both hindlimbs were compared until 60 days after surgery. The NIRF imaging system detected three lymphatic collecting systems in the mouse hindlimb: superficial lateral, superficial medial, and deep medial. It also showed connections between the superficial and deep lymphatic systems in the inguinal region. Lymphadenectomy of the iliac, inguinal, and popliteal lymph nodes caused edematous changes. However, lymph flow in these operated areas restarted within 60 days and the severity of lymphedema appeared to be low. NIRF imaging showed that the deep medial system and a connection between the superficial and deep lymphatic systems in the inguinal region drain lymph from the hindlimb. This is the one reasons why lymphedema does not develop in the mouse hindlimb. The stable obstruction of lymph flow in these three systems is desired to develop chronic lymphedema.