Objective:To observe the drainage effects of the venous and arterial perivascular and adventitial connective tissues(PACT)on edema of lower limbs in mice model, and to provide a new understanding of the drainage for the elderly lower extremity edema.Methods:Different doses of fluorescent sodium(FluoNa)were injected into the venous and arterial perivascular connective tissues in the feet and ankles of the lower limbs to create a model of lower extremity edema in mice.Then, at the level of the femoral artery and vein sheath, a stereoscopic fluorescence microscope was used to observe and record the drainage effect of vascular PACT pathways on the edema.Results:By tracking the diffusion and flowing of FluoNa in the interstitial space of ankle and foot, we found that(1)in addition to the local diffusion at the injection site, FluoNa can also flow along the venous and arterial PACT and the interstitial spaces between the corresponding vein and artery.(2)The flowing process along the vascular adventitia included transmission along the vascular long axis, and the long axis-perpendicular diffusion into the vascular peripheral tissue.(3)When low-dose and high-dose FluoNa were administered into the venous adventitia of the lower extremities, the venous PACT imaging was observed.(4)When low-dose and high-dose FluoNa were administered into the arterial adventitia of the lower extremities, the arterial PACT imaging was observed; (5)When low-dose and high-dose of FluoNa were administered into the near the arteriovenous-accompanying blood vessels, not only the venous PACT pathway and the arterial PACT pathway are imaged, but also the interstitial space between the pathway of the accompanying vein and artery was also visualized at the same time; (6)Histological analysis showed that the tissues stained by FluoNa were the venous and arterial adventitia and perivascular connective tissues.Conclusions:The interstitial fluid in lower extremity tissue edema can not only be drained by the venous or arterial PACT pathway, but also be drained through the interstitial space between the accompanying vein and artery when a large amount of the interstitial fluid accumulates.