There are two ways of fluid return in normal human tissues, as follows: 1. through the veins. 2. in the tissue interstitial fluid, which is returned through the lymphatic vessels and finally injected into the veins. When the lymphatic vessels are blocked, the fluid accumulated in the tissues cannot complete the normal lymphatic return, so it will cause tissue edema, and the fluid leaking from the veins keeps gradually increasing from the veins, then the lymphedema will intensify, and the lymphatic vessels will be further occluded when the pressure in the tissues increases, thus forming a vicious circle, making the blocked capillary lymphatic vessels more serious, more extensive, and more edema.