Background: The knowledge of where does excess tissue fluid accumulate in obstructive lymphedema is indispensable for rational physical therapy. However, it has so far been limited to that obtained from lymphoscintigraphic, ultrasonographic, and MR images. None of these modalities provide composite pictures of dilated lymphatics and expanded tissue space in dermis, subcutis, and muscles. So far, only anatomical dissection and histological processing of biopsy material can visualize the tissue lymphatic network and the sites of accumulation of the excess of mobile tissue fluid.
Methods and results: We visualized the "tissue fluid and lymph" space in skin and subcutaneous tissue of foot, calf, and thigh in various stages of lymphedema in specimens obtained during lymphatic microsurgical procedures or tissue debulking, using special staining techniques. The volume of accumulated fluid was calculated from the densitometric data of stained tissue sections. We found that lymph was present only in the subepidermal lymphatics, whereas the collecting trunks were obliterated in most cases. Mobile tissue fluid accumulated in the spontaneously formed spaces in the subcutaneous tissue, around small veins and above and underneath muscular fascia. Deformation of subcutaneous tissue by free fluid led to formation of interconnecting channels. The volume of subcutaneous free fluid ranged around 50% of total tissue volume and there were no significant differences in various stages of lymphedema. This could be explained by the presence of thick layers of subcutaneous fat tissue even in the most advanced stage of lymphedema.
Conclusions: In lymphedema caused by obliteration of collecting trunks, lymph is present only in the subepidermal lymphatics, whereas the bulk of stagnant tissue fluid accumulates in the subcutaneous tissue and above and beneath muscular fascia. These findings should be useful for designing pneumatic devices for limb massage as well as for rational manual lymphatic drainage in terms of sites of massage and level of applied external pressures.