Lymphedema: anatomy, physiology and pathogenesis.

The authors review the current understanding of lymphatic anatomy and physiology, and the pathophysiology of lymphedema. The skin lymphatic system consists of the initial lymphatics, which converge into lymphatic precollectors, collectors and lymphatic ducts; these in turn convey the lymph to the regional lymph nodes. Interstitial fluid and particles enter the initial lymphatics through interendothelial openings and by vesicular transport. Lymphatic uptake is enhanced by external compression. Lymphatic transport depends greatly on contraction of lymphangions, which generate the suction force that promotes absorption of interstitial fluid and expels lymph to collecting ducts. In lymphedema, various types of congenital and acquired abnormalities of lymphatic vessels and lymph nodes have been observed. These often lead to lymphatic hypertension, valvular insufficiency and lymphostasis. Accumulation of interstitial and lymphatic fluid within the skin and subcutaneous tissue stimulates fibroblasts, keratinocytes and adipocytes eventuating in the deposition of collagen and glycosaminoglycans within the skin and subcutaneous tissue together with skin hypertrophy and destruction of elastic fibers.