What causes lymphedema?

LymphaticObstruction: The most common cause of lymphedema is removal of lymph nodes (lns) as part of breast cancer surgery. When combined with radiation therapy, lymphedema may develop in as many as 25% of patients. Over the past decade, a less invasive technique for ln evaluation, called sentinel ln biopsy, has reduced this rate down to less than 5%.

Primary vs secondary: As dr. Rosen said, the major cause of lymphedema is lymphatic obstruction. This is most commonly due to cancer and its treatment: surgery and/or radiation. This is secondary lymphedema because there is an identifiable cause. The other type of lymphedema is primary. This means that there is no cause we can identify and is usually because part of your lymph drainage system doesn't form or fails.

Simple anatomy: Lymphedema occurs when there is a compromise of the lymphatic circulation. This third circulation (arteries, veins) carries things too thick to be safely carried in arteries and veins like bacteria eaten by white cells and digested food. It is propelled along by normal body movements but contains a thick material called lymph. Blockage causes it to back up causing soft tissues/skin deformity.