According to the Mayo Clinic, lymphedema is caused by lymph vessels being unable to drain lymph fluid sufficiently, typically from a leg or arm. Primary lymphedema occurs on its own, whereas secondary lymphedema is the result of another disease or condition. Secondary lymphedema is much more common.
According to the Mayo Clinic, the causes of secondary lymphedema may include surgery, radiation treatment for cancer, cancer and infection. Lymphedema may result from lymph nodes or lymph vessels being cut or removed. Radiation can cause inflammation of lymph nodes or lymph vessels, restricting the flow of lymph fluid. Cancer may cause lymphedema in the event that cancer cells block lymphatic vessels. Primary lymphedema is a rare, inherited condition that happens most commonly in women.