Congenital pulmonary lymphangiectasia (CPL) is a rare developmental disorder that affects the lungs. It is present from birth and usually becomes apparent in the first few days of life with respiratory failure. It sometimes is apparent before birth with non-immune hydrops fetalis and pleural effusion (fluid in the lung). Infants with CPL often develop severe, potentially life-threatening, respiratory distress shortly after birth. They may also develop cyanosis caused by low oxygen levels in the blood, which causes the skin to have a bluish tint. Symptoms are due to abnormally wide (dilated) lymphatic vessels within the lungs. These vessels drain a fluid called lymph from different areas of the body. They are an important part of the lymphatic system, which helps the immune system protect the body against infection and disease. The underlying cause of CPL is unknown. It can occur as a primary or secondary disorder (due to another underlying condition). Primary CPL occurs as an isolated defect or as part of a generalized form of lymphatic disease affecting the whole body. Secondary CPL can occur due to a variety of heart abnormalities or lymphatic obstruction. Some cases of CPL have been associated with genetic disorders.