Lymphatic malformations are collections of malformed, dilated lymphatic channels that do not function correctly. The lymphatic system consists of organs (spleen, thymus, tonsils and adenoids), lymph nodes and thin tubes called lymphatic vessels which carry clear lymphatic fluid. The lymphatic system is an important part of the immune system and functions to remove excess fluid from the tissues of the body.

In lymphatic malformations, the abnormal lymphatic vessels have impaired or slowed transfer of the lymphatic fluid back into the venous system. This causes excess fluid to accumulate and to dilate the abnormal lymphatic channels, resulting in swelling or enlargement of the affected area.

Lymphatic malformations form prior to birth. Although the exact cause of LMs is unknown, they are thought to be caused by errors in the formation and development of the lymphatic vessels during fetal development. Lymphatic malformations are not caused by any known drug, medication or environmental factor that the baby may have been exposed to during the pregnancy. Most LMs are identified at birth or within 2 years of age but some may not be apparent until adolescence or early adulthood.

Lymphatic malformations most commonly occur in the head and neck area (illustration 1), but may involve any area of the body. Although they usually involve only one area (illustration 3), lymphatic malformations can be diffuse or involve multiple body sites (illustration 4). Symptoms and the severity of complications of LMs vary widely and typically depend on the size and the location(s) of the malformation. Regardless of size, lymphatic malformations may cause organ dysfunction, functional disabilities or deformity.

Lymphatic malformations are also sometimes referred to as lymphangiomas or cystic hygromas. However, these terms are outdated and are not recommended to describe these conditions.