Lymphatic malformations (previously known as Lymphangiomas or Cystic Hygromas), occur when the flow of lymph across a region slows down. It is believed that the mechanism that transports the lymph is defective. Lymph will accumulate within these defective vessels and this presents as a mass. The mass will vary in size depending on the area of involvement. The mass is usually firm and is not compressible. If there is skin involvement, small vesicles can be found on the surface. If mucosa is involved, the same fluid-filled vesicles can be seen. Since the flow of lymph can fluctuate, any condition that increases the amount of lymph will cause an increase in the size of the lesion. These include infections (usually viral), hormonal changes (pregnancy and puberty) and trauma. Lymphatic malformations can be made up of large cysts (macrocystic) or small cysts (microcystic).
The natural history of lymphatic malformations is relentless expansion with advancing age. Some will enlarge more rapidly than others. These we call high grade lesions. Low grade lesions are less active, present later in life and expand much more slowly. The physiologic process that differentiates these 2 groups is unknown.