A combined vascular malformation involves two or more types of vessel abnormalities. Any of the four types of lesions (capillary, venous, lymphatic, or arteriovenous) may be combined (illustration 1).

Combined malformations may be associated with undergrowth or overgrowth of the bones and soft tissues (skin, fat and muscle). 

Most combined malformations involve limbs, but they can involve any area of the body. While the precise cause of these lesions is not always known, they develop early in embryonic life and are thought to be caused by an error in the formation of the circulatory system (blood vessels and lymphatic channels) in a particular anatomical area.