An arterio-venous malformation is a vascular lesion made up of small vessels linking the arterial side of the circulation to the venous side. These may be widespread, diffuse lesions or they may be localized, focal lesions. The overlying skin may be involved and in these cases, there is a pinkish hue. As with all other vascular malformations, arterio-venous malformations are always present at birth although they may only become evident at a later stage. Slow steady expansion will be seen and the supplying arteries and draining veins will also increase in size as the malformation enlarges. These lesions are fairly firm to palpation and are frequently surrounded by large dilated vessels. They usually do not expand when in a dependant position.