Vascular malformations are present at birth. They never proliferate and never involute. Instead, they increase in size steadily as the patient grows and they do so by an increase in the size of the vessels those make up the malformation. Vascular malformations are further classified according to the type of vessel that makes up the lesion.

The major types of vascular malformations are:

• Venous
• Venular (port wine stains)
• Arterio-venous
• Lymphatic malformations

Mixed Malformations

• Venous Lymphatic capillary (Klippell Trenauney Syndrome: KTS)
• Arterio- venous capillary malformation (Parkes Weber Syndrome)

Port wine stains

Port wine stains are the most common vascular malformations. They occur in about 1 out of every 1,000 people. A port wine stain is an area of skin in which the small veins just under the surface of the skin are dilated. This dilatation will increase the amount of blood in the veins and this will impart a reddish stain to the skin. The underlying cause of the dilatation of these vessels is believed to be an absence of innervations (nerve connection) to the muscle wall surrounding the small veins. Since the embryo develops segmentally (in parts, with each part developing independently), usually only one or two segments may be involved, occasionally, the condition can be more widespread. The absence of nerve connection will result in a muscle wall that has no tone (function) and this in turn will cause these vessels to dilate, hence the increase in blood volume in these vessels and hence the discoloration. Since the blood circulation is dynamic, the intensity of color will vary according to the volume of blood present within the vessels.

Although we group all port wine stains together, there are clearly different types of port wine stain. To date, no sub classification has been proposed. Some port wine stains are darker than others. This is probably due to the density of affected vessels. Some are confluent whereas others are geographic in their distribution.

The intensity of color will vary as the blood flow varies. When the patient is hot or angry, the flow of oxygenated blood will impart a more intense, reddish discoloration to the lesion. The process of aging will affect the port wine stain. A slow steady dilatation of the vessels will result in an increase intensity of color and as the amount of elastin and collagen diminishes, the port wine stain will thicken. Some will form nodules called cobblestones which can get quite large if left untreated. The age of onset of these cobblestones varies from the mid 20's to the 60's. It must be stressed that cobblestone formation is not inevitable. In an even smaller percentage of patients, there will be tissue overgrowth or thickening of the soft tissues within the affected area. The exact cause of this is unknown but it appears to be a segmental growth signal abnormality.

Port wine stains may be associated with syndromes, the most important of which is Sturge Weber Syndrome. This condition is an association of a portwine stain, ocular (eye) involvement and involvement of the meninges (the membranes that cover the brain). In its worst form, this syndrome can cause seizures, mental retardation and visual loss. This is NOT inevitable and the reader should be referred to a site that specializes in Sturge Weber Syndrome. Many patients with Sturge Weber Syndrome have very mild disease and live completely normal lives. For more information on Sturge Weber Syndrome. http://www.sturge-weber.org

Eye involvement without brain involvement does occur and is more commonly seen if there is skin involvement above and below the eye. This is not Sturge Weber Syndrome. These children should be seen by an ophthalmologist in order to correctly diagnose whether or not there is eye involvement and if so, to treat and prevent complications.

Venous Malformations

These lesions are made up of a plexus of dilated veins. Venous malformations can be localized or diffuse, superficial or deep.

Certain anatomical sites are frequently involved; these include mouth, lips, tongue cheek, side of the face and neck. If the venous malformation is superficial, the skin and/or mucosa has a bluish hue. Since venous malformations are essentially on the venous side of the circulation, they will enlarge when the area involved is in the dependant position. As the patient gets older, the malformation will expand and if the overlying skin or mucosa is very thin, this can result in bleeding. Venous malformations may be multifocal and they have a spongy consistency to palpation.

The underlying cause of venous malformations is probably the same as port wine stains except that the level of involvement is at a deeper level.

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.

Lymphatic malformations are also known as Lymphangiomas or Cystic Hygromas. Lymphatic malformations 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.