A simple division of the vascular malformations is made into low-flow and high-flow types. Low-flow malformations involve a single type of blood or lymph vessel, and are known as simple vascular malformations; high-flow malformations involve an artery. There are also malformations that are of mixed-flow involving more than one type of vessel, such as an arteriovenous malformation. Low-flow vascular malformations include capillary malformations, venous malformations, and lymphatic malformations.
Capillary malformation
Capillary malformations involve the capillaries, and are the most common type. They used to refer only to port-wine stains but now include others. Capillary malformations are limited to the superficial layers of the skin but they can thicken, become nodular, and sometimes become disfiguring. It has been proposed that the category of capillary malformations, also called vascular stains, be classified into seven major clinical types including nevus flammeus nuchae also known as nevus simplex, commonly known as stork bite or salmon patch. A capillary malformation is also a feature of the disorder macrocephaly-capillary malformation.
Venous malformation
Venous malformations are typically ill-defined masses, coloured from pale to dark blue. They can affect any tissue in the body. The mass is soft, and easily compressed, and their blue colouring is due to the dilated anomalous involved veins. They are most commonly found in the head and neck. Venous malformations can often extend deeper from their surface appearance, reaching underlying muscle or bone. In the neck they may extend into the lining of the mouth cavity or into the salivary glands. A severe venous malformation can involve the lymph vessels as a lymphaticovenous malformation.
Lymphatic malformation
Lymphatic malformations are congenital, developing from badly-formed lymphatic vessels in early embryonic development. Abnormal development of the lymph vessels results in their failure to connect and drain into the venous system. These lymph vessels can become blocked due to the collection of lymph which forms a cyst as a mass, and are known as lymphangiomas. They can be macrocystic, microcystic, or a combination of the two. Macrocystic have cysts greater than, and microcystic lymphangiomas have cysts that are smaller than. A macrocystic lymphangioma is also known as a cystic hygroma. Cystic hygromas most often occur in the neck where they are known as nuchal hygromas. A severe venous malformation is known as a lymphaticovenous malformation that also involves the lymph vessels.
