Overview — Classification of vascular anomalies

The ISSVA classification subdivides vascular anomalies into vascular tumors and vascular malformations. The group of vascular tumors includes benign, locally aggressive or borderline and malignant vascular tumors, depending on their biological growth pattern. Vascular malformations, on the other hand, are subdivided into simple, combined, major named vessels and associated with other anomalies, depending on the predominant type or types of vessels involved. The classification is summarized in an overview table. A detailed description of the individual vascular anomalies is provided in the following chapters.

Simplified classification of vascular anomalies

Vascular tumors


Locally aggressive or borderline


Vascular malformations

Simple malformations
capillary (CM), venous (VM), lymphatic (LM), arteriovenous (AVM)

Combined malformations
(e.g., CVM, LVM, CLVM, C-AVM, etc.)

Malformations “of major named vessels”
(e.g., marginal vein)

Malformations “associated with other anomalies”
(e.g., Klippel-Trénaunay syndrome, Parkes Weber syndrome, etc.)


Vascular tumors are true vascular masses whose endothelium proliferates, thus showing true solid cell growth of tissue. They mostly affect infants and children and are not necessarily fully developed at birth. In contrast to malformations, they can develop a few weeks to months after birth. In the most common benign variant (infantile hemangioma), after a proliferation phase, they may involute spontaneously between the ages of 1 to 6 years. By far the most common representative of this group is the infantile hemangioma. Other vascular tumors are very rare.

Vascular malformations, on the other hand, are based on variable angiogenic and vasculogenic malformations of vascular maturation (vascular developmental disorders), which are already present at birth but may not be symptomatic. Vascular malformations are thus malformed, dysplastic often tubular or sponge-like vascular spaces that are not solid and contain blood or lymph fluid. They usually show no actual endothelial proliferation and can remain clinically silent for a long time before they are stimulated to enlarge or become clinically manifest in childhood or young adulthood, often as a result of external influences. Then they appear in all parts of the body and involve a variety of very different clinical manifestations. An important distinguishing feature from vascular tumors is also their lack of spontaneous regression. Rather, malformations usually grow proportionally to the growth of the body with the increasing age of the patient and can cause serious complaints due to their progressive enlargement. They consist of either just one developmentally abnormal vessel type, e.g., venous malformation with malformed veins (simple malformation), or a combination of several types of malformed vessels, e.g., a venolymphatic malformation (combined malformation).

If other tissues in addition to the vessels also show abnormal development (usually fatty tissue, muscle, bone), often in the form of hyperplasia, these symptom constellations may form a typical syndrome, e.g., Klippel-Trénaunay syndrome (combined capillary venolymphatic malformation with soft tissue and limb overgrowth) and are referred to as “vascular malformations associated with other anomalies”.