COURSES

The classification of vascular malformations was, at one time, mostly dependent upon anatomical site and region. During the past two decades, this anatomical classification became replaced by a better understanding of endothelium and the resultant biological classification was published (Mulliken J B & Young A E, 1988, Vascular Birthmarks: Hemangiomas and Malformations, W B Saunders Company) (Ryan T J and Cherry G W, Vascular Birthmarks: Pathogenesis and Management, 1987, Oxford University Press). The classification broadly reflects: 1. Those birthmarks due to the proliferation and later involution of endothelium and 2. Those birthmarks in which there is a disturbance of the relationship between the endothelium of the vessel and the tissue it supplies, mostly resulting in dilation of the vasculature and atrophy of the tissue supplied. An atrophy of the capillary bed often favours more proximal connections between the arterial and venous system. Such shunting can affect the dynamics of intravascular pressure and flow and lead to an increase in the size of the malformations. While a biological classification enhances our understanding, descriptions of the anatomical distribution of the birthmark helps with its classification of various sub types of vascular malformation affecting the viscera or bony tissues.