For nearly all types of tumors of the skin it is possible to make the correct diagnosis and to establish the prognosis from the histologic examination of a specimen. Such relative accuracy of results of laboratory procedure, however, does not hold true for tumors of the blood vessels. Examples are occasionally seen of tumors which histologically show great cellular activity but which follow a benign course. More often, however, one encounters vascular tumors which seem histologically benign but which in time metastasize and eventually cause death.
This frequent discrepancy between the histologic changes and the clinical course has made it difficult to establish an acceptable classification of tumors of the blood vessels. A simple grouping,1 based on a consideration of both clinical and histologic features, would divide such tumors into (1) hemangiomas, which are benign clinically and histologically; (2) hemangioendotheliomas, in which