Endothelioma of the soft palate: a, dilated lymph space; b, endothelial cells with beginning cystic formation; c, completely formed cyst. (Volkmann.)
G. Angiosarcoma.
—Angiosarcoma is a sarcoma arising from the adventitia of the bloodvessels. It is characterized by its extraordinary vascularity, the ease with which hemorrhages into the structure of the tumor take place, and the frequency of pigmentation. Peritheliomas constitute a subvariety, met with especially in the kidneys, the bones, and the skin, and originate in the perithelial cells between the capillaries and the perivascular lymph spaces. They are more vascular than the angiosarcomas. The latter are common in the liver. In many cases the cells of these tumors simulate the columnar epithelium of adenocarcinoma. (See [Plate XVIII, Fig. 1].)
H. Cylindroma.
—This is a term applied to tumors of the angiosarcomatous type in which hyaline changes have occurred, so that along the vessels appear cylindrical masses of altered cells. Similar appearances are noted in certain endotheliomas and are due to the same hyaline degeneration.
I. Melanosarcoma (better known as Melanoma).
—This refers to the deposition of pigment, rather than to type or shape of cell, the distinguishing feature of these growths being the presence both in the cells and in the intercellular substance of a variable quantity of blackish pigment. Of all the forms the melanotic growths are considered the most malignant. They invariably recur after removal, lead to secondary deposits at long distances, and present the most intractable and incurable forms of cancer. Deposition of pigment in carcinomas is most rare, if ever met with, and the growths of melanotic type should be relegated entirely to the class under consideration. The tumors most often develop from pigmented nevi of the skin, though primary melanoma of the deeper parts of the body is known. These will be treated more fully in the chapter on the Skin. (See [Plate XX].)
This name has been variously applied by different writers to different growths. In order to avoid confusion it would be well, in using it, to be definite.
General Characteristics of Sarcomas and Endotheliomas.
—The vascular supply of sarcomas varies within wide limits. In nearly all instances it is of capillary character, the blood circulating rather through vessels without well-marked walls. While large vessels may be found about and in the periphery of these tumors, distinct vascular structure is usually absent from the more internal portions, which will explain the frequency of hemorrhage, its persistency after operation, and the ease with which large extravasations occur. True hematocele may thus take place within sarcomatous tumors, with the usual later cystic alterations, and thus in one way we have the condition known as cystosarcoma.