TUMORS. 



375 



Angiosarcomata are tumors in which a new formation of blood- 

 vessels with a sarcomatous adventitia springs from connective tissue 

 either in the general fibrous structures of the body or the interstitial 

 tissue of the viscera. Sections of these tumors sometimes reveal 

 thin-walled vessels with a distinct, broad zone of sarcomatous tissue 

 around them, resembling an enormously thickened adventitia of 

 embryonic tissue (Fig. 322). In other cases the embryonic tissue 

 that represents the adventitia of the separate vessels is fused into 

 a mass of sarcomatous tissue lying between the vessels. The tumor 



FIG. 339. 



Cavernous hsemangioma of the liver : a, substance of the liver; 6, fibrous capsule formed at 

 the margin of the angioma, probably the result of a chronic productive inflammation ; 

 c, space filled with blood ; d, atrophic wall between two of the spaces of the angioma. 



is then similar in structure to an ordinary sarcoma, in which the 

 vessels are more abundant, perhaps, than is usual. 



When the angiomata have been removed by operation the vessels 

 are usually emptied by the pressure that has been exerted upon their 

 tissues by the operative manipulations. This condition often gives 

 rise to puzzling appearances, when the endothelial cells of the vas- 

 cular walls are swollen or richer in cytoplasm than normal adult 

 endothelium. Sections of the tumor then look like sections through 

 a gland. The true nature of the tubules can generally be deter- 

 mined by the appearance of the lumina, which in the collapsed ves- 

 sels is not circular, while in the glands it is nearly so if the section 



