322 



TUMORS. 



hand some of them so closely resemble some forms of carcinoma as to be 

 with difficulty distinguished from them. The endotheliomata originate 

 in that form of connective-tissue cells called endothelium, lining blood 

 and lymph vessels or lymph spaces, and develop by a proliferation of 



FIG. 165. ENDOTHELIOMA OF ANTRUM. 

 This complex form of endothelioma, resembling types of adenoma, not infrequently occurs in the ovary. 



these cells (Figs. 163 and 164). Sometimes the cells of the endotheliomata 

 resemble closely the normal endothelium ; sometimes, however, they differ 

 considerably from them, being occasionally very large, often thick and 

 irregular in shape, and even nearly cylindrical or cuboidal like certain 

 forms of epithelium (Fig. 165). They are associated with a more or less 



abundant vascular stroma, 

 which may be alveolar in 

 formation. In this case, as 

 in alveolar sarcoma, it may 

 often be seen that the cells 

 have an intimate relationship 

 to the trabeculae of the stroma. 

 Developing from the eu- 

 dothelium of the vessels or 

 lymph spaces, these tumors 

 sometimes exhibit a structure 

 closely simulating that of 

 tubular glands lined with 

 more or less cuboidal epithe- 

 lium or papillary augio-sar- 



comata (Fig. 166). It is in many cases difficult to decide from the 

 structure in the fully developed parts of a tumor whether it is an en- 

 dothelioma, an adenoma, or a carcinoma. In such cases a careful study of 



FIG. 106. ENDOTHELIOMA OF HUMERUS. 

 Tj^pc resembling angio-sarcoma. 



