TUMORS. 331 



they are encapsulated, they form metastases through the blood. 

 They usually result fatally in the human, even after operation, 

 probably because of the liljeration of considerable of the adrena- 

 lin substance which increases blood pressure to such an e.xtent 

 that heart failure supervenes. 



PLACENTOMA. 

 (Syncytioma.) 



A placentoma is a tumor composed of tissue similar to the 

 chorionic villi. 



These tumors have been described under a variety of names 

 as syncytioma malignum, deciduoma malignum, chorio-epithel- 

 ioma, epithelioma seritonale, chorio-carcinoma. ( )nl}- ;-eccmiy 

 have placentomata been recognized as distinct tumors. 



A placentoma is essentially a tumor of the uterus. They are 

 not common in domestic animals but this may be because of rail- 

 ure to recognize them. The uterus or fallopian tube is their 

 most frequent location. They occur more frecpiently after spur- 

 ious or mole-pregnancy and usually appear a short time after 

 parturition. Abortion is a predisposing cause. The primary 

 tumor almost in\-ariably occurs in the uterus thuugh a few cases 

 have been reported in women in which the primary tumor \\as 

 in the kidney. They are very malignant. 



These tumors appear as soft, spongy, villous, bleeding masses 

 and are variable in size. The^■ have the general appearance of 

 placenta or foetal membranes in both the primary and the metas- 

 tatic tumors. They begin to develop at the cotyledons or zone 

 of placental attachment and rapidly extend into the uterine mus- 

 cular tissue and in\'ade blood vessels, thus metastases nccur 

 in a short time after the tumor appears. Because of their struct- 

 ure (embryonic cells and rich vascular supply) they gro\y raj)- 

 idly. 



The presence of a placentoma is indicated by uterine hem- 

 orrhage occurring a few days after normal parturition or abor- 

 tion. The uterus is enlarged and the affected individual rapidly 

 becomes anemic and emaciated. The uterine discharge usually 

 contains shreds of the tumor and the cavity of the uterus is 

 occupied with a soft bleeding mass. 



Microscopically, these tumors are composed of a protoplasmic 

 ground-substance, which is arranged in an irregular network 

 forming alveoli. The protoplasmic mass is usually continuous, 

 there being no evidence of cell partitions, and it contains many 

 nuclei thus forming a syncytium. Within the alveoli of the pro- 



