TUMORS OF DOMESTIC ANIMALS 25 
LYMPHOSARCOMA 
Lymphosarcoma or malignant lymphoma is a variety of round-cell 
sarcoma which produces more cell reaction than a simple hyperplasia 
of a lymphatic structure. The principal characteristic of lympho- 
sarcoma is that it infiltrates and perforates rather than metastasizes. 
These neoplasms are often found in the mediastinum and may in- 
volve any structure of the thoracic cavity. They grow rapidly, fol- 
lowing the connective tissue of the mediastinum, and envelop the 
trachea and bronchi, following the interlobular connective tissue to 
the root of the lung. They may also extend along the aorta and 
larger vessels, invade the pericardium, and infiltrate the heart mus- 
cle. The infiltration may also extend along the esophagus, or along 
the course of the vagi or the phrenic nerves, as well as the sheaths of 
muscles of the diaphragm. 
Lymphosarcoma in domestic animals occurs also in the abdominal 
cavity, producing marked thickening of the intestinal walls and the 
stomach. It is also frequent in the kidney, spleen, liver, and repro- 
ductive organs. 
Microscopically lymphosarcoma consists of small, round cells iden- 
tical in appearance with lymphocytes. The cells are fairly uniform 
in size and have a large nucleus slightly displaced to one side, leav- 
ing very little cytoplasm around the periphery and staining well 
with nuclear dyes. 
Although the infiltrating property of lymphosarcoma follows the 
course of lymph vessels which is not the course of ordinary sarcoma, 
the infiltration from one lymph follicle to another follows, forming 
finally a fused mass, but does not become generalized as in leukemia. 
Such extensive local invasion by continuity of structure is referred to 
by some writers as lymphosarcomatosis. Metastasis by the blood 
vessels is very uncommon, and secondary deposits in other organs are 
rarely found. 
ALVEOLAR SARCOMA 
Alveolar sarcoma is not a separate variety of sarcoma so far as the 
appearance of the cells is concerned. Alveolar sarcomas are usually 
a subvariety of round-cell sarcoma, but may be also of the spindle-cell 
t} 7 pe, with the ceils varying in size. It is probably more common in 
domestic animals than in man and is considered very malignant. 
The chief characteristic t>f alveolar sarcoma is the arrangement of 
cells in groups or nests simulating somewhat the fobules of a gland. 
These groups or islands of cells are separated from one another by 
bands or septse of interstitial connective tissue. In rare instances the 
alveolar effect may be produced by an arrangement of spindle-shaped 
sarcomatous cells, but in the type most frequently encountered the 
alveoli are rendered more prominent by the connective-tissue trabecu- 
le separating the groups of cells, and this form is much coarser than 
the lymphadenoid reticulum found in the lymphosarcoma. The con- 
nective-tissue trabecular support the blood A T essels, which may be 
very abundant. Alveolar sarcoma is highly malignant and grows 
where any sarcomas are found, but shows marked preference for the 
skin and serous membranes, notably the pleura and peritoneum. Al- 
veolar large round-cell sarcoma may be mistaken for carcinoma if the 
character of the cells is not taken into consideration. 
