Secondary. Delay of blood favors. _Sarcoma_: horse, cattle, dog.
_Carcinoma_: horse, dog. _Melanoma_: common and large in gray and
white horses, rupture, external melanosis. _Angioma_: horse, ox.
_Lymphadenoma_: horse, ox, external adenoma.
The different tumors of the spleen are usually secondary. The intimate
structure of the organ, the peculiarity of the circulation through the
pulp cavities, and the delay of the blood in the pulp spaces, predispose
it in a very especial manner to the growth of neoplasms, the germs or
bioplasts of which are carried in the blood.
=Sarcoma.= In the _horse_ sarcomata have been found in the spleen
secondary to similar tumors in the other parts of the abdominal and
thoracic cavities. They may attain to any size, from a pea to the closed
fist and, in exceptional cases, of a mass which practically fills and
distends the abdominal cavity.
In the _cow_ an encephaloid sarcoma in the spleen, weighed nine pounds
and was associated with similar formations in the lymph glands generally
of the abdomen and chest.
In the _dog_ also sarcomata are common in the spleen.
=Carcinoma.= These are found in the _horse_ in connection with similar
primary tumors, as in the case of the sarcomata. They are at times
extremely vascular and soft, and at other times they are hard and
fibrous (scirrhus).
In the _dog_ secondary cancer of the spleen is comparatively common.
=Melanoma.= Black pigment tumors are especially common in gray and white
horses. Their common seat is on the black, hairless portions of the skin
(anus, vulva, perineum, tail, sheath, mamma, eyelids, lips, etc.), and
secondarily in the lymph glands and spleen. In the latter they may grow
to an extreme size, Wehenkel having mentioned one specimen of 60 pounds.
Its surface is marked by uneven, rounded black swellings, the entire
organ, indeed, seeming to be a conglomerate of these masses. The
intimate structure is that of a sarcoma, so abundantly charged with
black pigment granules that these appear to make up the greater part of
the mass.
Rupture of these neoplasms with the escape into the abdomen of blood
highly charged with the melanic matter is not uncommon.
The _symptoms_ of the splenic deposits are not usually recognizable, but
indications of chronic abdominal disease in connection with external
melanotic formations may well lead to a reasonable suspicion.
_Angioma._ In a _horse’s_ spleen weighing 30 lbs., there were numerous
soft nodules of a deep cherry color. These were cavernous masses with
connective tissue walls and the meshes filled with blood.
Similar vascular cavernous tumors have been found in the cow.
_Lymphadenoma_ has been found in the spleen of horses and cattle in
connection with the same disease of the lymph glands.
Like the other splenic tumors this is obscure and usually only found
after death. The existence of adenoid swellings elsewhere conjoined with
excess of white globules and indications of abdominal pain would be
suggestive of splenic disease.