_Sarcoma._ This is usually a secondary formation from the primary tumors
in the spleen and peritoneum, and it occurs as multiple masses
throughout the substance of the gland. The liver is greatly increased in
size, extending far beyond the last rib on the right side, and weighing
when removed as high as 70 ℔s. (Mason), or even 88 ℔s. (Cadeac), in
extreme cases.
The whole surface of the liver may show bulging, rounded masses, and the
morbid growth may have involved the capsule and caused adhesion to the
back of the diaphragm (Bächstädt). The cut surface of the neoplasm is
smooth, elastic, yellowish and circular or oval in outline. It may have
a variable consistency—friable or tough, according to the activity of
growth and the relative abundance of cells and stroma. The portal glands
are hypertrophied and thrombosis of the portal vein is not uncommon.
Microscopic examination of the dark red scrapings shows numerous blood
globules, intermixed with the round or spindle shaped cells and nuclei
of the tumor. Sections of the tumor show these cells surrounded by a
comparatively sparse fibrillated stroma. The round cells may vary
from .005 to .05 m.m. They contain one or more rather large nuclei and a
number of refrangent nucleoli. The nuclei are often set free by the
bursting of the cells in the scrapings. They become much more clearly
defined when treated with a weak solution of acetic acid. Small grayish
areas in the mass of the tumor represent the original structure of the
liver, the cells of which have become swollen and fatty.
A liquid effusion more or less deeply tinged with red is usually found
in the abdominal cavity.
_Symptoms_ are those of a wasting disease, with some icterus, sometimes
digestive disorder, and a marked enlargement of the liver. The last
feature can be easily diagnosed by palpation and percussion. If an
examination through the rectum detects the enlargement and irregular
rounded swellings of the surface of the liver or spleen, or the
existence of rounded tumors in the mesentery or sublumbar region, this
will be corroborative. The precise nature of the neoplasms can only be
ascertained after death.
_Melanoma._ Melanosis of the liver is comparatively frequent, especially
in gray horses, and above all when they are aging and passing from dark
gray to white. In many cases a more certain diagnosis can be made than
in sarcoma for the reason that primary melanotic neoplasms are
especially likely to occur on or near the naturally dark portions of the
skin, as beneath the tail, around the anus or vulva, in the perineum,
sheath, eyelids, axilla, etc. The extent of the disease is likely to be
striking, the liver, next to the spleen, being the greatest internal
centre for melanosis. The whole organ may be infiltrated so that in the
end its outer surface is completely hidden by melanotic deposit. The
surface deposits tend to project in more or less rounded, smooth masses
of varying size according to the age of the deposit and the rapidity of
its growth. Individual deposits may vary in size from a pea to a mass of
40 or 50 lbs. They are moderately firm, and resistant, and maintain a
globular or ovoid outline. The color of the melanotic deposits is a deep
black with a violet or bluish tint. If the pigmentary deposit is in its
early stage it may be of a dark gray. The deposits are firmer than the
intervening liver tissue and rarely soften or suppurate.
Melanosis in the horse is not always the malignant disease that it shows
itself to be in man, and extensive deposits may take place externally
and considerable formations in the liver and other internal organs
without serious impairment of the general health. It is only in very
advanced conditions of melanosis of the liver that appreciable hepatic
disorder is observed. If, however, there is marked enlargement of the
liver, in a white or gray horse, which shows melanotic tumors on the
surface, hepatic melanosis may be inferred.
_Lymphadenoma. Adenoid Tumor._ Lienaux describes cases of this kind in
which the liver was mottled by white points which presented the
microscopical character of adenoid tissue, cells enclosing a follicle
and a rich investing network of capillaries.
_Angioma._ These are rare in the horse’s liver, but have been described
by Blanc and Trasbot as multiple, spongy tumors on the anterior of the
middle lobe, and to a less extent in the right and left, of a blackish
brown color, soft and fluctuating. The largest mass was the size of an
apple, and on section they were found to be composed of vascular or
erectile tissue. The tendency is to rupture and extensive extravasation
of blood (30 to 40 lbs.) into the peritoneum.
_Carcinoma. Epithelioma._ These forms of malignant disease are not
uncommon in the liver as secondary deposits, the primary lesions being
found in the spleen, stomach, intestine, or pancreas, or more distant
still, in the lungs. The grafting or colonization of the cancer in the
liver depends on the transmission of its elements through the vena portæ
in the one case, and through the pulmonary veins, the left heart and
hepatic artery in the other.
_Lesions._ The liver may be greatly enlarged, weighing twenty-seven
pounds (Benjamin) to forty-three pounds (Chauveau), hard, firm, and
studded with firm nodules of varying sizes. These stand out from the
surface, giving an irregular nodular appearance, and are scattered
through its substance where, on section, they appear as gray or white
fibrous, resistant, spheroidal masses shading off to a reddish tinge in
their outer layers. Microscopically these consist of a more or less
abundant fibrous stroma, enclosing, communicating alveoli filled with
cells of various shapes and sizes, with large nuclei (often multiple)
which stain deeply in pigments. The relative amount of fibrous stroma
and cells determines the consistency of the mass, and whether it
approximates to the hard cancer or the soft. In the horse’s liver they
are usually hard, and, on scraping off the cut surface, yield only a
limited quantity of cancer juice. In the epithelial form, which embraces
nearly all that have originated from primary malignant growth in the
walls of the intestine, the epithelioid cells, flattened, cubical,
polyhedral, etc., are arranged in spheroidal masses or cylindrical
extensions, which infiltrate the tissues more or less. These seem in
some cases to commence in the radical bile ducts (Martin), and in others
in the minor coats of the larger biliary ducts.
As the disease advances a brownish liquid effusion is found in the
abdomen, and nodular masses formed on the surface of the peritoneum.
_Symptoms._ As in other tumors of the liver these are obscure. As the
disease advances there may be œdema of the legs and sheath, indications
of ascites, stiff movements, icterus, occasional colics, tympanies, and
diarrhœa. Nervous symptoms may also appear, such as dullness, stupor,
coma, vertigo and spasms. Emaciation goes on rapidly and death soon
supervenes.