Result of hyperplasia of connective tissues and compression and
absorption of parenchyma. Unilateral or partial. Causes: chronic
productive inflammation, calculus in tubes, ureter, or pelvis, tumor,
retention cyst, embolism. Lesions: sclerosis of kidney, firmness,
pallor, anæmia, lack of glomeruli and tubules, cysts, congenital,
urinous retention, colloid. Symptoms: reduced secretion, palpation of
kidney. Treatment: Prevention: arrest conditions, abundance of water,
succulent food, parasiticides, operation on cysts, counteract
nephritis.
Unlike hypertrophy, this is constantly the result of a pathological
process. So long as a normal functional activity of the secreting
elements is carried on, such parts must maintain their size and healthy
characters. But with the compression of such secreting elements
(glomeruli and convoluted tubes) by a hyperplasia of connective tissue,
by pressure from without or from the damming back of the urine in the
pelvis and tubes, the secretory elements are absorbed and removed, and
the final result is a general atrophy. If such atrophy appears in both
kidneys at once it can only be very partial in extent, as extreme
atrophy of both, with loss of their secretory function, would entail
poisoning and death from the retained urinary products. The comparative
frequency of the disease may be inferred from the reports of the numbers
of specimens found by Barrier and Moussu in old horses in the dissecting
rooms. The latter observed a dozen cases in a single winter, other
examples are recorded by Cadeac (horse), Soula (swine) and Trasbot (in
various animals).
_Causes._ The most common source of the condition is the occurrence of
chronic productive inflammation. The new product in such cases, if not
pus, or a growth that rapidly passes into fatty or granular
degeneration, or into gangrene, tends to form tissue of a low
organization, especially fibrous. The resulting increase of the fibrous
trabeculæ, in undergoing subsequent contraction necessarily compresses
the secretory tissue and the final result is a visible and, it may be,
extreme wasting. Hence any slowly advancing productive inflammation is
liable to result in absorption and removal of the kidney parenchyma, and
distinct atrophy of the gland.
Again the obstruction of the ureter by a calculus in the pelvis which
falls into the infundibuliform entrance, or a stone arrested at any part
of the duct (or even of the urethra) or by worms, hydatids, cysts or
tumors, throws back on the kidney the secreted urine, which distending
the pelvis and uriniferous tubes leads to direct compression and
absorption of the secretory parenchyma. Direct compression of the kidney
by an adjacent tumor will act in a similar manner. Retention cysts by
their gradual increase and augmenting pressure cause absorption of the
gland tissue.
The blocking of individual uriniferous tubules by minute calculi, which
is so often seen in cattle, kept on dry feeding in winter, is a cause of
partial nephritis, and absorption, as noted by Röll.
A somewhat rare cause of atrophy is the diminution of the blood supply
by arteritis and embolism of the renal artery, or by pressure of tumors
on that vessel. Arteritis and blocking suggests at once the possible
agency of the strongylus (sclerostoma) armatus in the horse. Trasbot
records a striking instance of compression of the renal artery and
kidney by an enormous sublumbar melanoma. This occurred in an aged horse
and led to atrophy.
_Lesions._ In cases due to productive inflammation with sclerosis of the
kidney, the firmness, pallor and bloodlessness of the organ is a marked
feature. When incised it is found to be composed mainly of fibrous
tissue, while the glomeruli and tubuli have to a large extent
disappeared.
If there has been simple lack of circulation the kidney becomes flaccid,
pale and small in size. The secretory elements (glomeruli and
uriniferous tubes) are first absorbed, leaving the fibrous network,
which tends to shrink and form a hard resistent mass. In extreme cases
there may be absolutely no glandular tissue left, and the dense shrunken
mass represents only the hyperplasia of the original fibrous network. In
the different successive stages of this process the glomeruli and
tubules become flattened, the epithelial cells become granular, or
contain colloid casts and refrangent elements like oil globules and
finally they are represented by a small mass of fibrous material.
Of all the atrophies caused by the pressure of tumors perhaps that
caused by cysts is the most characteristic. There may be a single cyst
or they may be multiple; they may range in size from a pea to the size
of the two fists the total size exceeding that of the normal kidney. In
all such cases the cysts project visibly from the surface of the organ.
They vary according to their origin and nature. Congenital cysts are
said to have resulted from distension by retained urine of the capsule
of the glomerulus. The arterial tuft is atrophied and flattened against
the wall. Serous cysts with clear contents are found in the old. Urinous
cysts again form by distension of the tubules that are obstructed by
cysts or minute calculi. Colloid cysts are found in certain forms of
nephritis formed by the dilatation of the capsule of the glomerulus or
of the uriniferous tubules. The liquid often contains leucin, tyrosin
and cholesterine. In all such cases the walls of the cyst become thick,
and the glandular parenchyma is compressed leading to progressive
degeneration and atrophy.
_Symptoms_ of atrophy of the kidney are necessarily those of suppression
of urine, with, in certain cases, the passage of casts of the
uriniferous tubes and of crystals of salts. There are, however, no
absolutely pathognomonic symptoms. When the kidney can be reached
through the flaccid walls of a comparatively empty abdomen, or through
the rectum, its hard, shrunken condition may assist in diagnosis.
_Treatment_ is not successful in advanced cases. _Prevention_ is to be
sought by obviating or treating the conditions on which the atrophy
depends. Nephritis must be treated on general principles. Calculi must
be avoided by a liberal supply of water, by soiling, or by pasturage.
Strongylus parasitism should be dealt with by destroying the parent
worms in the bowels, and by securing pure drinking water free from their
eggs and embryos. Cysts, and tumors are only amenable to surgical
measures and not often open even to these.