ATROPHY OF THE KIDNEY.
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.