KIDNEY, DISEASES OF. (For the anatomy of the kid neys, see URINARY SYSTEM.) The results of morbid processes in the kidney may be grouped under three heads : the lesions pro duced, the effects of these on the composition of the urine, and the effects of the kidney-lesion on the body at large. Affections of the kidney are congenital or acquired. When acquired they may be the result of a pathological process limited to the kidney, or an accompaniment of disease in other parts of the body.
Congenital principal congenital affections are anomalies in the number or position of the kidneys or of their ducts; atrophy; cystic disease and growths. The most common abnormality is the fusion of originally separate kidneys and production of a single kidney, or if the fusion is more complete, a disc-like mass with two ureters. The kidneys may be situated in abnormal positions; thus they may be mistaken for tumours. In some cases atrophy is associated with mal-develop ment, so that only the medullary portion of the kidney is devel oped ; in others it is associated with arterial obstruction, or ob struction of the ureter. In congenital cystic disease the organ is transformed in whole or part into a mass of cysts, and the enlarge ment of the kidneys may be so great as to produce difficulties in birth. The cysts found in granular kidney are of the retention variety and are produced by constriction of urinary tubules by the fibrous tissue. In some cases cystic degeneration is accompanied by anomalies in the ureters and in the arterial supply. Growths of the kidney are sometimes found in infants ; they are usually malignant, and may consist of a peculiar form of sarcoma, termed rhabdo-sarcoma, owing to the presence in the mass of voluntary muscular fibres. These tumours depend on anomalies of develop ment ; the tissue which forms the primitive kidney belongs to the same layer as that which forms the muscular system (meso blast). Anomalies of the excretory ducts are various. The ureter may be double or much dilated and the pelvis of the kidney may be greatly dilated, with or without dilatation of the ureter.
Acquired Affections.--One or both of the kidneys in the adult (especially women) may be preternaturally mobile, con stituting a movable kidney, either because it has a partial mesen tery (floating kidney) or, more commonly, because it is loose under the peritoneum and not efficiently supported in its fatty bed. Movable kidney produces a variety of indefinite symptoms, such as pain in the loin and back, faintness, nausea and vomiting.
In some cases the movable kidney may be kept in its place by a pad and belt, but in others it requires surgical fixation with sutures The operation is neither difficult nor dangerous, and its results are excellent.
arrangement of the renal blood-vessels is peculiarly favourable to the production of cone-shaped areas of necrosis, the result of blockage by clots. Usually the clot is detached from the interior of the heart, and if the plug is infective owing to the presence of septic micro-organisms, a pyaemic abscess results. It is exceptional for the large branches of the renal artery to be blocked, so that the symptoms in ordinary cases are only the temporary appearance of blood or albumen in the urine. Blocking of the main renal vessels as a result of disease of the walls of the vessels may lead to disorganization of the kidneys. Blocking of the veins, leading to extreme congestion of the kidney, occurs in cases of extreme weakness and wasting and sometimes in septic conditions, as in puerperal pyaemia, where a clot formed in one of the pelvic veins spreads up the vena cava and secondarily blocks the renal veins Passive congestion of the kidneys occurs in heart diseases and lung diseases, where the return of venous blood is interfered with. It may also be produced by tumours pressing on the vena cava. The engorged kidneys become brownish-red, enlarged and fibroid, and they secrete a scanty, high-coloured urine.