The causes and pathogenesis of polycystic kidney disease
Last reviewed: 23.04.2024
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The first attempt to explain the causes of polycystic kidney was the creation of an inflammatory-retention theory, put forward in 1865 by R. Virchow. Other theories (syphilitic, neoplasm theory) have been suggested, which at the present time are of only historical interest.
Most authors believe that the cause of polycystic kidney disease is teratogenic, which arise as a result of embryonic development of the kidneys at the stage of fusion of the excretory and secretory apparatus, when in a number of nephrons there is no contact of the growing ureteral bud with metanephrogenic tissue. The renal tubules, not connected to the outflow system, undergo cystic degeneration. Progressing, this process leads to an increase in compression of the parenchyma and the death of a significant part of nephrons.
According to new research, the cause of polycystic kidney disease is a violation of ampoule division. Ampoule induces nephron formation. After division, one half of the ampoule joins the nephron, the other - induces a new nephron, with which it then connects. Both ampoules are divided again and form a new nephron.
The size of the cysts depends on the amount of secretory pressure and tissue resistance of the underdeveloped excretory sinuous tubules. This can explain the presence of cysts of different sizes - from point, small to large. In this regard, the question is urgent: do all nephrons in the cystic-degenerate areas die or some of them continue to function? Checking the function of the nephrons of polycystic kidneys, some researchers have shown that altered nephrons, especially in small cysts, function because the contents of the cysts show a provisional urine produced by filtration through the glomerulo-canalic kidney system. This leads to a conclusion that is important in practical terms: during the operation of a needle pad it is not necessary to destroy cysts, whose diameter does not exceed 1.0-1.5 cm.
Cysts are located on the entire surface of the kidney between normal renal tissue. This is confirmed by histological examination data, when along with the changed and glomeruli and nephrons, normal glomeruli and tubules are found in the preparations. R. Scarpell et al. In 1975, put forward a hypothesis that the development of cysts in the kidneys is associated with the immunological incompatibility of metanephrogenic blastoma and ureter sprout. They confirm their supposition by the fact that in the serum of patients with polycystic kidney the concentration of the complement C3-complement of the complement system decreases.
Polycystic kidney is always a bilateral anomaly of development, with the number and size of cysts very often being different in both kidneys. Often simultaneously with polycystic kidney disease, polycystosis of the liver and pancreas is also revealed in the patients, which is explained by close functional and morphological correlations of these organs.
The main factor determining the occurrence and progression of renal failure in patients with an anomaly of the kidney structure is pyelonephritis, which for a long time is latent and only after a while manifests itself clinically. This is largely contributed to the violation of the passage of urine and the peculiarities of abnormal lympho- and blood circulation in the kidneys. The development and progression of renal failure depend not only on the degree and severity of pyelonephritis, but also on the number of excluded neurons. The venous stasis, caused by compression of the renal vein and its branches with large cysts, also contributes to the emergence and development of pyelonephritis. Venous stasis in the kidney leads to anoxia and an increase in the permeability of the vascular wall, which in turn entails edema of the kidney stroma, creating the most favorable conditions for the development of infection in the interstitial tissue of this organ.
The emergence and development of bilateral chronic pyelonephritis in polycystic kidneys leads to abrupt functional changes not only in the kidneys, but also in the liver. Violated protein, prothrombin, antitoxic, carbohydrate, fat, deaminating, enzymatic and steroid metabolism. Improvement of liver function in the process of conservative preoperative treatment is a favorable prognostic sign.
There was an opinion that the development of polycystic kidneys proceeds in the same way as in newborns and adults. However, N.A. Lopatkin and A.V. Lulko (1987) reported that polycystic kidney disease in children and adults varies both pathogenically and clinically.
Classification of polycystic kidney disease
Many authors, taking into account the morphological features and clinical course of polycystic kidney, distinguish polycystosis of newborns, children, adolescents, adults. An in-depth clinical genetic and morphological analysis showed that despite significant differences between polycystic kidneys in newborns, children and adolescents, this pathological condition is essentially the same. For polycystic childhood, the autosomal recessive type of inheritance of the disease is characteristic, but the mutation occurs in different genes.
In newborns, polycystic kidneys are evenly enlarged, their embryonic lobulation persists. On a cut of a kidney cysts have the same size and the form, are locally scattered among normal parenchyma, the cortical and cerebral layers are not clearly delimited. In older children and adolescents, the morphological picture of polycystic is distinguished by the fact that more than 25% of the tubules are involved in the pathological process. The kidneys are considerably enlarged, the surface is tuberous. Cysts shine through the fibrous capsule. On a cut among dull renal parenchyma the set of cysts is already not the same size as in newborns, but different, although they are less than in adults. The lumen of the tubules is widened, sometimes compressed, the nephrons are underdeveloped.
In adults, the amount of unchanged parenchyma is significantly reduced. The fluid in the cysts is clear, with inflammation - purulent, with a hemorrhage is painted in a brown color. The contents of the cysts differ from the plasma in the composition of the basic electrolytes and consists of urea, uric acid, cholesterol. On a cut of kidneys their surface is strewn with cysts of various diameters. As a rule, large cysts alternate with small cysts scattered throughout the parenchyma of the kidney, resembling bee honeycombs of irregular shape.
Depending on the prescription of the process and the degree of secondary complications, the parenchyma acquires a grayish shade, and its functional capacity progressively decreases.
Microscopic examination of uncomplicated cysts shows that their inner surface is lined with cubic epithelium. The walls of the cysts consist of a thin layer of dense connective tissue, permeated with small, non-messy nervous beams that propagate in the underdeveloped smooth muscles. The number of nerve structures is significantly reduced when an infection is attached. The death of nerve elements in the polycystic kidney is due to anoxia on the soil of ischemia of the kidney tissue.
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