Causes and pathogenesis of polycystic kidney disease

The first attempt to explain the causes of polycystic kidney disease was the creation of the inflammatory-retention theory, put forward in 1865 by R. Virchow. Other theories were also proposed (syphilitic, neoplasm theory), which are currently of only historical interest.

Most authors believe that polycystic kidney disease has teratogenic causes, which arise as a result of disruption of embryonic development of the kidneys at the stage of fusion of the excretory and secretory apparatuses, when in a number of nephrons there is no contact of the growing ureter rudiment with the metanephrogenic tissue. Renal tubules that are not connected to the excretory system undergo cystic degeneration. Progressing, this process leads to increased compression of the parenchyma and the death of a significant portion of the nephrons.

According to new research, the cause of polycystic kidney disease is a disorder of ampulla division. The ampulla induces the formation of a nephron. After division, one half of the ampulla joins the nephron, the other induces a new nephron, with which it then joins. Both ampullae divide again and form a new nephron.

The size of the cysts depends on the secretory pressure and tissue resistance of the underdeveloped excretory tortuous tubules. This can explain the presence of cysts of various sizes - from pinpoint, small to large. In this regard, the question is relevant: do all the nephrons in the cystically degenerated areas die or do some of them continue to function? Checking the function of the nephrons of polycystic kidneys, some researchers have proven by introducing inulin and creatinine that the altered nephrons, especially with small cysts, function, since provisional urine formed by filtration through the glomerulotubular system of the kidney was found in the contents of the cysts. From this follows a conclusion that is important in practical terms: during the operation of ignipuncture, cysts should not be destroyed whose diameter does not exceed 1.0-1.5 cm.

Cysts are located over the entire surface of the kidney between normal renal tissue. This is confirmed by the data of histological examination, when along with the changed glomeruli and nephrons, normal glomeruli and tubules are found in the preparations. R. Scarpell et al. in 1975 put forward a hypothesis according to which the development of cysts in the kidneys is associated with immunological incompatibility of metanephrogenic blastoma and ureteral germ. They confirm their assumption by the fact that the concentration of C3 complement of the complement system decreases in the blood serum of patients with polycystic kidney disease.

Polycystic kidney disease is always a bilateral developmental anomaly, and the number and size of cysts are often different in both kidneys. Often, simultaneously with polycystic kidney disease, patients also have polycystic liver and pancreas disease, 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 renal structure anomalies is pyelonephritis, which is latent for a long time and only after some time manifests itself clinically. This is largely due to the violation of the passage of urine and the features of abnormal lymph and blood circulation in the kidneys. The development and progression of renal failure depends not only on the degree and severity of pyelonephritis, but also on the number of switched off neurons. The occurrence and development of pyelonephritis is also facilitated by venous stasis caused by compression of the renal vein and its branches by large cysts. Venous stasis in the kidney leads to anoxia and increased permeability of the vascular wall, which in turn entails edema of the renal stroma, creating the most favorable conditions for the development of infection in the interstitial tissue of this organ.

The occurrence and development of bilateral chronic pyelonephritis in polycystic kidneys leads to drastic functional changes not only in the kidneys but also in the liver. Protein, prothrombin-forming, antitoxic, carbohydrate, fat, deaminating, enzymatic and steroid metabolism is disrupted. Improvement of liver functional activity indices during conservative preoperative treatment is a favorable prognostic sign.

There was an opinion that the development of polycystic kidney disease proceeds in the same way in both newborns and adults. However, N.A. Lopatkin and A.V. Lyulko (1987) provided data showing that polycystic kidney disease in children and adults differs both in pathogenetic and clinical terms.

Classification of polycystic kidney disease

Many authors, taking into account the morphological features and clinical course of polycystic kidney disease, distinguish polycystic disease in newborns, children, adolescents, and adults. In-depth clinical, genetic, and morphological analysis has shown that despite significant differences between polycystic kidney disease in newborns, children, and adolescents, this pathological condition is essentially the same. Polycystic disease in children is characterized by an autosomal recessive type of inheritance of the disease, but the mutation occurs in different genes.

In newborns, polycystic kidneys are uniformly enlarged, their embryonic lobulation is preserved. In the section of the kidney, the cysts are of the same size and shape, locally scattered among the normal parenchyma, the cortex and medulla are not clearly delineated. In older children and adolescents, the morphological picture of polycystic kidney disease differs in that more than 25% of the tubules are already involved in the pathological process. The kidneys are significantly enlarged, the surface is tuberous. Cysts are visible through the fibrous capsule. In the section, among the dull renal parenchyma, many cysts are scattered, no longer of the same size, as in newborns, but of different sizes, although they are smaller than in adults. The lumen of the tubules is dilated, compressed in places, the nephrons are underdeveloped.

In adults, the amount of unchanged parenchyma is significantly reduced. The fluid in the cysts is transparent, purulent during inflammation, and brown during hemorrhages. The contents of the cysts differ from plasma in the composition of the main electrolytes and consist of urea, uric acid, and cholesterol. When the kidneys are cut, their surface is dotted with cysts of varying diameters. As a rule, large cysts alternate with small ones, scattered throughout the renal parenchyma, resembling irregularly shaped honeycombs.

Depending on the duration of the process and the degree of secondary complications, the parenchyma acquires a grayish tint, and its functional capacity progressively decreases.

Microscopic examination of uncomplicated cysts shows that their internal surface is lined with cubic epithelium. The walls of the cysts consist of a thin layer of dense connective tissue, penetrated by small non-pulpable nerve bundles, spreading in underdeveloped smooth muscles. The number of nerve structures is significantly reduced when an infection is added. The death of nerve elements in a polycystic kidney is due to anoxia due to ischemia of the renal tissue.

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