Hydronephrosis

Hydronephrosis means dilation of the pelvis of the kidney by urine which has accumulated, because of obstruction of the urinary tract at some point distal to the pelvis, most commonly the pelvi-ureteral junction. If the obstruction be at a lower level, the ureter becomes dilated first, and the kidney is involved later. Occasionally the obstruction is confined to one or more of the minor calyces. Formerly it was considered that either intermittent or gradually increasing obstruction was required to produce this condition, and that sudden complete obstruction led to anuria and atrophy, but Hinman and others have shown by animal experiment that complete obstruction is followed much more frequently by hydronephrosis than by primary atrophy. The increased intrapelvic pressure is in turn transmitted to the renal tubules, which dilate and press upon the adjacent veins, thus impeding the circulation and accelerating the process of atrophy of the parenchyma. Indeed, experiments have shown that ischaemia is more important in the causation of atrophy than back-pressure on the tubules. At first the tubules in the peripheral portion are compressed, and here also pressure on veins exercises a damaging influence on blood-supply. The glomeruli appear not to become dilated, but to undergo fibrous atrophy. Nevertheless the kidney continues to function for long periods even when there is only a thin shell of renal tissue left-otherwise, of course, the sac would cease to increase in size. This has an important bearing on treatment, and constitutes a strong argument for conservative surgery rather than nephrectomy of these damaged organs. In early cases function can improve enormously if the obstructive factor be removed, and in late cases the process can at least be arrested, and the individual left with some active renal tissue. Under normal circumstances the pressure in pelvis and ureters is nil, and in experimental animals it is found that a rise of 10 mms. of mercury leads to a diminished output of urine which ceases altogether when the pressure rises to 20-30 mms. Probably for this reason the hydronephrosis produced by complete obstruction becomes stationary in size when this pressure is reached. Normally, however, in the human, hydronephrosis is not (except as an accidental event) produced by complete but by partial obstruction, so urine continues to be filtered through but much less concentrated and of lower specific gravity than on the normal side. Duncan Morison has shewn that in hydronephrotic sacs, colloids, solutions, …