In this condition there is a dilatation of the pelvis and calices of the kidney, as a result of obstruction of the ureter or urethra.

Obstruction of the urethra may be congenital or acquired. In the latter case there is first dilatation and hypertrophy of the bladder, which may afterwards be reflected to the ureters and pelvis. In all such cases the hydronephrosis will be double, although it is not always equal on the two sides.

Obstruction of the ureters may occur in any part of their course. Tumours or inflammatory swellings in the pelvic organs may obstruct the lower ends, and usually both ureters are affected. Calculi descend ing from the pelvis of the kidney occasionally cause obstruction. A peculiar form of obstruction is that in which the ureter does not, as in the normal condition, form a continuation of the pelvis of the kidney, but starts from it at an acute angle, passing obliquely through its walL This is probably a congenital malformation. Of similar origin is probably the occurrence of valves in the course of the ureter. More unusual causes are, pressure from without by a renal artery taking an unusual course so as to cross the ureter; abrupt bends in the ureter, which may be congenital, or may be from the ureter making an unusually abrupt turn over the brim of the pelvis when the edge has been rendered sharper than usual by emaciation.

It appears from the last instance that a comparatively small external pressure may obstruct the ureter, and that the urine in the pelvis and ureter is at such a low pressure as to be incapable of overcoming a comparatively slight resistance.

The existence of some of these causes has been doubted, chiefly the existence of a valved aperture by the ureter arising from the pelvis at an acute angle, and the occurrence of valves in the course of the canal. The author has two specimens of the former kind m the Western Infirmary Museum (see Catalogue), and Dr. Sainsbury has published an apparently undoubted case of the latter form. The author has also recorded a case in which a branch of the renal artery had so crossed the ureter just at its emergence from the pelvis as to produce an obstruction.

According to statistics collected by Newman, the obstruction arises, in the large majority of cases, either from obstruction of the urethra or from tumours of the pelvic organs, which may involve the ureters. These causes produced hydronephrosis in 400 out of 448 cases of double, and 133 out of 215 cases of single hydronephrosis. Renal calculi form the most frequent cause of single hydronephrosis.

The result of the obstruction is dilatation of the pelvis and calices (see Fig. 421 and Pig. 438, p. 972), but in addition there is frequently a considerable destruction of renal tissue. That is to say, the dilatation of the calices causes atrophy, first of the papillae which project into them, and then of the pyramidal portion of the kidney, advancing into the deeper parts of the organ. We thus somotimes find the pyramids as if cut abruptly across. But the condition frequently advances still further. The dilated calices increase in volume till, in the most extreme case, the kidney is replaced by a Cyst which represents dilated pelvis and calices, partitions existing in it corresponding to the divisions between the calices. When this has occurred, the cyst may go on enlarging so as to form a tumour of great bulk. The ureter is also dilated, often so greatly as to look like a piece of small intestine. It generally becomes convoluted in its course as well.

Hydronephrosis with granular atrophy of the kidney.

Fig. 421. - Hydronephrosis with granular atrophy of the kidney. The other kidney showed a marked com-punsatory hypertrophy. (VIRCHOW).

It is not in every case quite apparent what circumstances determine the degree of hydronephrosis. Complete obstruction leads usually to a comparatively slight hydronephrosis, the most extreme degree being reached in cases where on one side there is either an incomplete obstruction or one which gives way at intervals, such as a valved condition of the upper orifice of the ureter.

The ureter has been ligatured in animals and the processes observed. The first result is dilatation of the pelvis and of the ureter above the ligature. The tension of the urine in the ureter also rises up to a certain point, which, however, is far below the blood-pressure. When this point is reached the full extent of the distensile force derived from the secretion of the urine is attained. The secretion of the water of the urine, consisting in a transudation through the vessels of the glomeruli, is directly proportionate to the difference in pressure between the blood in the tufts and the fluid in the tubules, and when the pressure in the tubules is raised the secretion of urine ceases as soon as a state of equilibrium is brought about.

There are, however, two elements in the problem still to be considered. In cases where the ureter has been ligatured in animals the actual dilatation of the pelvis and calices has been comparatively slight, the state of equilibrium of tension being easily reached. And so in the human subject, when the obstruction is complete the pressure of the fluid in the dilated pelvis soon causes considerable obstruction of the renal vessels, and the power of secretion is reduced. But if, at times, an outlet is found for the urine and the pressure is suddenly reduced, there will be a relief of the vessels in the kidney and a violent hyperasmia leading to an excessive secretion of urine. As a matter of fact the sudden relief of an obstruction of the ureter has been found to be followed by an excessive secretion of urine which contained albumen. Where then there are such repeated sudden collapses and dilatations the advance of the hydronephrosis is most complete.

The fluid contained in the cavity is at first urine, but as the condition gets fully established the urinary constituents become absorbed and a watery albuminous fluid is found. In rare cases a colloid matter or a fatty milky fluid has been observed.

It sometimes happens that where a prolonged obstruction has existed the external fatty capsule of the kidney is greatly thickened, while only a moderate hydronephrosis exists, the external outline of the organ not being greatly increased. It is not unlikely that an cedema of the capsule following the obstruction of the ureter may be the cause of this great accumulation of fat by affording an extra supply of nourishing fluid, or perhaps by acting as a prolonged irritant.

We sometimes meet with cases' resembling hydronephrosis, but in which some of the cysts, representing dilated calices, do not communicate with the pelvis, but form Independent cysts. This occurs when from inflammation there has been partial or complete obliteration of the pelvis (see under Pyonephrosis).


Rokitansky, Lehrb., iii., Coats, Catal. of Western Inf. Museum, p. 119, 1885; Sainsbury, Path, trans., xxxvii., 1886; Newman, Lect. on Surg, dis. of kidney, 1888, and Glasg. Med. Jour., vol. xxxv., 1891.