When a calculus remains in the pelvis of the kidney without completely obstructing the flow of urine, it usually increases in size, while the resulting irritation may be the cause of fresh deposits either upon the surface of the original calculus or in the form of new concretions. In this way immense deposits of urinary salts may be formed. Thus, in a case given in detail in the second series of Boston City Hospital Reports there was found upon the one side a calculus which when perfectly clean and dry weighed 204 grammes, filling the whole dilated pelvis and sending prolongations into the calices, so that its shape was compared to that of a hippopotamus. The resemblance was made more complete by the wrinkling and roughness of the exterior. In the other kidney were several hundred calculi, from the size (and shape) of a large almond down to that of white mustard-seed. The latter were composed of two apparently distinct substances—one a reddish-brown, looking like uric acid, and the other of the color and polish of white marble; both, however, were phosphates.
The amount of local disturbance produced in the pelvis of the kidney by the presence of a foreign body seems to depend somewhat upon the character of its surface. Rough and uneven calculi, such as oxalate of lime, are apt to produce inflammation much more rapidly than smooth and polished ones, but it is seldom that any calculus remains without some pyelitis. At first only a loss of polish of the mucous membrane, with a little increase of mucus, may be observed, to which succeed roughening and suppuration with occasional fibrinous deposit. The pelvis, more or less dilated, may then contain a quantity of mucopurulent urine, with perhaps some blood, in which are concealed the stones which have given rise to this condition, and often phosphatic deposits not converted into calculi.
Pyelitis is divided by some foreign writers into catarrhal and diphtheritic—a distinction rather of degree than of kind. The mucous membrane of the pelvis may, like other mucous membranes rarely, and like serous membranes often, throw out a fibrinous exudation which takes the form of false membrane. This indicates intensity of inflammation, but has no necessary connection with diphtheria. A true diphtheritic pyelitis, that is, connected with the general disease known as diphtheria, is of course a conceivable lesion, but certainly not a common one.
The renal symptoms—especially true albuminuria, so common and of such grave import in this disease—are due to lesions of the secreting substance, and not of the pelvis. It is important, but not always easy, to decide whether there is more albumen present than is to be accounted for by the pus. The pyelitis may be acute or chronic, being characterized by the intensity of the attack and the rapidity with which the symptoms subside. The prospect of a given attack being acute is decided largely by the supposed cause: a small calculus passing into the ureter undoubtedly gives rise in most instances to a localized pyelitis, which subsides after the cause of irritation has disappeared. An inflammation from a larger one remaining is naturally of slower development, but may be more acute while the calculus remains rough and irritating, and partially subside when it becomes covered with a smoother coating of phosphates. The mucous membrane, however, is not likely to regain a completely healthy condition.
The mucous membrane in severe pyelitis may be deeply eroded, and even perforated, so that the contents of the pelvis escape and give rise to abscess in the perinephritic or prevertebral cellular tissue, which may be discharged through the loins with resulting cure, or the establishment of a fistula, from which issues pus and at times calculi. Among the rarer results of perforation may be mentioned gastro-nephric and duodeno-nephric fistulæ. These might be diagnosticated by the presence of food and other intestinal contents in the urine, provided that the ureter were still pervious. Vomiting of calculi and urine has been reported by the older writers.
The writer is indebted to J. R. Chadwick for references to two modern cases—one where such a fistula was diagnosticated during life;16 and another where a gastro-nephric fistula was found after death.17 In the latter case a diagnosis would have been impossible, as the kidney was disorganized and the ureter occluded. The extent to which the renal secreting substance suffers in calculous pyelitis varies considerably, and is very probably connected with the amount of pressure exercised either by the calculus itself when it attains a large size or by the urine in cases of obstruction. It is rare for either pyelitis or hydro-nephrosis to exist entirely independently.
16 Giornale di Anat. e Fis. path., iii. p. 370.
17 Marquezy, Thèse de Paris, 1856.
The changes which take place are those of atrophy. Interstitial suppurative nephritis seems to follow this form of pyelitis much less frequently than that which is due to extension upward of disease in the lower urinary passages.
Corresponding to the pressure of solid or fluid, the papillæ are eroded and the straight tubes shortened. In the cortical substance, which soon becomes diminished in thickness, the interstitial tissue is hypertrophied, dense, and hard, while the tubes become smaller or in time disappear. The Malpighian bodies are changed to dense masses of connective tissue, but are still plainly recognizable, irregularly crowded together instead of being arranged as usual in more or less symmetrical double rows. The cortex of the kidney may thus become but little more than a mere skin stretched over a large stone, with perhaps here and there a piece of renal structure recognizable and in a comparatively normal condition.