Inflammation of the kidneys is either primary, secondary, or metastatic; in the first case it results from injury, concussion of the intestines, cold, or specific irritation (turpentine, cantharides, etc.); in the second it follows acute or chronic diseases, and it then presents a more or less remarkable type, corresponding to the general dyscrasia; in the third instance it arises chiefly from inflammations of the pelvis and calices, or from inflammations of the fascia adiposa and adjoining organs. The inflammation runs an acute or a chronic course; the idiopathic variety being particularly liable to the former.

The cortical substance is the chief seat of the first two varieties, as of textural alterations generally; when the inflammation commences at the pelves of the kidneys, the tubular substance is naturally implicated also. In the former case we often find one or both kidneys, either simultaneously or in rapid succession attacked throughout their substance; whereas the latter commences in spots from which it extends through the renal tissue.

The following are the anatomical characters of acute inflammation of the kidneys, modified of course by the degree and the acuteness of the affection.

Hyperaemic tumefaction and redness of the organ are followed by a uniform discoloration of the parenchyma which appears of a dirty brown or purple color, and filled with a dark sanguinolent fluid; it is either turgid and resistant, or collapsed, flabby, and very friable; or it may be turgid and friable, and the discoloration less uniformly grayish-red, or dirty white, accompanied by infiltration of a denser, coagulable, fibrinous substance, the texture is granular, the surface scattered over with an injected, asteroid, and polyhedral vascular network, and the fractured surfaces or sections made in the direction of the hilus, are streaked with striated vessels.

The general result of the infiltration is, that the organ is more or less swollen and discolored, and that its consistency is variously diminished. In accordance with what has been above remarked, we find the cortical substance chiefly affected; the affection is general or partial, and in the latter case it occupies particularly the superficial layer; in the first instance the swollen cortical substance is found to have forced its way into the basis of the pyramids, between the fasces of the tubuli, and they consequently appear unravelled and fimbriated.

The process not unfrequently extends to the tubular portion itself, or the latter is involved in the inflammation propagated from the pelvis. The pyramids then appear enlarged, swollen, pale; their color changed to a dirty brown, or grayish-red, and softened or indurated according to the nature of the inflammatory products; the inner membrane of the calices and pelvis is in both cases injected as in catarrhal inflammations, reddened and relaxed, and filled with an opaque, flaky, grayish, or yellowish-brown fluid.

Externally we find the fascia propria, and even the adipose covering of the kidneys involved in the inflammatory process: the former is easily detached from those portions of the surface which present the vascular injections above spoken of, its tissue is more or less injected and tumefied; the latter is infiltrated with serum, and softened.

This inflammation occasionally affects one kidney only, but very often both are simultaneously attacked: in the latter case, especially, it is liable to terminate fatally, in consequence of paralysis of the renal function with typhoid symptoms, resulting from retention of the urea in the blood; this is frequently complicated with serous effusion into the ventricles of the brain, or into the pulmonary tissue, followed by putrescence; or if the inflammation reaches a certain degree of intensity, suppuration, or an excessive retrograde process, or atrophy may result; or, lastly, the affection may become chronic.

Suppuration Is Not A Frequent Consequence

The inflammatory product which has been infiltrated in detached sections, or uniformly throughout the organ, is converted at first into small punctiform or millet-sized spots of white, creamy, or yellow pus, which subsequently coalesce into a small abscess. In its vicinity a renewed reactive process is set up, and we find a red injected halo, varying in size, which gives rise to a similar fusible product leading to an extension of the abscess. The original small abscesses are sometimes found scantily dispersed through the kidney, at others they are grouped together, at others, again, they are thickly sown through the entire kidney; they are then characterized by the surrounding inflammatory halo, and this renders them conspicuous though individually almost imperceptible.

They are always incomparably more numerous in the cortical substance; they here generally retain their rounded shape, even whilst enlarging, whereas in the tubular substance they are converted into elongated striated abscesses.

In the manner just described, as well as by the coalition of several abscesses, we see an extensive purulent accumulation brought about, which may increase so as to occupy one-half or two-thirds, or more, of the kidney. Moreover, there may be one or more of these accumulations, and their existence establishes phthisis renalis.

Renal abscess extends in the most various directions from the inflammation and suppurative fusion spreading through the kidney, and even beyond its sheath; we most frequently find it presenting excavations or sinuses, backwards and downwards; it causes death by exhaustion, or if the progress of the fusion is stopped, the surrounding parenchyma may become obliterated, or in the case when suppuration has extended beyond the latter, the fasciae of the kidney may become converted into cartilaginous tissue, and the abscess thus be enclosed and be borne for a long period; it may be reduced in size, and may even heal up, leaving a cicatrix; this is particularly liable to result after an opening and a discharge have been effected in a favorable direction.

This discharge may take place:

Firstly, into the cavity of the renal pelvis; the pus is then discharged by the urinary passages;

Secondly, into the peritoneal cavity;

Thirdly, externally in the lumbar region, by means of sinuses of various dimensions;

Fourthly, after previous agglutination of the intestine to the walls of the abscess and perforation, into the cavity of the former; it is evident that the ascending and descending colon, and the sigmoid flexure, are particularly liable to be thus involved, and in second order the duodenum.

Fifthly, renal abscess has also been seen to communicate with the lungs after perforation of the diaphragm; its contents are then expectorated in the shape of urinous-purulent sputa.

These discharges may sometimes take place in various directions at once; a combination of the discharge into the urinary passages with elimination of urine by a false passage - renal fistula, is of especial interest.

Termination in gangrene or gangrenous suppuration is extremely rare; it is more usual to find acute inflammation passing into the chronic form.

Chronic inflammation of the kidney either commences in that form, or is the result of acute inflammation, or, as is most frequently the case, it is the consequence of inflammation of the urinary passages, and especially of the calculous variety. It is distinguished from acute inflammation by a lower intensity of the symptoms, by its smaller extent, and by the variety of stages presented by the coexisting and consecutive inflammatory spots. Chronic inflammation also not unfrequently terminates in suppuration, which is particularly the case with the variety originating in calculous irritation of the renal pelvis; it also frequently terminates in induration and obliteration of the parenchyma, or induces atrophy of the kidney.

In the former case the coagulable portion of the infiltrated and accumulated product of inflammation is converted into a whitish, fibro-larda-ceous, cartilaginous callus, in which the renal parenchyma has entirely disappeared. The kidney is often found increased in bulk, and appears altered in shape, from the irregular accumulation of the product, giving rise to various tuberculated projections. This tissue may here, as elsewhere, subsequently become shrivelled and condensed, and is also, in a few cases, the seat of bone-earth deposit, osseous transformation, ossification.

Chronic inflammation is, like the acute form, frequently followed by atrophy of the kidney; inasmuch as not only its product but the original tissues themselves become absorbed. This secondary atrophy attacks either the entire kidney or sections of the organ, and the consequence is, accordingly, a uniform reduction of its size, or a partial contraction, which gives the kidney a shrivelled and uneven, lobulated surface. The contraction sometimes advances to such a degree, that the kidney appears reduced to the size of a hen's or even a pigeon's egg, it is surrounded by the tunica albuginea, that has become thickened by the inflammatory deposit, and by contraction, and forms a callous sheath of several lines in thickness; on closer examination we find the cortical substance reduced to a mere vestige; the pyramids are diminished to a size corresponding to the dimensions of the organ; the tissue generally is of a pale-red, or here and there of a slate-gray color, denser, tough, and fibro-cellular; occasionally, however, it is unusually dark-red, vascular, and congested, and all the vessels dilated. The calices and pelves are uniformly enlarged, the ureters contracted, their parietes shrivelled and thickened, and here and there approaching to obliteration, or actually obliterated.

Inflammation of the kidneys, with its consequences, has occasionally been discovered in new-born infants; but its frequency and importance are much more considerable at maturity and at the advanced periods of life.