Fibromas are frequently met with in the kidneys in the form of small white tumours of no practical significance, but they have also been found of large size. Lipomas are very rare in the kidney, but the fatty external capsule sometimes forms a bulky tumour (Lipoma cap-sulare).

Cysts

Cysts of various kinds are of peculiarly frequent occurrence in the kidneys, and they are of various kinds. In some cases they arise distinctly from obstruction of the tubules, as in the contracted kidney of interstitial nephritis already mentioned.

Simple cysts are frequently met with in kidneys which are otherwise perfectly normal, and the cysts themselves do not, as a rule, seriously interfere with the functions of the organ. They are larger or smaller well-formed cysts, which not infrequently project from the surface of the organ. They contain usually a clear fluid, but the contents are sometimes colloid in character. The wall of the cyst is composed of connective tissue lined with a proper tesselated epithelium. These cysts sometimes grow to a large size, and may push aside the renal tissue to a large extent. It is probable that they are of congenital origin, arising by an isolated occurrence of the same process as that which produces the following form.

Cystic transformation of the kidneys is also a condition of congenital origin, at least in many cases, and probably in all. The whole kidney is converted into a congeries of cysts of larger and smaller size. The cysts form rounded prominences from the surface, and on section (Fig. 439) they are seen to replace the renal tissue. The wall of each cyst is composed of a tunica propria with well-formed tesselated epithelium lining it. It contains usually a clear fluid, but the fluid may be brownish or even hemorrhagic, and it is noteworthy that it contains the constituents of the urine, often with albumen, and sometimes throws down a granular precipitate of uric acid. Between the cysts there is very little space, but there are traces of remaining renal tissue, and the pelvis and ureter are present. The outline of the organ is greatly enlarged.

Kidneys of this kind have been frequently* met with in new-born children, in whom they may reach the dimensions of eight inches by four. From their size they may seriously interfere with parturition, even requiring evisceration before delivery can be effected. It is of importance to note that this condition often co-exists with other congenital defects such as hydrocephalus, defective urinary bladder, and horse-shoe kidney, and that it frequently coincides with a cystic condition of the liver.

Fig. 439. - Cystic transformation of kidney, shown in section. The other kidney was similar.

Cystic degeneration is also met with in the adult, and it is remarkable that the functions of the organs may be preserved for a long time, although both kidneys are composed of a congeries of cysts, as in the figure. The author met with a case in which the patient died at the age of forty^three. For eighteen years before his death there had been recurring attacks of hematuria, and he at last died with uremic symptoms. The kidneys were much enlarged and cystic, but with some renal tissue remaining between the cysts.

The cysts undoubtedly arise by dilatation of the uriniferous tubules and glomeruli, the medullary tubules being, according to Kennedy, chiefly concerned. The dilatation is generally ascribed to constriction, so that the cysts are regarded as Retention cysts. There are serious objections to this view, pure and simple. The cysts are obviously growing structures of well-formed tissue, and scarcely like the small dilatations in chronic nephritis. Again, the general aspects of the condition, both clinically and pathologically, are not those of a chronic nephritis such as would produce obstruction. There is rather, it may be for many years, a slowly advancing transformation of the tubules, without any of the ordinary signs of Bright's disease, so that the actual diagnosis is usually made post mortem. From his own observation, the author believes that the condition arises probably from a perverted function of the renal epithelium. In a case of the kind he found that the beginnings of the cysts seemed to be the formation of small clumps of colloid matter in the tubules, formed as if by abnormal secretion. The character of the secretion prevented its passage down the tubule, and it may be supposed that the continuation of this abnormal secretion would produce gradual enlargement. An origin such as this would be consistent with the fact that cystic disease of the liver frequently coincides with that of the kidneys, and that in some cases there are atao cysts in the pancreas, lungs, etc.

Dermoid cysts are also met with in the kidneys.

Adenoma

This form of tumour is very rare. It is described as occurring in the kidneys in the form of defined solitary growths of various sizes up to that of a walnut. It occurs in the cortical substance, and arises from the convoluted tubules. According to structure two forms are described, a papillary and an alveolar, these resembling the corresponding forms in the ovaries.

It is not uncommon to meet with small tumours consisting of pieces of Displaced suprarenal capsule. The tumours lie immediately under the capsule of the kidney, but may be deep in the renal substance; they are distinctly defined from the kidney tissue. Under the microscope they show cylindrical masses of cells which are infiltrated with fat.

Primary Sarcoma

This occurs in various forms. It is stated that cases described as cancer are frequently sarcomas (Dickinson). The early age at which cancers of the kidney are stated to occur lends support to this view, as, in general, children are much more liable to sarcomas than cancers.

The forms chiefly met with are round-celled and spindle celled sarcoma, myxosarcoma, and myosarcoma. The tumours generally grow rapidly and may assume large dimensions. They occur mostly in early life.

The Myosarcoma is a specially interesting form. It is composed of round or spindle-celled tissue, with which is mixed striped muscle in the form either of elongated cells or cylinders. The tumour is probably congenital in its origin, being only met with in very young children (under eighteen months). It grows rapidly and is usually bilateral. The view of Cohnheim is probably correct, that the tumours arise by foetal inclusion. The first rudiment of the uro-genital organs is close to the proto-vertebrae, and it seems probable that some of the germinal muscle cells from the latter have been included with the cells forming the rudiments of the kidney, and have afterwards formed the tumours. Metastasis has been observed, and in one case the secondary tumours contained muscle.

Primary Cancer

This tumour is usually unilateral, although there have been cases of bilateral cancer. The tumour is in most cases virtually a cancerous degeneration of the organ. The kidney may be completely converted into a tumour, which sometimes attains a very large size, retaining the general shape of the organ and covered by its capsule. The pelvis is also usually recognizable, although the cancerous tissue may have grown into it. But in some cases Only a part of the kidney is involved, and in that case, while the affected part retains the general shape of the organ, although enlarged, the remaining piece of kidney has quite its normal appearance. To the naked eye it is as if a portion of kidney were transformed, and with the microscope it can be seen, at the margin of normal and pathological, that the tumour is advancing by a conversion of the proper kidney tissue. The epithelium of the tubules is multiplying so as to form the cancerous epithelium, and is becoming irregular in form (Fig. 440), while the cancerous stroma is being formed of the connective tissue of the organ. A rare form of cancer of the kidney is that illustrated in Fig. 441. Here an isolated tumour has formed instead of the usual transformation of the kidney tissue.

Fig. 440. - A uriniferous tubule at the border of an advancing cancer. The epithelium is undergoing transformation, x 300.

In regard to the form of cancer, there are some cases in which the structure has been that of the cylinder-celled epithelioma, in others more that of ordinary cancer. A partial colloid transformation has been observed in a few cases. Whatever the form the tissue seems to originate from the kidney structures.

The tumour is usually very soft, but it is generally confined within the capsule of the kidney. If it passes beyond the capsule it does so more readily into the retroperitoneal tissue than to the peritoneum, and it may thus extend along the wall of the trunk into the pleura.

The growing tumour not infrequently extends into the pelvis of the kidney and the renal veins. Hence arise hematuria on the one hand, and thrombosis of the veins on the other. The thrombosis may be very extensive, the clot propagating itself in various directions.

In a case observed by the author there was a very extensive thromboais, involving the veins of both legs. In another case cancerous elements were present in the thrombus, and some of these had been conveyed to the lungs; they were detected along with the clot inside the pulmonary artery, embolism having occurred.

Fig. 441. - Unusual form of cancer of kidney. There is a rounded tumour at the upper end. (Froro a painting by Dr. A. Macphail).

Secondary Tumours

Metastatic tumours are not frequent in the kidneys. Cancers and Sarcomas occur. Melanotic sarcoma also occurs.

Malignant lymphoma and Leuksemic tumours are perhaps the com-, monest. As seen with the naked eye, they form rounded tumours affecting the cortex chiefly, and causing great enlargement. Under the microscope they present round-celled tissue infiltrated between the tubules.

Literature

Tumours - Kelynack, Renal growths, 1898. Cysts - Bayer, Traits des malad. des reins, iii.; Virchow, Ges. Abhandl., 871; Eve, Path, trans., xxxi., 164, 1880; Pye-Smith, ibid., xxxii., 1881, and xxxvi., 1885; Thorn, Beitr. zur Genese d. Cystenniere, 1882; Kennedy, (with literature) Laboratory Bep., Edinburgh, iii., 1891; Bitchie, (summaries of cases) ibid., iv., 1892; Ewald, Verhandl. d. Berlin Med. Gesellsch., xxii. and xxiii.; von Kalhden, Ziegler's Beitr., xiii., 1893. Adenoma - Sturm, Archiv d. Heilk., 1875; Weichselbaum u. Greenish, Oest. Med. Jahrb., 1883; Grawitz, Virch. Arch., xciii., 1883; Marchand, ibid., xcii., 1883. Sarcoma - Dickinson, 1. c.; Newman, 1. c. Myosarcoma - Cohnheim, Virch. Arch., Iv., 1872, and lxv., 1875; Eve, Path, trans., xxxiii., 1882; Williams, ibid.; Bibbert, Virch. Arch., cvi., 1886. Cancel - Waldeyer, Virch. Arch., lxi. and lxiv., 1875; Pereverseff, ibid., lix., 1874; Ebstein, D. Arch. f. klin. Med., xxx.; GAIRDNERand Coats, Glasg. Med. Jour., iii., 1871; Brodeur, Affections du Bein, 1886, p. 170; Newman, 1. c.