414 DISEASES OF THE URINARY ORGANS. 



caseous nodules may be confined to the bases of the pyra- 

 mids. Discharge of the necrotic tissue often occurs into the 

 pelvis of- the kidney, which is generally also involved a 

 tubercular pyelo-nephritis. At a later stage the whole organ 

 is sometimes converted into a large sac, with caseous and ul- 

 cerating walls. 



TUMORS. 



Fibromata are not infrequently found in the kidney in the 

 form of small, firm, white nodules about the size of a millet- 

 seed, though sometimes much larger. 



Lipomata are rare, but the fatty external capsules of the 

 kidney may be so greatly increased in thickness as to form 

 practically a fatty tumor (Fig. 1 1 9). 



Simple adenoma has been met with in the kidney, but is 

 very rare. Small tumors sometimes occur, which are formed 

 of a displaced remnant of the suprarenal capsule, and histologi- 

 cally resemble that gland. 



Leiomyomata occasionally occur in the kidney, and are 

 generally situated near the apices of the papillae. A rare 

 tumor, which is usually congenital, is the rhabdomyosarcoma, 

 histologically found to be composed of round and spindle- 

 cells mixed with striated muscle-cells. 



Primary sarcoma of the kidney is more frequent than 

 primary carcinoma. Microscopically, it varies considerably 

 in size and appearance. Microscopically, the varieties most 

 frequently met are the round and spindle-celled, the myxo- 

 sarcoma, and myosarcoma. 



Primary carcinoma of the kidney is rare. It generally be- 

 gins in the cortex as an adeno-carcinoma. 



Cysts occur frequently in the course of chronic interstitial 

 nephritis, and even in the otherwise normal kidney, as the 

 result of obliteration and dilatation of the uriniferous tubules 

 and Bowman's capsule, and may attain sometimes a very con- 

 siderable size. They may be so numerous as to cause sur- 

 prise that the kidney should have been able to perform its 

 functions at all. Congenitally, both kidneys may be trans- 

 formed into masses of innumerable cysts of varying size, 

 these organs being so greatly enlarged in some cases as even 



