Renal stones grow upon the surfaces of the papillae, become detached and accompany the urine as it travels the collecting system. Since many of these stones are too large to negotiate the narrow conduits of the collecting system, they obstruct the flow of urine and often cause severe pain. Some stones are formed in the bladder, rather than in the kidney, but will not be considered here. There are five major categories of renal stones. I which represents reports on 1870 stones from four different series.
Calcium stones are clearly the most commonly occuring form of nephrolithiasis.
Calcium oxalate stones are more common than calcium phosphate, but mixed calcium oxalate - calcium phosphate are the most common variety. Struvite stones, usually seen in the setting of urinary tract infections, is the second most common type of renal stone. Uric acid stones, cystine stones and oxalate stones represent a relatively minor proportion of total stones formed, but are important in that they need to be recognized and it is potentially feasible to prevent their formation. Before discussing at farther length the important features of each subset of stones, theories pertaining to crystal formation, common to all types ofnephrolithiasis will be examined. The kidney on the one hand plays an important role in water conservation.