Where do the renal stones form and how?

Stone formation is the result of a series of events including crystal nucleation, growth and aggregation, crystal retention within the kidneys and evolution of retained crystals into stone nidus. Site of stone formation is determined by the location of crystal nucleation, transit time through the renal tubules, and the rate of crystal growth and aggregation. Structure and function of kidneys play significant role in these processes. Urinary supersaturation with respect to various stone salts and the crystallization inhibitory potential of urine depend on functional state of the kidneys. Under normal conditions urinary conditions are suitable for nucleation of calcium phosphate in the loop of Henle and for calcium oxalate crystals in the collecting ducts but crystals stay small and are excreted in the urine. However, in conditions where supersaturation is high and conditions are favorable for size enhancing processes of crystal growth and aggregation, crystals deposit in renal tubules at sites of disturbed urine flow. Crystals present in the superficial tubules of renal papilla ulcerate to the papillary surface and develop into the kidney stones.