Renal Calculi The Most Common Cause of Urinary Tract Obstruction

The most common cause of urinary tract obstruction is urinary calculi. The term nephrolithiasis refers to kidney stones. Although stones can form in any part of the urinary tract, most develop in the kidneys. About 1 million North Americans are hospitalized each year with kidney stones, and an equal number are treated for stones with out hospitalization. Kidney stones are crystalline structures made up of materials that the kidneys normally excrete in the urine. 

They require a nidus, or nucleus, to form and a urinary environment that supports continued precipitation of stone components to grow. It is thought that the urine normally contains substances that inhibit precipitation of stone components. 

Three major theories are used to explain stone formation: the saturation theory the inhibitor deficiency theory and the matrix theory.’3 One or more of these the ories may apply to stone formation in the same person. The saturation theory states that the risk of stone formation is increased when the urine is supersaturated with stone components (e.g., calcium salts, urc acid, magnesium ammonium phosphate ( cystine). The inhibitor the ory suggests that persons who have a deficiency of endogenous compounds that inhibit stone formation in their urine are at increased risk for stone formation. One such compound has been identified and called nephrocalcm. The matrix theory proposes that organic materials, such as mucopoiysaccharides derived from the epithelial cells that line the tubules, act as a nidus for stone formation. This theory is based on the observation that organic matrix materials can be found in all layers of kidney stones. it is not known whether the matrix material contributes to the initiation of stone formation or the material is merely entrapped as the stone forms.