Stone, or calculi, commonly form in kidney tissue or the draining structures of the urinary tract as a result of disease, infections, or incompletely defined problems of mineral excretion. The most common types of stones contain various combinations of calcium, magnesium, phosphorus, or oxalate. Less common types are due to inherited disorders characterized by excretion of abnormal amounts of cystine or xanthine. Recurrence of most stones can be prevented by therapy based on analysis of the stones, the urine, and the blood.
Kidney stones range in size from less than 5 mm (0.20 in) to over 25 mm (1.0 in) in diameter. They tend to run in families and four out of every five patients with kidney stones are male, usually between the ages of 20 and 30. Differences in dietary and fluid intake may put certain people at higher risk for kidney stones.
When a stone causes erosion of tissue, blood appears in the urine; when one lodges in the ureters, there may be severe pain in the side extending to the lower abdomen and groin. Other complications include obstruction to urine flow, persistent infection of the kidneys, and progressive tissue damage with loss of kidney function.
Most solitary stones are passed in the urine, but others require medical treatment. Percutaneous removal employs a fiberoptic nephroscope, through which forceps, a basket, or a loop is inserted to extract the stone through the skin. A noninvasive technique uses narrowly focused acoustic shock waves to break up the stones. To break up stones in the lower ureter, the narrow canal between the kidney and the bladder, a laser guided by optical fibers may be used.