Nephrolithiasis

Alternative names:

kidney stones; renal calculi; stones - kidney

Definition:

A condition in which one or more stones are present in the pelvis or calyces of the kidney or in the ureter (see also cystinuria).

Causes, incidence, and risk factors:

A kidney stone results when the urine becomes too concentrated and substances in the urine crystallize to form stones. Stones may not produce symptoms until they begin to move down the ureter, causing pain. The pain is severe, located in the flank, and often described as "the worst pain ever experienced."

Kidney stones are common. About 5% of women and 10% of men will have at least one episode by age 70. Kidney stones affect about 2 out of every 1,000 people. Recurrence is common, and the risk of recurrence is greater if two or more episodes of kidney stones occur. Kidney stones are common in premature infants.

Some types of stones tend to run in families. Some types may be associated with other conditions such as bowel disease, ileal bypass for obesity, or renal tubule defects. A personal or family history of stones is associated with increased risk of stone formation. Other risk factors include renal tubular acidosis and resultant nephrocalcinosis.

Calcium stones are most common, accounting for 75 to 95% of all stones. They are two to three times more common in men, usually appearing at age 20 to 30. Recurrence is likely. The calcium may combine with other substances such as oxalate (the most common substance), phosphate, or carbonate to form the stone. Oxalate is present in certain foods. Diseases of the small intestine increase the tendency to form calcium oxalate stones.

Uric acid stones are also more common in men. They are associated with gout or chemotherapy. Uric acid stones make up about 8% of all stones.

Cystine stones may form in persons with cystinuria. It is a hereditary disorder affecting both men and women.

Struvite stones are mainly found in women as a result of urinary tract infection. They can grow very large and obstruct the kidney, ureter, or bladder.

Other substances may crystallize, precipitate, and form stones.