– The precipitation of normally occurring crystalline substances into irregularly shaped stones, which are deposited in the urinary tract, most commonly in the renal pelvis or calyces.
Causes and Incidence
Predisposing factors to calculus formation include obstruction and stasis of urine; urinary tract infection; dehydration and concentration of urine; prolonged immobility; vitamin A deficiency; dietary excess of vitamin D, calcium, protein, tea, or fruit juice; underlying disease of the small bowel; an underlying metabolic disorder (e.g., hypercalcemia or hyperparathyroidism); and hereditary disease (e.g., cystinuria). Renal calculi are common, and about 1 in 1,000 adults in the United States will be hospitalized with them. Four out of five individuals who develop calculi are men, and the peak onset is 20 to 30 years of age.
Certain conditions increase the supersaturation of urine with stone-forming salts, induce preformed salt nuclei, or reduce the production of crystal growth inhibitors. This allows the precipitation process to occur and stones to form, ranging in size from microscopic to several centimeters in diameter.
Many calculi are asymptomatic. If they obstruct the calyx, pelvis, or ureter, they cause severe pain that is typically described as traveling from the costovertebral angle to the flank and then to the suprapubic region and external genitalia. Back or abdominal pain, or both, may also be present. Chills, fever, nausea, vomiting, abdominal extension, and hematuria are also common.
Large stones can remain in the renal pelvis or calyx or hang up in the ureter and cause infection, necrosis, or obstruction, with subsequent hydronephrosis.
The diagnosis is based on clinical features plus an x-ray of the kidneys, ureter, and bladder, which demonstrates calculi, and a urinalysis, which may show hematuria, pyuria, and crystalline sludge in the sediment. Intravenous pyelography and computed tomography scans are also used to locate and visualize stones.
Pyelolithotomy or nephrolithotomy to remove large stones in kidney or ureterolithotomy to remove stones in the ureter that are not amenable to other treatment; nephrectomy when the kidney has been irreparably damaged.
Percutaneous stone dissolution with chemical solvents to shrink large uric stones in preparation for other retrieval methods; antiinfective drugs to treat infection; narcotic analgesics for pain; diuretics to prevent urinary stasis; cholestyramine for prophylaxis; for hypercalcinuria, allopurinol to reduce uric acid.
Small, solitary calculi without infection or obstruction may be treated by increasing fluid intake to encourage passage; extracorporeal shock wave lithotripsy (ESWL) is the treatment of choice for stones less than 2 cm in diameter; percutaneous nephrolithotomy is used in conjunction with ESWL to remove stones larger than 2 cm; cystoscopy with basket extraction can be used to remove calculi less than 1 cm in diameter that are lodged in the ureter; Prophylaxis: increased fluid intake; treatment of underlying conditions; reduction of excess calcium, phosphorus, purine, and oxalates in diet.