Although renal calculi (kidney stones) may form anywhere in the urinary tract, they usually develop in the renal pelvis or the calyces of the kidneys. Such formation follows precipitation of substances normally dissolved in the urine (calcium oxalate, calcium phosphate, magnesium ammonium phosphate or, occasionally, urate or cystine).
Renal calculi vary in size and may be solitary or multiple. They may remain in the renal pelvis or enter the ureter and may damage renal parenchyma; large calculi cause pressure necrosis. In certain locations, calculi cause obstruction, with resultant hydronephrosis, and tend to recur.
Among Americans, renal calculi develop in 1 in 1,000 people, are more common in men (especially those ages 30 to 50) than in women, and are rare in blacks and children. They're particularly prevalent in certain geographic areas, such as the southeastern United States ("stone belt"), possibly because a hot climate promotes dehydration or because of regional dietary habits.
Although the exact cause of renal calculi is unknown, predisposing factors include the following:
Signs and symptoms
Typical symptoms include sharp mid-back pain, blood in the urine, painful urination, nausea, and vomiting.
Other associated signs include fever, chills, hematuria (when calculi abrade a ureter), abdominal distention, pyuria and, rarely, anuria (from bilateral obstruction or unilateral obstruction in the patient with one kidney).
The clinical picture in conjunction with the following diagnostic tests allows a diagnosis:
Diagnosis must rule out appendicitis, cholecystitis, peptic ulcer, and pancreatitis as potential sources of pain.
Because 90% of renal calculi are smaller than 5 mm in diameter, treatment usually consists of measures to promote their natural passage. Along with vigorous hydration, such treatment includes antimicrobial therapy (varying with thecultured organism) for infection; analgesics, such as meperidine, for pain; and diuretics to prevent urinary stasis and further calculus formation. (Thiazides decrease calcium excretion into the urine.)
Prophylaxis to prevent calculus formation includes a low-calcium diet for absorptive hypercalciuria, parathyroidectomy for hyperparathyroidism, and allopurinol and urinary alkalynization for uric acid calculi.
Calculi too large for natural passage may require surgical removal. When a calculus is in the ureter, a cystoscope may be inserted through the urethra and the calculus manipulated with catheters or retrieval instruments. A small-diameter telescope, the ureteroscope, may be inserted through the ureter to remove stones from the ureter and kidney. Extraction of calculi from other areas (kidney calyx, renal pelvis) rarely may necessitate a flank or lower abdominal approach.
Percutaneous ultrasonic lithotripsy and extracorporeal shock-wave lithotripsy shatter the calculus into fragments for removal by suction or natural passage. To prevent recurrence of calculi, the patient will also need teaching before discharge.
If there is a history of stones, fluids should be encouraged to produce adequate amounts of dilute urine (usually 6 to 8 glasses of water per day). Depending on the type of stone, medications or other measures may be recommended to prevent recurrence.
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