Kidney stones (calculi) are hardened mineral deposits that form in the kidney. They originate as microscopic particles and develop into stones over time. The medical term for this condition is nephrolithiasis, or renal stone disease.

Small stones can cause some discomfort as they pass out of the body. Regardless of size, stones may pass out of the kidney, become lodged in the tube that carries urine from the kidney to the bladder (ureter), and cause severe pain that begins in the lower back and radiates to the side or groin. A lodged stone can block the flow of urine, causing pressure to build in the affected ureter and kidney. Increased pressure results in stretching and spasm, which cause severe pain.

Stone Formation
Kidney stones form when there is a high level of calcium (hypercalciuria), oxalate (hyperoxaluria), or uric acid (hyperuricosuria) in the urine; a lack of citrate in the urine; or insufficient water in the kidneys to dissolve waste products. The kidneys must maintain an adequate amount of water in the body to remove waste products. If dehydration occurs, high levels of substances that do not dissolve completely (e.g., calcium, oxalate, uric acid) may form crystals that slowly build up into kidney stones.

Treatment depends on the size and type of stone, the underlying cause, the presence of urinary infection, and whether the condition recurs. Stones 4 mm and smaller (less than 1/4 inch in diameter) pass without intervention in 90% of cases; those 5-7 mm do so in 50% of cases; and those larger than 7 mm rarely pass without intervention. Patients are advised to avoid becoming sedentary, because physical activity, especially walking, can help move a stone.

If possible, the kidney stone is allowed to pass naturally and is collected for analysis. The patient is instructed to strain their urine to obtain the stone(s) for analysis. It is important to analyze the chemical composition of kidney stones to determine how to prevent recurrent stone formation. The urine may be strained using an aquarium net or another device. Each voiding should be strained until the physician instructs the patient otherwise.

Dietary changes may be required and fluid intake should be increased. Patients with stones must increase their urinary output. Generally, 2000 cc of urine per day (slightly more than 1/2 gallon) is recommended and patients should drink enough water to produce this amount of urine daily. In some cases (e.g., some cystine stone formers), even higher levels of fluid intake are required.

Dietary calcium usually should not be severely restricted. Reducing calcium intake often causes problems with other minerals (e.g., oxalate) and may result in a higher risk for calcium stone disease.

If a kidney stone does not move through the ureter within 30 days, surgery is considered. Urologists use several procedures to break up, remove, or bypass kidney stones.

This procedure can be used to remove or break up (fragment) stones located in the lower third of the ureter. A fiberoptic instrument resembling a long, thin telescope (ureteroscope) is inserted through the urethra and passed through the bladder to the stone. Once the stone is located, the urologist either removes it with a small basket inserted through the ureteroscope (called basket extraction) or breaks the stone with a laser or similar device. The fragments are then passed by the patient. Ureteroscopy is performed under general or local anesthesia on an outpatient basis.

This procedure is effective for stones in the kidney or upper ureter. It uses an instrument, machine, or probe to break the stone into tiny particles that can pass naturally. Lithotripsy is not appropriate for patients with very large stones or other medical conditions.

Ultrasonic lithotripsy
uses high frequency sound waves delivered through an electronic probe inserted into the ureter to break up the kidney stone. The fragments are passed by the patient or removed surgically.

Electrohydraulic lithotripsy (EHL)
uses a flexible probe to break up small stones with shock waves generated by electricity. The probe is positioned close to the stone through a flexible ureteroscope. Fragments can be passed by the patient or extracted. EHL requires general anesthesia and can be used to break stones anywhere in the urinary system.

Extracorporeal shock wave lithotripsy (ESWL)
uses highly focused impulses projected from outside the body to pulverize kidney stones anywhere in the urinary system. The stone usually is reduced to sand-like granules that can be passed in the patient's urine. Large stones may require several ESWL treatments. The procedure should not be used for struvite stones, stones over 1 inch in diameter, or in pregnant women.

Patients undergoing lithotripsy are given a sedative and general or local anesthesia, and the procedure takes over an hour. More than one treatment may be required.

Percutaneous Nephrostolithotomy (PCN)
This surgical procedure is performed under local anesthesia and intravenous sedation. Percutaneous (i.e., through the skin) removal of kidney stones (lithotomy) is accomplished through the most direct route to stones through the kidney. A needle and guidewire are used to access the stones. The surgeon then threads various catheters over the guidewire and into the kidney and manipulates surgical instruments through the catheters to fragment and remove kidney stones. This procedure achieves a better stone-free outcome in the treatment of medium and large stones than shock wave lithrotripsy. This procedure usually requires hospitalization, and most patients resume normal activity within 2 weeks.

Ureteroscopic Stone Removal
This procedure is performed under general anesthesia to treat stones located in the middle and lower ureter. A small, fiberoptic instrument (ureteroscope) is passed through the urethra and bladder and into the ureter. Small stones are removed and large stones are fragmented using a laser or similar device. A small tube (or stent) may be left in the ureter for a few days after treatment to promote healing and prevent blockage from swelling or spasm.

Open Surgery
This procedure requires general anesthesia. An incision is made in the patient's back and the stone is extracted through an incision in the ureter or kidney. Most patients require prolonged hospitalization and recovery takes several weeks. This procedure is now rarely used for kidney stones.

Prevention of renal stone disease depends on the type of stone produced, underlying urinary chemical risk factors, and the patient's willingness to undergo a long-term prevention plan. The patient may be asked to make lifestyle modifications such as increased fluid intake and changes in diet.

Orange juice and lemonade with real lemon juice are good sources of citrate and may be recommended as an alternative to water. Limiting meat, salt, and foods high in oxalate (e.g., green leafy vegetables, chocolate, nuts) in the diet may also be recommended. Medication may be prescribed and treatment for an underlying condition that causes renal stone disease may be necessary.

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