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Pediatric Stone Disease

Pediatric Stone Disease
Diagnosis of Stone Disease
Treatment for Kidney and Ureteral Stones
Surgery for Bladder Stones

Pediatric Stone Disease

Urinary stones (calculi) occur commonly in adults, but less often in children. Because of this, there is less known about the treatment of stones in children. Most pediatric urinary stones are treated in facilities and using instruments designed for stone removal in adults. This is only beginning to change, as pediatric urologists become more involved in the treatment of urinary stones.

Calculi in the urinary tract may be composed of a number of different materials. Stones form due to crystallization of solutes in the urine, which exist at a concentration high enough to exceed the saturation point. If you don't remember your high school chemistry, this means that stones form because there is too much of the ingredients of the stone, and not enough water in the urine. This can occur either because there is an abnormally high amount of stone-forming material in the urine, or the urine is too concentrated because of dehydration (thirst).

Materials that form stones include calcium (usually in the form of calcium oxalate, the most common type of stone in both children and adults), uric acid (the same chemical that causes gout), cysteine (only in children and adults with hereditary cystinuria) and magnesium ammonium phosphate (only in association with urinary infection). The incidence of calcium stones in adults is high, with the minority having a significant metabolic abnormality (an abnormal amount of chemicals in the blood or the urine). In children, stone formation is less common and, therefore, one is more likely to find that there is an underlying metabolic or anatomical abnormality in children who form stones.

Many of the children who form urinary stones have an underlying abnormality of the urinary tract. These include obstructions of the kidney or ureter, and diseases such as spina bifida and bladder exstrophy. These anatomical problems make the treatment of stones in children more complicated and require that any treatment be given in conjunction with a pediatric urologist.

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Diagnosis of Stone Disease

Stones are usually diagnosed in adults after an episode of pain or blood in the urine. These symptoms may occur in children, but often the stones are found on X-rays done for other reasons, or after vague and seemingly unrelated symptoms. Stones may be found anywhere in the urinary tract. Stones in the calyces of the kidney usually do not cause pain. Stones at the ureteropelvic junction or in the ureter can cause intermittent or continuous obstruction of the kidney, with resulting severe pain. Stones in the bladder may cause irritability with frequent urination and discomfort with urination. Stones often form in bladders that have been enlarged (augmented) with intestine and are usually asymptomatic.

When a stone in the ureter causes severe pain, it can often be relieved with narcotic medications given in the Emergency Room. Sometimes the pain will go away completely for days, or even weeks. This does not mean that the stone is gone and follow up X-rays should always be done to be certain. A stone that is left in the urinary tract for months or years, because of lack of symptoms, can cause severe damage to the function of the kidney or even result in loss of the kidney. A stone in the ureter will often "pass" spontaneously. Your doctor can tell by the size of the stone on the X-rays whether spontaneous passage is likely to occur. If not, the stone will need to be treated in other ways.

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Treatment for Kidney and Ureteral Stones

There have been remarkable breakthroughs in the past 20 years in the treatment of urinary stones. Prior to this time, the only option for removal of stones was an open operation. Now open surgery is very rarely performed for stone disease. If an open operation is proposed for your child's stone disease, ask about less invasive treatments that might be available.

The most futuristic treatment for urinary stones is extracorporeal shock wave lithotripsy (ESWL)-literally, breaking stones with shock waves from outside the body. In this form of treatment, X-rays or ultrasound are used to focus shock waves on the stone to break it without damaging the body's normal tissues. The safety of ESWL on the developing kidney has not been established beyond a doubt, but it seems from many large studies that this is a safe and effective way to treat pediatric kidney and ureteral stones. Although in adults, some forms of ESWL can be given without anesthesia, most children require at least sedation to keep them calm and to keep them from moving so that the focus on the stone can be maintained. The more powerful forms of ESWL are painful and children require anesthesia for this reason.

Most kidney stones in children can be treated with ESWL. There are several situations, however, in which other forms of treatment are necessary. If ESWL has failed to fragment a stone, another form of stone removal must be used. Also, some children are not candidates for ESWL because of their anatomy or previous reconstructive operations on their urinary tracts. Large stones may best be treated in a way that is likely to remove the entire stone, rather than subjecting the kidney to multiple ESWL treatments and the possibility of obstruction due to a "roadblock" of stone fragments in the ureter.

In these situations, endoscopic approaches are most useful. Endoscopy refers to using telescopes inside the body. The urinary tract has long been approached using "cystoscopes" (bladder scopes), as well as ureteroscopes and nephroscopes (kidney scopes). The specialty of "endourology" refers to the use of such telescopes to perform surgery within the urinary tract. The most common applications of endourology involve the removal of urinary stones.

Kidney stones may be approached endoscopically in two ways: through the bladder and ureter (ureteroscopically) or through the skin (percutaneously). The pediatric ureter is smaller than that of the adult and is subject to injury upon the passage of instruments, although the recent introduction of smaller flexible ureteroscopes has made this access feasible. More often than not, however, a percutaneous approach is used for a large stone burden.

The percutaneous removal of kidney stones (percutaneous nephrolithotomy, PCNL) was originally developed in Minnesota two decades ago. The techniques were developed for the removal of stones in adults and were used in children without modification, for the most part. A few groups have tried to "downsize" the instruments to make them more appropriate for children, but these efforts have been sporadic.

Recently, we have developed a technique referred to as the "mini-perc," which was specifically designed for pediatric PCNL, and also has been applied to adults. With the assistance of Cook Urological (Spencer, IN), we have developed a sheath for passage of miniature endoscopes (Circon/ACMI) allowing removal of kidney and ureteral stones through a small puncture.

The technique has been applied to many different stone types in children, ranging in size from 11 pounds up to adulthood. In most instances, our colleagues in interventional radiology will place a tube into the kidney the day prior to surgery. This is called a percutaneous nephrostomy tube and it gives us access to the kidney.

Sometimes we will skip this step and obtain access in the operating room. We pass a guide wire into the kidney, and over this wire pass a catheter (tube) that has two passages. This is then used to introduce a second "safety" wire. Then the catheter is removed and the sheath is inserted. In the older techniques, the kidney is dilated using plastic rods or a balloon and a 1-centimeter tube is placed in the kidney. The current technique allows us to place a small sheath (about 3.5 millimeters across) without dilating the substance of the kidney, hopefully resulting in lower blood loss and less kidney damage (this has not been proven scientifically at this time).

Once the sheath is in place, the stone(s) are either removed or fragmented and removed. Stones can be broken using several forms of energy, including laser, ultrasonic and electrohydraulic. Small rigid and flexible telescopes can be used to see all parts of the inside of the kidney and ureter. Stones and fragments can be removed using miniature graspers and baskets passed through the scopes. We have used the mini-perc technique for eight years with success equal to standard forms of percutaneous stone removal. It is important to know that more than one procedure is often necessary to remove all stone fragments, and that a small nephrostomy tube is left in the kidney until the process is completed.

References:
1. Jackman, S.V., Hedican, S.P., Peters, C.A., Docimo, S.G.: Infant and preschool age percutaneous nephrolithotomy: experience with a new technique. Urology, 52:697–701, 1998.
2. Docimo, S.G.: Endoscopic surgery in children. In Marshall, F.F., Textbook of Operative Urology, W. B. Saunders, Baltimore, pp. 198–206, 1996.

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Surgery for Bladder Stones

Bladder stones in the United States are most commonly associated with urinary tract reconstruction, either for bladder exstrophy or neurogenic bladder. Stones often form in bladders that have been enlarged or "augmented." Percutaneous techniques are now used routinely to remove such stones, often on an outpatient basis. We have shown that the use of percutaneous techniques to remove bladder stones results in an average hospital stay of one day, as opposed to approximately five days for open surgery. None of the patients studied who had percutaneous surgery required pain medication at the time of discharge, as opposed to all of the patients who had open surgery. When available, we feel that percutaneous bladder stone surgery is superior to open surgery.

Reference:
1. Docimo, S.G., Orth, C.R., Schulam, P.G.: Percutaneous cystolithotomy after augmentation cystoplasty: comparison with open procedures. Techniques in Urology, 4:43–45, 1998.

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Last Update
April 1, 2010
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Last Update
April 1, 2010
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