Patient information: Kidney stones in children

INTRODUCTION — Kidney stones (also called nephrolithiasis or urolithiasis) develop when a collection of minerals or other material form a small "stone" in the kidney, ureter, or bladder. The stone can cause pain, block the flow of urine, and cause long-term kidney problems if it is not recognized and treated promptly. Fortunately, most children who develop kidney stones recover without any long-term complications.

Stones are less common in children than in adults, although the number of children who develop stones is unclear. Most children who develop kidney stones have an underlying condition that increases their risk of stones, although some children develop a stone for unknown reasons.

This topic review discusses how and why kidney stones develop, and the symptoms, diagnosis, treatment, and ways to prevent a recurrence of kidney stones. A topic review that discusses kidney stones in adults is available separately. (See "Patient information: Kidney stones in adults").

HOW KIDNEY STONES DEVELOP — A brief overview of the anatomy of the urinary tract will help to explain how kidney stones develop. The urinary tract is composed of two kidneys and ureters, a bladder, and a urethra (show figure 1). Urine is produced by the kidneys, which are located towards the middle of the back, below the ribs.

The kidneys remove waste products and excess fluid from the blood and convert this to urine. The urine passes out of the kidney through small tubules into the hollow portion of the kidney (renal pelvis) and then into the ureter, a narrow tube connecting the kidney to the bladder (show figure 2). The urine collects in the bladder until it passes out of the body through the urethra.

A kidney stone usually forms when substances that are normally found in the urine, such as calcium, oxalate, cystine, or uric acid, are at high levels. However, in some children, stones can also form if these substances are at normal levels. Knowing the stone composition is important as this information may guide therapy (see "Stone testing" below).

The substances form crystals, which become anchored in the kidney and gradually increase in size, forming a kidney stone. Stones that are less than 5 millimeters (0.2 inches) are usually passed without intervention while larger stones usually require treatment.

A kidney stone moves through the urinary tract and, if it is small enough, it will be expelled in the urine. A larger stone may become lodged within the urinary tract, causing pain and sometimes blocking the flow of urine. Occasionally, a stone may not pass into the ureters and can enlarge to fill the entire renal pelvis, which can damage the kidney if it produces infection or obstruction.

SYMPTOMS — The most common symptoms of kidney stones include abdominal or back pain, blood in the urine (hematuria), nausea or vomiting, and the urgent need to urinate. However, some children, particularly young children, do not have any symptoms and the kidney stone is found when an imaging test (eg, x-ray) is done for another reason.

Pain — Pain is the most common symptom of a kidney stone. Pain can range from a mild and barely noticeable ache to intense discomfort. The likelihood that the child will feel pain depends somewhat upon the child's age; adolescents are more likely to have pain than young children.

Typically, the pain waxes and wanes in severity. Waves of severe pain, known as renal colic, can last 20 to 60 minutes, although less severe pain can occur between episodes of renal colic.

The area that is painful depends upon the location of the stone, which may change as the stone moves. The most common areas of pain include the flank (one side of the lower back, show figure 3) and the abdomen. Younger children may not be able to say exactly where they feel pain.

Hematuria — Hematuria (blood in the urine) occurs in 30 to 50 percent of children with kidney stones. The urine may appear pink or red-colored, or the blood may be visible only when the urine is analyzed in a laboratory.

Other symptoms — Other common symptoms include nausea or vomiting, pain with urination, and an urgent need to urinate. Pain with urination and an urgent need to urinate can also occur when a child has a urinary tract infection. An evaluation is needed to distinguish between a urinary tract infection and a kidney stone. However, urinary tract infections are often seen in children with kidney stones. (See "Patient information: Urinary tract infections in children").

RISK FACTORS — Certain factors can increase a child's risk of developing kidney stones.

* History of kidney stones — Children who have had a kidney stone in the past have the highest risk of developing a stone in the future. Children who have one episode of kidney stones are usually advised to follow preventive measures to decrease the risk of developing a stone in the future. (See "Prevention" below).

* Low fluid intake — The amount of fluids a child drinks directly affects the amount of urine that is made. Drinking a small amount of fluids means that less urine is made, which increases the concentration of stone-forming substances in the urine. Increasing fluid intake can reduce the risk of recurrent stones. (See "Increase fluid intake" below).

* Diet high in animal protein — Children who eat a diet with high levels of animal protein (eg, beef, pork, lamb, chicken) may have an increased risk of developing calcium oxalate stones, especially if the child has difficulties with intestinal absorption. However, normal amounts of protein are essential for growth and do not increase the risk of forming kidney stones.

* Ketogenic diet — Diets that include a very small amount of carbohydrates, called ketogenic diets, can increase the risk of kidney stones. Ketogenic diets are sometimes used to treat seizure disorders. (See "Patient information: Treatment of seizures in children").

* Cystic fibrosis — Children with cystic fibrosis are at higher risk of developing kidney stones.

* Urinary tract abnormalities — Anatomic abnormalities of the kidneys or ureters, or difficulties with bladder emptying, increase the risk of developing a kidney stone.

* Medications — Some medications promote formation of urine crystals. These include furosemide, acetazolamide, and allopurinol.

* Inherited disorders — Several uncommon inherited disorders can increase a child's risk of developing kidney stones. Testing for these disorders may be recommended in some cases.

DIAGNOSIS

Urine tests — Two urine tests are recommended for children who are suspected of having a kidney stone. This includes a urine culture, to determine if the child has a urinary tract infection, and a urinalysis, which can determine if microscopic crystals are present in the urine . (See "Patient information: Urinary tract infections in children").

Imaging tests — To confirm the presence of a kidney stone, an imaging test such as a CT scan, ultrasound, or x-ray, is necessary. The imaging test can also help to determine if there are abnormalities of the urinary tract, which would increase the risk for future stones. Computed tomography (CT scan) is the preferred test in most cases.

Computed tomography (CT) scan — A CT scan creates a three dimensional image of structures within the body. A particular type of CT scan (called noncontrast helical CT) can identify almost all types kidney stones (including those that are not seen with the other imaging tests), and can determine if there the stone is blocking (obstructing) the urinary tract (show radiograph 1).

There is some concern about exposing a child to excessive amounts of radiation, especially if the CT scanner uses an adult dose of radiation. In many cases, the amount of radiation can be reduced, based upon the child's size and weight. If this is not possible, another imaging test, such as ultrasound, may be recommended.

Ultrasonography — Ultrasonography (the use of sound waves to visualize body structures) can also be used to detect stones, although small stones and stones in the ureters may be missed. However, ultrasound is the procedure of choice for children who should avoid radiation, such as in pregnant girls or if the dose of radiation in a CT scanner cannot be adjusted for small children.

Abdominal x-ray — Many types of kidney stones can be seen on standard abdominal x-ray (called KUB, kidneys, ureter, bladder). However, certain stones, such as uric acid stones and small stones, may not be seen. As a result, another test, such as a CT scan, may be required if a kidney stone is likely but the abdominal x-ray is negative.

TREATMENT

Treatment at home — If the stone is small, pain is manageable, and the child is otherwise healthy, treatment may be provided at home. Stones smaller than 5 millimeters (0.2 inches) often pass on their own without requiring a procedure, even in young children.

Pain is usually managed with a nonsteroidal antiinflammatory drug such as ibuprofen (Advil®, Motrin®). In addition, the child is encouraged to drink an increased amount of fluids to help flush the stone out of the kidney, ureter, or bladder. (See "Increase fluid intake" below).

The parent/child will be asked to strain the child's urine for a few days, until the stone passes. Urine strainers are available from most hospital supply stores, and are placed under the toilet seat. If a urinary strainer cannot be obtained, a receptacle covered by cheese cloth or a fine mesh sheet can be used.

If a stone or stone fragment is passed, it can be analyzed in a laboratory to determine the type; this can help to guide future treatment. Once the stone is passed, an imaging test (usually ultrasound) of the urinary tract may be performed to confirm that the stone was passed and that no fragments or additional stones remain.

Hospital treatment — In some cases, the child will need to be hospitalized for treatment. The following are the two most common reasons for hospitalization:

* The urinary tract is blocked (obstructed) by the stone, preventing the normal flow of urine. If the obstruction is not treated quickly, it can cause permanent damage to the kidneys.

* The child's pain cannot be controlled because it is severe or because the child is vomiting

In the hospital, the child will be given intravenous (IV) pain medications and IV fluids. If the stone is small, this treatment may be continued for several days, until the stone passes. During this time, the location of the stone is usually monitored with ultrasound and the child's urine will be strained to recover any stone or stone fragments that pass.

However, stones larger than 9 or 10 millimeters (0.4 to 0.45 inches) rarely pass on their own and generally require treatment. Other reasons for treatment include severe pain and obstruction of the urinary tract.

Treatments to eliminate the stone — One or more treatments may be recommended to eliminate a kidney stone. Shock wave lithotripsy is the first-line treatment in most cases.

Shock wave lithotripsy (SWL) — SWL is the treatment of choice in many children, particularly if the stone is located in the renal pelvis or upper ureter.

To pinpoint the location of the stone, an x-ray or ultrasound is performed. A high-energy shock wave is then directed toward the stone; this passes through the skin and body tissues and causes a release of energy at the stone surface. This energy causes the stone to break into fragments that can be passed. The procedure takes about 20 minutes. Some, although not all, children will require anesthesia to prevent movement during the treatment.

Shock wave lithotripsy (SWL) has been shown to be an effective and safe procedure for removing stones in children, including small children and infants. In one study, the overall percentage of children who had no remaining stones after SWL was 73 percent [1]. The success of the procedure depends, in part, upon the size of the stone; larger stones are more difficult to break up and may require more than one treatment. It may take three months for all of the stone fragments to pass.

Percutaneous nephrolithotomy (PN) — Large stones or stones resistant to shock wave lithotripsy may require a minimally invasive surgical procedure to remove the stone, during which the child is given anesthesia to induce sleep and prevent pain. During the procedure, small telescopic instruments are passed through the skin (percutaneously) into the kidney to remove the stone. This procedure may be combined with shock wave lithotripsy.

The percentage of children who have no remaining stones after PN is between 70 and 90 percent, depending upon the experience of the clinician, the size of the stones, and the presence of an underlying abnormality in the kidney, ureter, or bladder.

Ureteroscopy — Ureteroscopy is often used to remove stones obstructing the middle and lower portion of the ureter. Before the procedure, the child is given anesthesia to induce sleep and prevent pain. A small telescopic instrument is passed through the urethra and bladder, into the ureter and kidney. The telescope contains a camera and other instruments, which allows the physician to see the obstructing stone and remove it or to break the stone up into smaller pieces that can pass more easily.

The percentage of children who have no remaining stones after ureteroscopy is approximately 90 percent.

Prognosis — There are inadequate data about the long term prognosis of children who develop kidney stones. The chances of future kidney stones, kidney damage, and other complications depends largely upon the child's age during the first episode of kidney stones and the underlying reason that the stone developed.

PREVENTION — Children who develop a kidney stone have a significant chance of developing stones in the future. Studies have estimated the chances to be between 30 and 65 percent [2]. However, a number of steps can decrease the chance that another stone will develop.