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What is a kidney stone?

Kidney stones are small, hard deposits of mineral and acid salts formed within the urinary tract, which can obstruct the drainage of urine and may cause intense pain. While kidney stones are still relatively uncommon in children, the number of cases is growing.

There are many different kinds of stones. The most common types are:

  • calcium oxalate stones
  • calcium phosphate stones

Most of the time, stones are found in the kidney or ureter (the tube that connects the kidney with the bladder). Many stones pass all by themselves, without treatment. Others will need to be removed, which can often be done using a noninvasive method.

What are the symptoms of kidney stones?

Some children with kidney stones have no symptoms. These stones are still in the kidney and have not moved to the ureter and are called “silent stones.” Other children can experience severe pain due to urinary obstruction. Common symptoms of kidney stones include:

Kidney stones can affect different children in different ways. Young children in particular may have vague symptoms that can make diagnosis challenging.
Any child with pain accompanied by blood in the urine — even if it’s just a little bit — should be evaluated by a doctor.

What causes kidney stones?

Kidney stones form when a child has too much of the minerals that make up the stone and not enough water in their urine. This can occur either because there is an abnormally high mineral content in the urine, or the urine is too concentrated because of dehydration.

Some rare stone diseases can result from inborn metabolic problems, which means that the child has a genetic condition that causes their body to make these stones. A family history of kidney stones predisposes other members of the family to have stones, although how these tendencies are passed from one generation to the next is not well understood.

Children who can’t move for long periods of time (in traction after surgery, for example) may also be susceptible to stones. This is because bones that are inactive can’t regenerate themselves properly, which results in calcium being flushed into the system.

How we care for kidney stones at Boston Children’s Hospital

At Boston Children’s Hospital, we treat children with kidney stones in our dedicated Kidney Stone Program. We see children who have had kidney stones and those who are at risk for developing them. Your child will see both a pediatric urologist and a pediatric nephrologist at the same appointment. This multidisciplinary team approach allows us to optimize your child’s care and work together to develop a treatment plan.

We treat stones in several ways, depending on their size, location, number, and composition. In nearly all children, we can use noninvasive or minimally invasive surgical techniques. In rare instances, we use robotic surgery techniques to remove the stones.

The best treatment is prevention. Your child will receive a metabolic evaluation to determine if they have risk factors for future kidney stones. We then prescribe individualized treatment plans to prevent new stones from forming, and we monitor your child with urine and blood tests and sometimes ultrasound exams.

Kidney Stones | Diagnosis & Treatments

How are kidney stones diagnosed?

The first step in treating your child is forming an accurate and complete diagnosis. Our doctors can tell if your child has a kidney stone by looking at their urinary tract with an ultrasound or a CT scan. Ultrasound is our first diagnostic choice because it doesn’t expose your child to radiation.

If the ultrasound is inconclusive — or if your child’s doctor has any questions about it — we might do a CT scan. A CT scan can help your child’s doctor locate the exact position and size of the stone for surgical planning.

During your appointment, you and your child will meet with a pediatric urologist and a pediatric nephrologist for a physical exam and discussion of your child’s health, including a review of current prescribed and over-the-counter medications, and a detailed history of your child’s diet and fluid intake.

If your child passes a stone, you should try to recover it, place it in a plastic bag, and bring it to your appointment so that it can be sent out for chemical analysis. We will also perform several tests during the visit, including:

  • analysis of urine to assess for factors that contribute to stone formation, such as increased levels of calcium in the urine
  • blood tests to look for other risk factors
  • chemical analysis of the stone (if it has passed or has been removed) to identify the type of stone and provide important clues about why it formed
  • evaluation for inherited disorders to look at risk factors (such as rare inherited disorders)

Once these tests are completed, you may be asked to return for a follow-up appointment.

How are kidney stones treated?

Treatment plans are based on the cause of the stones, but your child's doctor may prescribe high fluid intake and a low-salt diet to reduce the chances of kidney stone recurrence. The nephrologist may prescribe medications to help prevent stones from forming, such as medications that lower the levels of calcium in the urine or other medications that help substances to dissolve in urine.

If your child has an inherited condition that leads to kidney stones, doctors will create an individualized plan of care based on the nature and symptoms of the disorder. These conditions include cystinuria, primary hyperoxaluria, Dent disease, and other conditions that may increase stone risk.

The best treatment will depend on the size, location, number, and composition of your child's stone. In many cases, stones can pass spontaneously without any treatment — in fact, children can pass stones that are relatively large compared to those that adults can pass. Your child's doctors may prescribe certain medications that have been shown to increase the chance of a stone passing spontaneously.

Sometimes it is necessary to remove the stones, depending on your child's condition and symptoms. We may also consider removing a growing stone even if it is causing no symptoms, rather than waiting until it is very large. The choice of technique depends upon the location, size, and type of stone, as well as your child's anatomy. Methods include the following:

Extracorporeal shock wave lithotripsy

Extracorporeal shock wave lithotripsy (ESWL) is the most common and least invasive way of treating stones. ESWL uses a special machine called a lithotripter to send shock waves through the skin into your child's body.

The lithotripter focuses the shock waves at the precise point where the stone is located, in much the same way that a magnifying lens can focus sunlight to create intense heat. This causes the stone to break into small fragments. The lithotripter applies many shock waves — often several thousand — slowly, which may take up to an hour. The pieces will then pass in the urine over the following days.

When the shock waves enter the skin, they are not focused, so they do no damage to your child’s skin or internal organs. However, there can be some discomfort with this procedure, and it is very important that your child remain still during the procedure so that the shock waves can be accurately targeted. For this reason, we use general anesthesia for this procedure.

After treatment, it may take up to three months for all fragments to pass, depending upon the position of the stone. The overall success rate of ESWL is about 85 percent. Stones in the lower pole of the kidney are less likely to pass. Very hard stones, such as those made of cystine or certain kinds of calcium stones, may not fragment very well.

Ureteroscopy

This technique uses a small scope passed up through the urethra into your child's bladder, and from there up into one or both ureters (the tubes that connect the kidney with the bladder) and kidneys. Digital cameras attached to the scope allow doctors to see the stones and remove them with a variety of specially designed instruments.
Ureteroscopy is done under general anesthesia. The success rate is very high — upwards of 95 percent. However, success rates are lower for large stones, which may require multiple treatments, and in children whose urinary anatomy makes it difficult to get the scope up to the stone.

Percutaneous nephrolithotomy

Percutaneous nephrolithotomy (PCNL) is used to treat large kidney stones. It uses a needle that goes through your child’s skin and into their kidney, under ultrasound or x-ray guidance. An instrument is then passed into the kidney to allow direct examination, fragmentation, and removal of the stone.

PCNL is done under general anesthesia. A kidney-drainage tube is usually left in place for two to four days. PCNL is particularly useful if your child has a hard or large stone that might not fragment with ESWL or has abnormal kidney anatomy. A special, small-access sheath permits access to the kidney for stone removal in small children.

Open stone surgery

Years ago, almost all stones required open surgery for removal. However, with advances in technology, most stones can now be treated with a less invasive approach. Occasionally, open stone surgery is still needed in children with unusual anatomy or other specific conditions.

How can my child prevent kidney stones?

Effective prevention depends largely upon why the stones are forming. Your child’s doctors will conduct a metabolic evaluation to identify risk factors for stone formation. After this metabolic evaluation is completed, your doctor will better understand what is causing the stones — and how best to prevent your child from developing more stones. Sometimes, medications are required to help prevent future kidney stones. The following tips can also help:

Encourage your child to drink plenty of water, not only when they are thirsty, but also through the day. Keeping hydrated is extremely important. An excellent way to determine if your child is properly hydrated is by checking the color of the urine; if it's clear, they are adequately hydrated. If urine is yellow, they are dehydrated.

Many sport drinks have added sodium, so be sure to check the label before drinking them and avoid drinks with high amounts of sodium. Water is always the best way to stay hydrated and decrease your child's chances of developing stones. Citrate is generally good to have in the urine. We encourage children to drink lemonade (made with real lemon juice) because it may be a source of natural citrate.

Avoid salty foods like chips, French fries, processed meats, canned soups, prepackaged meals, and high-fat items. To cut salt intake, leave the saltshaker off the kitchen table and do not add salt to food while cooking. Focus on providing a healthy diet high in fruits and vegetables, and be sure to include the recommended daily allowance (RDA) of protein, calcium, and vitamin D.

Exercise, exercise, exercise. Although fit children can develop kidney stones, many experts believe obesity may be related to higher incident rates. Make sure your child keeps hydrated while exercising. If there is a family history of kidney stones, pay extra attention to diet, exercise, and water consumption.

Do NOT cut back on calcium in your child’s diet, unless your doctor recommends this. Many people assume that since kidney stones are made of calcium, they can reduce stone formation by reducing calcium in the diet. However, calcium is an essential nutrient (especially for children), and the body’s processing of calcium is extremely complicated, so reducing formation of calcium kidney stones is not as simple reducing calcium intake. We generally recommend our patients receive the RDA for calcium and vitamin D in their diet. This should be discussed with your doctor.

Kidney Stones | Programs & Services