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  • Just a few decades ago, children born with hydronephrosis may not have been diagnosed until they began to show symptoms, if at all. But advances in ultrasound technology mean that today this highly treatable condition—in which urine trapped in the kidney causes it to swell—is often detected during pregnancy, meaning there are a lot of parents out there who are wrestling with the same questions and concerns as you.

    • The urinary system—the kidneys, ureters, bladder and urethra—filters waste from the body and removes it in the form of urine. In hydronephrosis, the outflow of urine is impaired, putting stress on this vital system.
    • Hydronephrosis isn’t a specific diagnosis. Instead, it’s a finding that shows that urine is overfilling the kidney.
    • A number of conditions can cause this backup of urine. Identifying the cause of your child’s hydronephrosis will help determine how we will treat it.
    • The excess urine in your child’s kidney may be caused by a condition that either blocks its flow (obstruction) or allows it to leak backward through the urinary system (reflux).
    • In many children, the cause is never known.
    • In more than half of the cases where hydronephrosis shows up on ultrasound, it resolves itself by the time the baby is born or soon after.
    • In children who have mild or, sometimes, moderate hydronephrosis, kidney function is not harmed.
    • If surgery is called for, there is a very high success rate.

    Regardless of the underlying cause, your doctor will describe your child’s hydronephrosis as being mild, moderate or severe. This is based on how much the kidney is stretched and how much the urinary flow is impaired. Your doctor will also tell you whether it’s unilateral (affecting one kidney) or bilateral (affecting both kidneys).

    Hydronephrosis Children’s Hospital Boston’s approach to hydronephrosis

    At Children’s, our physicians and nurses specially trained in  pediatric urology have extensive experience with hydronephrosis; it’s the most common congenital problem (that is, present at birth) that our urological team treats.

    Hydronephrosis can take many forms and can show up in children at varying ages. In caring for patients across the full spectrum of this condition, what sets Children’s apart are our innovations in two key areas:

    Prenatal care: Founded in 2000, the Advanced Fetal Care Center is one of just a handful of comprehensive fetal care centers in the country. It brings together physicians from more than 20 specialties to provide the finest diagnosis, care and treatment for a woman carrying a baby with a congenital condition, such as hydronephrosis. Read more about our Advanced Fetal Care Center.

    Surgical technique: Ever since 2001, when we became the first pediatric hospital to acquire a surgical robot, Children's has been a leader in robotic-assisted surgery for a variety of conditions, including those that cause hydronephrosis. This high-tech approach can offer less pain and scarring, shorter hospital stays and faster recovery.

    Condition: Reviewed by Alan Retik, MD, © Children’s Hospital Boston, 2010


    Boston Children's Hospital 
    300 Longwood Avenue
    Boston, MA  02115


  • We understand that you may have a lot of questions when your child is diagnosed with hydronephrosis:

    • What is it?
    • What are the treatments?
    • How will it affect my child long-term?

    We’ve tried to provide some answers to those questions here, and when you meet with our experts, we can talk with you more about your child’s specific situation.

    In all children with hydronephrosis, there is a backup of urine that causes the kidney to swell. How far the kidney is stretched, and how much the urinary flow is affected, will indicate how severe your child’s condition is.

    • Mild: Your child usually will not experience symptoms; kidney function will be only slightly affected; and the condition usually resolves itself.
    • Moderate: Your child may have some symptoms, but typically the kidney function will not decrease and the condition itself will not get any worse.
    • Severe: Your child may experience symptoms such as urinary tract infections and pain in his side or abdomen. There is also greater risk for damage to kidney function. But remember, these effects may take months or even years to occur, or may never occur.

    How common is hydronephrosis?

    Hydronephrosis is a relatively common congenital condition (meaning a child is born with it), with some estimates showing it affects about 1 in 500 babies.

    It’s often spotted on routine prenatal ultrasounds—at our Advanced Fetal Care Center, hydronephrosis is by far the most common urinary tract abnormality that we deal with. Less often, it goes undetected until an older child begins to experience symptoms.

    Who is at risk for hydronephrosis?

    While boys are about four to five times more likely to be born with hydronephrosis than girls, there are no known risk factors. It hasn’t been tied to genetic influences, meaning that if you have a child with hydronephrosis it’s not likely that your other children will have it.

    And neither hydronephrosis nor its underlying causes have been linked to anything that parents did during pregnancy. In short, there is nothing you could have done to cause or prevent your child’s condition.

    (Note: Hydronephrosis is not always congenital. It can also develop as a result of injury or other illness, such as kidney stones, but this is very rare.)

    When should I seek medical advice?

    Hydronephrosis is often discovered during routine prenatal ultrasound testing, but not always. If your infant has a urinary tract infection (UTI), it could indicate some kind of obstruction or reflux in the urinary system. However, UTIs can be difficult to spot in infants—in many cases, an unexplained fever is the only sign.

    Older children may have more recognizable symptoms of urinary tract infection: strong urge to urinate, painful urination, cloudy urine, etc. If your child tends to get repeat UTIs, you may want to have him evaluated for possible urinary tract obstruction.

    What complications are associated with hydronephrosis?

    The most common complication of hydronephrosis is urinary tract infection—specifically, kidney infection (pyelonephritis), caused by bacteria spreading from the bladder. In children with a severe form of the condition and/or when it affects both kidneys, complications can include kidney damage, renal enlargement and even kidney failure.


    In Greek, hydronephrosis translates as “water in the kidney.” It describes your child’s condition—a kidney overfilled with urine—but isn’t causing it. Instead, one of a number of other factors is at work here.

    There are two main types of problems that cause hydronephrosis. One is obstruction, where urine is physically prevented from draining out of the kidney. The obstruction, or blockage, can be located at any point in the urinary system, from the kidney down to the urethra. The second is reflux, in which urine flows back up into the kidney.

    Types of obstruction

    • Ureteropelvic junction obstruction (UPJ): A blockage at the point where the kidney joins the ureter (the thin tube that carries urine to the bladder). Usually, this is caused by a narrowing at the top of the ureter.
    • Ureterovesical junction obstruction (UVJ): A blockage at the point where the ureter joins the bladder.
    • Posterior urethral valves (PUV): A congenital condition, found only in boys, in which there are abnormal flaps of tissue in the urethra (the tube that carries urine out of the body) that obstruct the bladder. Also associated with vesicoureteral reflux, below.
    • Ureterocele: A bulge in the ureter that can obstruct part of the kidney and sometimes the bladder.

    Types of reflux

    • Vesicoureteral reflux (VUR): A backwash of urine that happens when the muscles at the junction of the ureter and bladder aren’t working properly, and allow urine to flow back up toward the kidney.

    Other causes

    Hydronephrosis may also be caused by such things as an ectopic ureter (in which the ureter doesn’t connect to the bladder). But in more than half of the children who are prenatally diagnosed with hydronephrosis, the condition resolves itself and the cause is never known.

    Signs and symptoms

    Most babies with hydronephrosis have no symptoms. Older children may also have no symptoms if they have mild or moderate hydronephrosis, and the condition may disappear on its own.

    If your child has moderate to severe hydronephrosis, however, he may experience one or more of the following:

    Symptoms of a urinary tract infection can include a strong urge to use the bathroom, painful urination, cloudy urine, back pain, fever and vomiting.


    Q: How soon can hydronephrosis be seen on a prenatal ultrasound?

    A baby’s kidneys begin to produce urine at about 10 to 12 weeks after conception, but it’s usually not until the fourth month or later that doctors can see signs of hydronephrosis.

    Q: Do I need to ask for a special kind of prenatal ultrasound to check for hydronephrosis?

    No—doctors can look for signs of hydronephrosis and other conditions in routine ultrasounds during your pregnancy.

    Q: What can a prenatal ultrasound tell us about my baby’s condition?

    Ultrasound is extremely useful in detecting signs of hydronephrosis, but remember that fetal tissue is very elastic—which means a swelling in the kidney may look worse on ultrasound than the condition really is. That is why your doctor will keep a close eye on the size of the fetus and the kidneys, as well as the level of amniotic fluid, throughout your pregnancy.

    Q: Can prenatal hydronephrosis pose a serious risk to my baby?

    In very rare cases, the condition will impair the flow of fetal urine to the point that there will be too little amniotic fluid (oligohydramnios). In that case, surgery may be required to drain the urine from your baby’s bladder and allow it to flow into the amniotic sac.

    Q: If my baby has hydronephrosis, will I still have a normal delivery?

    In the vast majority of cases, a finding of hydronephrosis won’t have any effect on either your pregnancy or your delivery.

    Q: After I deliver my child, what happens next?

    Doctors will likely prescribe a small daily dose of antibiotics (amoxicillin) to be taken at least until your child’s first evaluation, within two to three weeks.

    Q: Does this mean my other children will have hydronephrosis?

    No—hydronephrosis doesn’t run in families and has never been linked to anything the parents did during pregnancy.

    Q: Will my child need dialysis because of hydronephrosis?

    No, not if at least one of your child's kidneys is functioning normally.

    Q: I’ve heard a lot about robotic-assisted surgery—can I request that for my child?

    While robotic-assisted surgery can offer a number of benefits over and above traditional surgery, it isn’t recommended for every hydronephrosis patient. If your child needs an operation, your doctor will work with you to decide on the surgical approach best suited for him based on age and the underlying cause of his hydronephrosis.

    Useful medical terms

    Bilateral: affecting two sides. Used to describe hydronephrosis that affects both kidneys.

    Hydronephrosis: a swelling of the kidney caused by excess urine

    Hydroureter: a swelling of the ureter caused by excess urine

    Kidney scan (MAG 3): a nuclear scanning test that helps measure the difference in function between the two kidneys and also estimate the degree of blockage in the urinary system

    Posterior urethral valves (PUV): a congenital condition in which there are excess flaps of tissue in the urethra, obstructing the bladder

    Pyeloplasty: an operation that removes an abnormally narrow portion of the ureter and reconnects the rest to the kidney’s drainage system. One of the most common operations for hydronephrosis.

    Renal: related to the kidneys

    Renal ultrasound (RUS): a kind of ultrasound test that shows the size, shape and position of the kidney

    Unilateral: affecting one side. Used to describe hydronephrosis that affects a single kidney.

    Ureter: a long, narrow tube that carries urine from the kidney to the bladder

    Urethra: the tube through which urine travels from the bladder out of the body

    Urinary system: Made up of the kidneys, ureters, bladder and urethra, it filters waste from the body and removes it in the form of urine.

    Unilateral: affecting one kidney only (common)

    Ureterocele: a bulge in the ureter that can obstruct part of the kidney and sometimes the bladder

    Ureteropelvic junction obstruction (UPJ): a blockage in the urinary system at the point where the kidney joins the ureter

    Ureterovesical junction obstruction (UVJ): a blockage in the urinary system at the point where the ureter joins the bladder

    Vesicoureteral reflux (VUR): an abnormal flow of urine from the bladder back into the ureter and sometimes the kidneys

    Voiding cystourethrogram (VCUG): a type of x-ray that shows the flow of urine through a patient’s bladder and urethra during urination

  • The first step in treating your child is forming an accurate and complete diagnosis. Unlike hemophilia or strep throat, hydronephrosis isn’t a specific diagnosis of disease. Instead, it’s a finding that shows there’s an impairment in your child’s urinary flow that’s making the kidney swell. In diagnosing hydronephrosis, your doctor will search for what is causing that impairment in order to determine the best treatment for your child.

    You may hear your child’s hydronephrosis described as “prenatal” or “antenatal,” and “neonatal” or “post-natal.” These terms refer to when the diagnosis occurred—either in the womb or after birth—and not to different conditions.

    Prenatal testing

    Signs of hydronephrosis may first show up on a routine prenatal ultrasound (sonography). The test transmits high-frequency sound waves into the uterus; the echoes that bounce back are recorded and transformed into an image of your baby. It will show the size and shape of your child’s kidneys, as well as the amount of amniotic fluid; it can also help reveal obstructions in the urinary system.

    However, doctors usually can’t make a precise diagnosis of hydronephrosis right away. This is partly due to the fact that fetal tissue is very stretchy, so a swelling in the kidney may look worse than the condition really is.

    If an ultrasound indicates your child may have hydronephrosis, your obstetrician will monitor your pregnancy more closely and may perform more frequent ultrasound testing to check for any changes over time. While your child is being monitored, your caregivers will take precise measurements of your child and his kidneys, and the level of amniotic fluid surrounding him.

    Post-natal testing

    For newborns and older children, doctors will use some or all of the following tests to help determine the cause and severity of the hydronephrosis:

    • Renal ultrasound (RUS): By focusing on the kidneys, this ultrasound gives a good picture of how serious the hydronephrosis is. This is the first post-natal test your doctor will perform, and will help determine whether further tests are needed.
    • Voiding cystourethrogram (VCUG): This special kind of x-ray is used to check for reflux, a common cause of hydronephrosis; it also can show if there is an obstruction in the urethra. Using a small tube called a catheter, doctors will fill your child’s bladder with a liquid containing iodine. As the bladder fills and your child urinates, the flow of the liquid will be visible on video x-ray images.
    • Renal scan (MAG 3): This is a type of nuclear scanning test that helps measure the difference in function between the two kidneys and also estimate the degree of blockage in the urinary system. After a tiny amount of radioactive material (radioisotope) is injected into your child’s bloodstream, a special camera called a gamma camera is used to take pictures of the kidneys as the radioactive material moves through them, showing how well they are filtering and draining.

    After we complete all necessary tests, our experts meet to review and discuss what they have learned about your child's condition. Then we will meet with you and your family to discuss the results and outline the best treatment options.

  • No parent wants his or her child to be unwell, and hearing that your baby is having trouble with a vital organ like the kidneys can be especially difficult to hear. But at Boston Children's Hospital we view the diagnosis as a starting point: After identifying what is causing your child's condition, we can begin the process of treating your child, so that we may ultimately return him to good health.

    Moreover, if your baby is diagnosed with hydronephrosis, here are a few helpful things to keep in mind:

    • In many of the children who are diagnosed prenatally, the condition disappears spontaneously by the time of birth or soon after.
    • In children who have mild or, sometimes, moderate hydronephrosis, kidney function is not harmed and the condition may resolve over a period of time after delivery.
    • If surgery is called for, there is a very high success rate.

    In only a handful of cases will doctors need to treat a baby while still in the womb, called fetal intervention. In the vast majority of children, treatment occurs after birth: After considering the severity and cause of the hydronephrosis, doctors will decide between observation and surgery.

    Fetal intervention

    In very rare instances, prenatal hydronephrosis is so severe that it puts the life of the fetus at risk. This usually means there is a dangerously low amount of amniotic fluid (a condition called oligohydramnios) and the obstruction is in the child's urethra, blocking drainage of the bladder and both kidneys.

    The most reliable fetal intervention is a procedure similar to amniocentesis. Guided by ultrasound, surgeons pass a shunt (a small tube) through a large needle inserted into the mother's abdomen and directly into the baby's enlarged bladder. The shunt allows the urine trapped in the bladder to drain into the amniotic sac.

    Even after fetal intervention, however, the child will likely still need some kind of surgical treatment after birth to allow bladder drainage and protect kidney function.


    If post-natal testing shows your child has mild to moderate hydronephrosis, your doctor may opt to wait and see if it will go away on its own. Your child may receive a low dose of antibiotics to prevent infection, and come in for ultrasounds at 6- to 12-month intervals to see if there has been any change in his condition.

    Observation has become the accepted method of treatment in children with mild hydronephrosis. Even in children with moderate hydronephrosis, if kidney function is not lost and kidneys are growing well, observation can provide the chance for the condition to resolve itself.


    Typically, surgery is needed only in severe hydronephrosis, although it may be an option for some children with a moderate condition. The goal of the operation is to reduce the swelling and pressure in the kidney by restoring the free flow of urine.

    The surgical procedure you'll most often hear about is pyeloplasty, which repairs the most common type of blockage that causes hydronephrosis: ureteropelvic junction obstruction (UPJ). In pyeloplasty, the surgeon will remove the narrowed or obstructed part of the ureter and reconnect the healthy portion to the kidney's drainage system. After surgery, children usually stay in the hospital for about three days and heal in about two to three weeks; the success rate is about 95 percent. 

    But there are other surgical treatments your child may undergo, depending on what's causing his hydronephrosis and how severe it is. To learn more about these, see the Children's treatment sections for the following: ureterovesical junction obstruction, vesicoureteral reflux, posterior urethral valves and ureteroceles.

    Robot-assisted surgery

    A nationally recognized pioneer in robotic-assisted surgery, Children's was the first pediatric hospital to use a surgical robot, beginning in 2001. In late 2009 we also became the first pediatric hospital to acquire the latest in surgical robot technology, the fourth-generation da Vinci Si HD System. Children's surgeons use this innovative tool for many procedures, and in fact, perform more pediatric robotic surgeries than any other hospital in the world.

    Among these procedures is one commonly used to treat hydronephrosis: pyeloplasty. About half of the pyeloplasties that Children's surgeons perform, in fact, are done with a surgical robot.

    A robot-assisted pyeloplasty is a laparoscopic (minimally invasive) procedure, meaning surgeons operate with the aid of a tiny camera and very thin instruments inserted into three or four small incisions. Though it takes longer to perform than open surgery, robot-assisted pyeloplasty accomplishes the same goal: removing an obstructed section of the ureter and reattaching the healthy portion to the kidney's drainage system. It can also offer a number of benefits, including:

    • Less post-operative discomfort
    • Smaller scars
    • A shorter post-op hospital stay—usually 24 to 48 hours
    • Quicker recovery and an earlier return to full activities

    Note: Even if pyeloplasty is recommended for your child, a robot-assisted laparoscopic procedure may not be suitable. Right now, this technique is used mostly for school-aged children or older. However, with the development of ever-smaller surgical instruments, the innovators at Children's are envisioning applying it to younger children—even down to six months of age—someday in the future.

    Coping and support

    We understand that you may have a lot of questions when your child is diagnosed with hydronephrosis. Will it affect my child long term? What do we do next? We've tried to provide some answers to those questions on this site, but there are also a number of other resources to help you and your family through this difficult time.

    Patient education: From the office visit to pre-op to the recovery room, our nurses will be on hand to walk you through your child's treatment and help answer any questions you may have—How long will I be separated from my child during surgery? What will the operating room be like? They will also reach out to you by phone, continuing the care and support you received while at Children's.

    Parent to parent: Want to talk with someone whose child has been treated for hydronephrosis? We can often put you in touch with other families who have been through the same procedure that you and your child are facing, and share their experience.

    Social work: As part of Children's broader social work program, our pediatric urology department has a dedicated professional who has helped many other families in your situation. We can offer counseling and assistance with issues such as coping with your child's diagnosis; dealing with financial difficulties; and finding temporary housing near the hospital if your family is traveling to Boston from another area.

    On our For Patients and Families site, you can read all you need to know about:

    • getting to Children's
    • accommodations
    • navigating the hospital experience
    • resources that are available for your family

    In addition, there are two leading national groups that provide additional information on hydronephrosis and/or its underlying causes, and may even be able to connect you with parents across the country.

    • The National Kidney Foundation: This major volunteer nonprofit is dedicated to improving the health and well-being of anyone affected by kidney disease, preventing kidney and urinary tract diseases and promoting organ transplantation.
    • The American Association of Kidney Patients: “Founded by kidney patients for kidney patients,” this nonprofit works to educate and improve the well-being of people with kidney ailments.
    Integrative therapies

    Our patient-centered approach means that we want your child to not only get better, but also feel good along the way. Throughout the hospital, you¹ll find clinicians trained in therapies that can make your child feel more comfortable, learn to shift focus away from pain and enjoy some peaceful moments during what may be an anxious time. Read more about how acupuncture, guided meditation, guided imagery, massage, Reiki and therapeutic touch could help your child.

  • In addition to leading the way in the use of robotic surgery, Children’s Hospital Boston is continually working toward faster, more accurate diagnoses and more effective treatments for children with urologic disorders. Among the recent areas of research that our urology department has conducted, several hold great promise for improving the lives of children with hydronephrosis.     

    Finding the genetic markers of vesicoureteral reflux (VUR): One of the more common causes of hydronephrosis, VUR has long been difficult for physicians to manage and often frustrating for parents because there is currently no way to detect which children are at risk for the persistent—and often damaging—form of this condition.

    Moreover, to diagnose VUR, physicians must pass a catheter up the urinary tract into the bladder. But Children’s researchers aim to replace that procedure with a simple genetic test, as well as possibly offer a way to predict which patients have VUR that will not resolve on its own.

    Using proteins to target kidney obstruction: A team led by Dr. Richard Lee is studying proteins in the urine in a quest to identify illnesses at an earlier age. Specifically, the team hopes to be able to predict risk for VUR—a common cause of hydronephrosis—and detect changes in the bladder tissue that may tell them whether a child’s hydronephrosis is getting worse.

    Making advances in fluorescent imaging: Recent developments in fluorescent (molecular) imaging have given physicians a potentially more accurate alternative to ultrasound and x-rays when looking at the urinary tract. Research by Hiep Nguyen, MD, shows that by using fluorescent imaging to see a child’s live urinary flow, physicians may be able to work faster and more accurately in diagnosing ureterovesical junction obstruction (UVJ), a common cause of hydronephrosis. Moreover, it may help surgeons better visualize the obstruction when operating on a child with UVJ.

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