Wednesday, July 8, 2009

Hydronephrosis? What is That?

Hydronephrosis is dilation or stretching of the area of kidneys where urine collects that can occur when there is an obstruction of urine flow somewhere along the urinary tract, most often in the upper section.

Normally, urine flows from the kidneys down through the ureters and into the bladder. But, if there is some kind of a blockage that prevents urine from draining properly into the bladder or out of the bladder, the kidney overfills with urine and hydronephrosis occurs. The blockage may be partial, letting urine pass, but at a slower rate and with increased pressure.

Another cause of hydronephrosis is vesicoureteral reflux, when urine that dwells in the bladder flows back into the ureters and often back into the kidneys. Most children with hydronephrosis are born with the condition although it can develop during childhood. It is the most common urinary tract anomaly (abnormality) and ranges in severity. In mild hydronephrosis, the pelvic (the part of the kidney that collects the urine) dilation is barely noticeable, whereas in severe hydronephrosis the swelling occupies much of the abdomen

Facts about hydronephrosis
It is four to five times more common in males than females.
It can occur in one or both kidneys.
Most mild cases and even some moderate cases may resolve on their own. More severe cases may require surgery.

What causes hydronephrosis?

There are many different kinds of urinary tract obstructions that lead to hydronephrosis, but the most common type is found where the ureter joins with the kidney, an area known as the ureteropelvic junction. (See ureteropelvic junction obstruction.) A blockage at this juncture is usually due to an abnormal narrowing at the top of the ureter. The second most common site of obstruction is at the ureterovesical junction (the position where the ureter joins with the bladder). Other types of blockage may be at the junction of the ureter with the bladder or in the urethra which empties the bladder. A condition that may appear similar to an obstruction by causing hydronephrosis in some children is vesico-ureteral reflux (a backwash of urine from the bladder).

It is unknown why some babies are born with the kinds of anomalies that lead to hydronephrosis. Neither hydronephrosis nor its causes have ever been linked to anything the parents did during pregnancy. Not all children with hydronephrosis are born with it. Hydronephrosis can, for example, rarely develop as a result of stones or after an injury to the urinary tract or previous surgery

What are the symptoms of hydronephrosis?
In mild cases and even some moderate cases of hydronephrosis, children will have no symptoms and the condition may disappear on its own within the first year of life. In more severe cases, when kidney function is affected, the infant or child can experience pain, bleeding and infections. These symptoms may not develop until months or years after hydronephrosis is first detected

How is it diagnosed?

Hydronephrosis may first be discovered on a routine prenatal ultrasound. Hydronephrosis is not a specific diagnosis, but a finding that indicates an obstruction. In diagnosing hydronephrosis, doctors search for the cause of the obstruction, which dictates the appropriate treatment.

In most cases, if hydronephrosis is detected on a prenatal ultrasound, you will be referred to a pediatric urologist for further evaluation and a more detailed ultrasound. Usually, a precise diagnosis cannot be made right away. Your pediatric urologist may want you to be monitored periodically to note any changes that occur over time, providing further evidence of a particular diagnosis or risk of affecting kidney function. While you are being monitored, doctors will be taking precise measurements of the fetus, fetus' kidney and the level of amniotic fluid.

At some point, the hydronephrosis will be classified as either mild, moderate, severe unilateral (occurring in one kidney) or bilateral (occurring in both kidneys.) Based on these classifications, the urologist will look for clues of any urinary tract anomalies that could cause the hydronephrosis. Here are some examples of more common conditions responsible for hydronephrosis, but virtually any type of blockage can be responsible:

Ureteropelvic junction obstruction (obstruction where kidney and ureter meet) - signs can include swelling of pelvic region without any swelling of the ureter.

Vesico-ureteral reflux (backwash of urine) - signs include a varying degree of hydronephrosis during one ultrasound evaluation or between exams.

Posterior urethral valves (abnormal flaps of tissue in the urethra) - ultrasound findings can include bladder distention, bilateral kidney and ureteral dilation, and sometimes, decreased amniotic fluid level (oligohydramnios).

Ectopic ureter (abnormal flaps of tissue in the urethra) - signs include hydronephrosis of the ureter and usually the upper part of the kidney.

Ureterocele (a cystic or balloon-like end of the ureter in the bladder that obstructs the ureter and may obstruct the bladder) - signs include a cystic structure in the bladder associated with hydronephrosis of the ureter and usually the upper part of the kidney.

If a diagnosis is not made prior to birth or if a child develops hydronephrosis, doctors will use a combination of the following tests on your newborn or child, depending on the severity of the problem, to help determine the underlying cause:

Voiding cystourethrogram (VCUG) - a specific X-ray that examines the urinary tract. A catheter (hollow tube) is placed in the urethra (tube that drains urine from the bladder to the outside of the body) and the bladder is filled with a liquid dye. X-ray images will be taken as the bladder fills and empties. The images will show if there is any reverse flow of urine into the ureters and kidneys and how well the bladder empties. It is also used to determine if there is obstruction in the urethra.

Renal ultrasound (RUS) - a non-invasive test in which a transducer is passed over the kidney, producing sound waves which bounce off the kidney and transmit a picture of the organ on a video screen. The test is used to determine the size and shape of the kidney, and to detect a mass, kidney stone, cyst, or other obstruction or abnormalities.

Intravenous polygram (IVP) - a special x-ray of the kidneys, ureters and bladder that involves injection of a contrast agent that fills the urinary tract on the x-ray and helps the doctor to see the organs. The IVP shows how well the kidneys drain urine.

A renal (kidney) scan (MAG 3 with lasix) - This scan provides very sensitive quantitative information regarding kidney function and drainage characteristics. Along with the IVP, it is particularly helpful in identifying and assessing the degree of blockage.

How is hydronephrosis treated?

Treatment depends on the severity and cause of the hydronephrosis. Children with mild hydronephrosis caused by mild obstructions may simply be monitored by renal ultrasound and VCUG and receive no treatment, as the problem is likely to correct itself. Infants will probably undergo these imaging tests at around 2-3 months of age.

If doctors find moderate to severe hydronephrosis, severe unilateral hydronephrosis or severe bilateral hydronephrosis during the prenatal ultrasound, your child will receive antibiotics during the first days after birth. At one to three months of age, depending on the severity of the hydronephrosis, your child will undergo imaging studies to confirm the cause and determine if surgery is needed.

Surgery is usually needed to correct the problem only in severe unilateral or severe bilateral hydronephrosis, although it may be considered in some moderate cases. Surgery relieves the obstruction or reflux causing hydronephrosis. For descriptions of surgical treatments used to correct specific conditions causing hydronephrosis, see treatment sections for the following entries: ureteropelvic junction obstruction, ureterovesical junction obstruction, vesicoureteral reflux or posterior urethral valves.



The parts of the kidney(s) that are widened in hydronephrosis are the renal calyces and renal pelvis. The word "renal" refers to the kidneys. The renal calyces are narrow tubes that carry urine from the kidneys to the renal pelvis. The renal pelvis is a funnel-shaped opening that drains urine from the renal calyces to the ureters.

The ureters are two thin, tube shaped structures that connect to the kidneys and carry urine to the bladder. One ureter is attached to each kidney. The bladder is a stretchable structure in the body that holds urine. Urine travels from the kidneys to the renal calyces, then to the renal pelvis, then to the ureters, then to the bladder, and then to the urethra where it is drained outside of the body. The urethra is a tube shaped structure in the body that drains urine from the bladder. The kidneys, ureters, bladder, and urethra make up the urinary tract.


Hydronephrosis is not a disease. Rather, hydronephrosis is a physical consequence of a disease that causes the urine to have difficulty draining out of the kidneys, ureters, and bladder.


Unilateral hydronephrosis is hydronephrosis that affect one kidney. Bilateral hydronephrosis is hydronephrosis that affects both kidneys.


Signs and symptoms of hydronephrosis can vary, depending on whether the condition occurs suddenly or develops slowly over a period of time. If hydronephrosis occurs suddenly, the person may experience severe back pain.

If hydronephrosis develops slowly over a period of time, it may not cause any signs or symptoms until the ureter is completely blocked and kidney failure results. If the kidney becomes infected, it can become filled with pus and lead to a fever. Pus is a yellow or green creamy substance sometimes found at the site of infections.

General signs and symptoms of hydronephrosis include pain in the sides, a mass in the belly, very high fever, blood in the urine, nausea, vomiting, and a high number of white blood cells in the urine. White blood cells help protect the body against diseases and fight infections. In the newborn, an infection of the urinary tract is a sign that some type of blockage in the kidney is present that may lead to hydronephrosis. In older children, repeated infections of the urinary tract may reflect a blockage of the kidney.

Feeling a frequent urge to pee and peeing very often are other signs and symptoms of hydronephrosis. Painful and burning sensation while peeing is another symptom of hydronephrosis that is usually caused by an infection of the urinary tract. It should be noted that in many people, there are no signs or symptoms of a blockage in the urinary tract. This is especially true for children with mild hydronephrosis.


In hydronephrosis, the kidneys become widened with urine (pee) that cannot pass by a blockage or narrowing. The blockage or narrowing is usually in the ureter or urethra, but can also be in the bladder. Blockages can occur at the uretovesical junction, which is where the ureter meets the bladder. Since the urine has difficulty getting past the blockage, it backs up into the kidney and becomes trapped. This causes areas inside the kidney to stretch. The blockages can occur suddenly or slowly over time. In infants with this condition, the areas inside of the kidney may appear very wide because the infant's tissues are stretchier than adults

There are many possible reasons why the structures mentioned above can become blocked or narrowed. One reason is the formation of stones in the kidney (known as kidney stones). Another reason is the formation of scar tissue in the ureter or urethra. A blockage where the bladder connects to the urethra can lead to hydronephrosis. This type of blockage is known as bladder outlet obstruction.

A tumor in the kidney or other parts of the urinary tract can cause blockage of the ureter(s). Tumors are abnormal masses of tissue that form when cells in a certain area of the body reproduce at an increased rate. Tumors outside or in back of the peritoneum can lead to hydronephrosis. The peritoneum is a layer of tissue that lines the belly and covers most of the organs in the belly.

As was mentioned earlier, the widening in hydronepohrosis is most common at the point where the renal pelvis connects with the ureters (known as the uretopelvic junction). A blockage in the area where the renal pelvis connects with the ureters can cause widening in this area to occur. A blockage in this area is known as a uretopelvic junction obstruction. A uretopelvic junction obstruction usually develops in the first four months that a mother is pregnant, in children born with this type of blockage.

The presence of abnormal folds in a specific part of the urethra can lead to hydronephrosis. This condition is known as posterior urethral valves. Also, fibrosis of structures behind the peritoneum and of connective tissue that often makes up the ureters can lead to hydronephrosis because it can cause the ureters to be blocked. Fibrosis is an overgrowth of scar tissue or connective tissue. Connective tissue is any tissue that surrounds and supports specialized structures in the body.

Displacement of the kidneys from its normal position can lead to hydronephrosis as can pressure from adhesions outside of the urinary tract. Adhesions are fibrous types of tissue that join body parts that are normally unconnected. Fibrous tissue is a type of connective tissue.
Sometimes, the kidney may contain many cysts, which can lead to hydronephrosis. A cyst is an abnormal lump, swelling, or sac that contains fluid, a part solid material, or a gas, and is covered with a membrane. A blood clot can also lead to a blockage of the ureters and cause hydronephrosis. A blood clot is a collection of a mass of blood.

Pressure from abnormal arteries in the kidneys can lead to hydronephrosis. An artery is a blood vessel that carries blood away from the heart. Aneurysms of the arteries of the kidney are one type of abnormality that can lead to hydrnephrosis. An aneursym is a weakening of the wall of a blood vessel, causing it to expand like a balloon, sometimes leading it to burst.

Neurogenic bladder can lead to hydronephrosis. Neurogenic bladder is dysfunction of the bladder that is caused by damage in the nervous system (the system of nerves in the body). Neurogenic bladder is characterized by retaining or emptying too much urine.

Another cause of hydronephrosis is an enlarged prostate gland. The prostate is a organ near the bladder that produces a fluid that is part of semen. Semen is a fluid that is discharged from a male's penis in order to reproduce with a female. If the prostate is enlarged, the fluid that it produces can be blocked, which would cause the urine in the bladder to be under pressure.
Cancer of the prostate gland can cause blockage that leads to hydronephrosis. Cancer is an abnormal growth of new tissue characterized by uncontrolled growth of abnormally structured cells that have a more primitive form. One type of cancer in the prostate that can lead to hydronephrosis is a carcinoma.

A carcinoma is any malignant cancer that arises from cells in the covering surface layer or membrane (outer covering) that lines an organ of the body. When describing cancer, malignant means that the newly formed tissues are made of abnormally structured and primitive-looking cells that grow uncontrollably, spread throughout the body, and invade surrounding tissues.
Vesicouretal reflux is another possible cause of hydronephrosis. Vesicouretal reflux is a backward flow of urine from the bladder into the ureter, when the bladder fills or empties.

The urine can also flow black into the renal pelvis. This condition is caused when the valve between the ureter and bladder does not function. A valve is a natural structure or man-made device in a passageway, tube, vessel, or hollow organ that allows fluid or partly fluid contents to travel in one direction, but closes to prevent the flow of those contents in the opposite direction.
About 75% or people with vesicouretal reflux outgrow this condition during childhood. However, many children will need to be treated with antibiotics to prevent kidney damage before outgrowing the condition.

Edema that is caused by an infection of the urinary tract can lead to hydronephrosis. Edema is an abnormal buildup of too much watery fluid in the cells, tissues, and or openings inside the body. Pregnancy can cause changes in the urinary tract that lead urine to be backed up, which can cause hydronephrosis.

A condition known as prune-belly syndrome is associated with hydronephrosis. In prune belly syndrome, certain muscles in the belly are missing, the kidneys are small and abnormally developed, the testicles do not drop down, and the ureters and bladder are usually greatly enlarged. The condition is called prune-belly syndrome because the belly sticks out and is wrinkly like a prune.

There are several disorders of the muscles, brain, and/or spinal cord that can lead to hydronephrosis, such as paraplegia, tabes dorsalis, spina bifida, and multiple sclerosis. Paraplegia is a loss of the ability to move and/or feel both legs and generally, the lower trunk (stomach area and lower back). Tabes dorsalis is damage to the spinal cord due to infection from the sexually transmitted disease, syphilis.

Spina bifida is a birth defect in which part of the bones that surround the spinal cord do not form properly, leaving part of the spinal cord exposed. Multiple sclerosis (MS) is a condition in which multiple areas of abnormal patches (known as plaques) develop in the brain and/or spinal cord (depending on the stage of the illness).

Sometimes, in adults and children, the ureters can become narrowed at the area of the renal pelvis with no apparent cause. In some children with hydronephrosis, there is no blockage that is apparent. Some of these cases may be due to abnormal smooth muscle in the renal pelvis or ureter, which causes these areas to widen.

A rare cause of hydronephrosis can occur when there are two ureters collecting urine from a single kidney. In 99% of people, there is one ureter that collects urine from each kidney. In the 1% of people that have 2 ureters for one kidney, a uterocele may be present which causes hydronephrosis. A uterocele is a balloon-like blockage at the end of one of the ureters.


It is estimated that one in 100 people have hydronephrosis affecting one kidney. Less people have hydronephrosis affecting both kidneys. In approximately 2% of all ultrasounds performed before the child is born, hydronephrosis is detected. The cases detected in this manner are usually males.


Hydronephrosis is diagnosed with an ultrasound of the kidneys or belly, especially in unborn children. An ultrasound is a procedure that uses types of sound waves to produce images of the body. The ultrasound used to diagnose hydronephrosis will produce a picture of the kidneys and the ureters. An ultrasound can detect hydronephrosis in an unborn child as early as the first three months that the mother is pregnant. It will be able to show blockages that are causing hydronephrosis as well as many of the other causes described above, such as uretopelvic junction obstruction, posterior urethral valves, and prune belly syndrome.

Another technique used to diagnose hydronephrosis is an intravenous pyelogram. An intravenous pyelogram (commonly abbreviated as IVP) is a technique in which x-rays are used to take pictures of the urinary tract, after a liquid substance called contrast is injected into a vein (a blood vessel that caries blood to the heart). X-rays are a type of radiation, which is a form of energy. To better distinguish between organs, a liquid substance called contrast is used that x-rays cannot pass through. Contrast helps to form an artificial distinction between organs in the body so that the doctor can tell them apart.

Other techniques that can be used to diagnose hydronephrosis are retrograde pyelography and cystoscopy. A retrograde pyelography is another visualization technique that uses x-rays to examine structures in the kidneys after a contrast material has been injected into the ureters and renal calyces. A cystoscopy is a direct examination of the urinary tract by inserting a viewing tube into the ureter.

A renal (kidney) scan is also used to diagnose hydronephrosis in some cases. A renal scan (also known as a flow and function scan) is a technique in which detailed pictures are produced after a radioactive substance is injected into the body, which provides information about kidney functioning. A radioactive substance is a substance that sends out radiation (a type of energy).

The kidney filters this radioactive substance, which is detected by the scanning procedure.
The renal scan will be able to detect differences in functioning between the right and left kidney. It can estimate the size of a blockage that is present and how well the urine is draining out of the kidney. A small tube is inserted in the bladder to keep it empty. Renal scans are usually not performed until one month after birth for the most accurate results.

A CT scan of the kidneys or belly can be used to diagnose hydronephrosis. CT (computerized tomography) scanning is an advanced imaging technique that uses x-rays and computer technology to produce more clear and detailed pictures than a traditional x-ray.

An MRI (Magnetic Resonance Imaging) scan can also be used to diagnose hydronephrosis. MRI scans produce extremely detailed pictures of the inside of the body by using very powerful magnets and computer technology. MRI scans are more detailed, but more expensive than CT scans.

A cystourethogram can be used to help determine if the cause of hydronephrosis is vesicourethral reflux. A cystourethogram is an examination of the urethra and bladder after a contrast substance is injected inside the body. Remember that contrast is a liquid substance that helps to form an artificial distinction between organs in the body so that the doctor can tell them apart. The contrast is passed into the child's bladder through a small tube inserted in the child's urethra.


There is currently no accepted method for how all children with hydronephrosis should be treated. This is because there is presently no way to predict which cases will go away on its own and which will require surgery to remove the blockage. Thus, doctors may differ in their opinion as to whether surgery should be performed or whether the child should be monitored over time. Most doctors today, however, are choosing to observe the child over time (even in moderate to severe cases) before opting for surgery.

In most cases, no specific changes need to be made in caring for the unborn child that is diagnosed with hydronephrosis. Rather, the hydronephrosis and kidney growth of the unborn child will need to be monitored closely as it develops. Another ultrasound is usually done the third day after the child is born to monitor the situation. Repeat ultrasounds may be performed every three months. The condition will likely continue to be monitored (without surgery) if it seems to be improving and if no blockages are seen.

The cause of hydronephrosis is what is treated. Treatment will differ depending on the cause. If the ultrasound (see earlier section) reveals a blockage and the kidney is at least somewhat healthy, the blockage may be removed or decreased by surgery. After surgery, the kidney resumes normal functioning shortly.

The surgery mentioned above usually involves removing the blocked part of the ureter and reconnecting the healthy part of the ureter to the kidney. This type of surgery is known as a pyeloplasty. After the surgery, the child is in the hospital for 3 to 5 days. This type of surgery is successful in about 90 to 95% of the cases. Thus, the surgery is generally safe and effective.
In some patients, a rod-like or thread-like device known as a stent is placed in the ureter. The stent will widen the ureter and help urine get through any blockages that are there. In other patients with a blockage in the ureter, a nephrostomy tube can be used. A nephrostomy tube is a tube that is placed in the kidney, which bypasses (goes around) the ureter, and drains it through the back.

However, some doctors prefer to observe the child for a given period of time and hold off on surgery, since the condition may go away by itself without the risks of surgery. Doctors are more likely to hold off on surgery in cases where it does not appear kidney functioning is declining and that the kidneys are growing normally

Antibiotics are used to prevent and treat urinary tract infections. If the patient is known to have recurring infections of the urinary tract, he/she may be given antibiotics to prevent further infections. Patients with vesicoureteral reflux (see earlier section) are often treated with antibiotics, follow-up ultrasounds, and follow-up cystourethograms (see here).

If the kidney is severely damaged, it may need to be removed. Removal of the kidney is known as a nephrectomy. If a kidney needs to be removed, the other kidney takes over for the functioning of the removed kidney. Some doctors recommend removing a kidney with many cysts on it because it does not work. Other doctors do not recommend removing a kidney with many cysts on it unless its large size causes problems or if there is something present that is blocking the urine.

For some unborn children with severe hydronephrosis, some hospitals are experimenting with surgeries to decrease blockages or pressure in the unborn child when it is still in the uterus. The uterus is a hollow organ in a female's body where the egg is implanted and the baby develops. This type of surgery is usually only done when the kidneys are very abnormal and their lungs are usually not well developed.


Hydronephrosis is also known as pelvocaliectasis and pyeloureterectasis.