Hydronephrosis is a condition that puts pressure on the kidneys and can lead to damage. Often, something inside or outside of the urinary tract blocks the urine flow out of the kidneys and causes hydronephrosis.

Hydronephrosis is a condition affecting one or both of the kidneys. When a person’s urine cannot drain out of a kidney properly, the organ can swell up or stretch.

Blockages in the urinary tract that can lead to hydronephrosis include kidney stones or an enlarged prostate. Often there is a problem with the muscle near where the urethra and bladder connect. This makes urine back up into the kidneys.

In this article, we examine hydronephrosis, its main symptoms, and its causes. We also cover diagnosis, treatment, and complications.

Share on Pinterest
PhotoAlto/Frederic Cirou/Getty Images

The urinary system consists of the bladder, kidneys, and the tubes that link the kidneys to the bladder, known as ureters.

When working correctly, the kidneys filter blood to remove waste products from the body. The kidneys create urine, which carries the waste products down each linking tube to the bladder. Urine then passes through a tube called the urethra when a person urinates, expelling it from their body.

Hydronephrosis can develop when there is a problem with the function of the urinary system. It can happen to a person of any age. It usually affects only one kidney. More rarely it can impact both.

In adults, hydronephrosis may not cause any symptoms, depending on the cause. When symptoms do occur, they may include:

  • Less frequent or lighter urination
  • blood in the urine
  • pain in the back, abdomen, or side of the body
  • any symptoms of a urinary tract infection (UTI), such as painful urination, cloudy urine, or a strong urge to urinate
  • fever
  • nausea and vomiting

When hydronephrosis occurs in babies, they commonly have no symptoms. When they do, symptoms may include:

  • multiple UTIs, when the only sign may be an unexplained fever
  • pain in the abdomen or side
  • blood in the urine
  • fever
  • not feeding well
  • lack of energy
  • irritability

One of two main problems causes hydronephrosis.

During a vesicoureteral reflux (VUR) episode, the muscular valve where the urethra connects to the bladder does not work correctly. This forces urine to reflux, or flow backward, into the kidney.

Sometimes there is an obstruction in the bladder, kidney, or linking tubes. This also prevents urine from leaving the kidney. The underlying cause could also be a blockage, pressure, or flow issue from outside the urinary system.

In adults, many things can cause an obstruction, but it is usually due to an underlying medical condition. For example:

  • Pregnancy can cause the womb to push against and block the tubes connecting the bladder and kidneys. Hydronephrosis during pregnancy is not unusual.
  • Kidney stones can move out of the kidney into a tube in the urinary system and cause a blockage.
  • An enlarged prostate gland can wrap around the urethra between the bladder and penis, which can happen as a person ages. This can compress and obstruct the urethra near the urinary bladder outlet.
  • Certain cancers can affect the urinary system. These include kidney, prostate, bladder, cervical, and ovarian cancer. If a tumor is pressing against part of the urinary system, it can obstruct the flow of urine from the kidneys.
  • The tubes connecting the bladder and kidneys can become blocked or narrowed. This may happen because of an injury or infection.
  • Nerves around the bladder can become damaged, which can affect how well this organ works.

In babies, an obstruction may happen if a part of the urinary system develops incorrectly before birth.

Doctors typically use a hydronephrosis ultrasound scan to diagnose the condition. This type of scan uses sound waves to see the organs inside the body, allowing a doctor to see whether a person’s kidneys are swollen.

Most people will have an ultrasound scan during pregnancy to check the health of the developing fetus. This gives a picture of the fetus and the fetus’ internal organs. If the fetus’ kidneys appear swollen, the person will need to have further ultrasound tests throughout the pregnancy.

After birth, doctors can perform an ultrasound of the baby’s kidneys in the same way they would perform an ultrasound of an adult’s kidneys

If a person’s kidneys appear swollen on an ultrasound picture, the doctor may need to do more tests. These tests can help find the underlying cause of the hydronephrosis.

For example:

  • a urine test can help check for infection or blood
  • a blood test can help check for an infection
  • a specialized nuclear scan of the kidneys can help show how urine is moving through the body
  • a CT scan can give a 3D picture of the urinary system and adjacent organs

A voiding cystourethrogram is a special X-ray that shows if reflux or obstruction is present. The doctor adds a dye to the urine in the bladder. This helps show the path of urine flow on an X-ray. Doctors use this test to diagnose VUR in adults and babies.

Doctors determine treatment based on the underlying cause of a patient’s hydronephrosis and the severity of their condition and symptoms.

When hydronephrosis is severe, doctors may need to drain the backlog of urine in order to reduce the pressure on the bladder and the risk of permanent kidney injury. They do this by inserting a thin tube called a catheter through the urethra into the bladder or a special tube called a nephrostomy tube into the kidney.

Before treating the underlying cause of hydronephrosis, the doctor may prescribe something to control any pain. They can also prescribe an antibiotic to treat or prevent a urinary tract infection.

In adults, the underlying cause of hydronephrosis can sometimes just fix itself. This means a person won’t need any treatment.

More often, however, a doctor will need to do surgery to remove the obstruction or fix the reflux. This surgery can be minimally invasive, with only a few small incisions, and involve a thin tube with a light and camera. At other times, it may require larger incisions and more instruments. In some cases, doctors can also treat hydronephrosis with medication.

When pregnancy is the cause of hydronephrosis, the condition will usually go away without treatment once the person’s pregnancy comes to an end.

For a baby found to have hydronephrosis before birth, a doctor might need to do some further tests or ultrasound imaging on the baby in its first few weeks to make sure its kidneys and bladder are working normally. In many babies, hydronephrosis can resolve on its own over time.

Since babies with hydronephrosis are more likely to develop a UTI, doctors may also give them an antibiotic to reduce the risk of developing a urinary infection.

Babies with severe hydronephrosis usually need surgery. If the cause is a blockage in the tubes between the kidney and bladder, doctors can do a surgery known as a pyeloplasty under a general anesthetic. Doctors remove the section of the tube that is blocked and connect the two remaining ends.

Untreated hydronephrosis can put a lot of pressure on a person’s kidneys. This can cause permanent kidney damage or even kidney failure. Kidney failure means that the kidneys have stopped working.

If both kidneys develop total kidney failure, a person will need a kidney transplant or dialysis. The latter is a process that filters waste and extra fluid from the blood using a machine outside the body.

Hydronephrosis prevents a person’s urine from draining properly out of the kidneys. The treatment usually depends on the underlying cause of the condition.

If caught and treated early, hydronephrosis will not usually cause any lasting medical problems. In babies, if doctors don’t discover hydronephrosis in an ultrasound before birth, the condition can be harder to diagnose after birth. People should watch for signs of a UTI in babies to help spot a possible problem.

Early medical advice and treatment can help to ensure a quicker recovery for both babies and adults.