What Is Hydronephrosis?

Medically Reviewed by Poonam Sachdev on February 28, 2024
Written by Deanna Altomara
8 min read

Hydronephrosis is when your kidneys swell because your body can't release all of its pee. It may affect one or both kidneys, and it can occur in people of all ages. About 1 in 100 adults get hydronephrosis at some point. It also affects about 1 in 100 fetuses, but it often gets better before the baby is born.

You might also hear it called upper urinary tract dilation.

Urinary tract

Your urinary tract removes extra fluid, toxins, and waste from your body through pee. Your urinary tract is made of your kidneys, bladder, ureters, and urethra. After your kidneys filter your blood, urine passes from your kidneys to the bladder through the ureters, which are the tubes that connect your kidneys to your bladder. Any problems along the urinary tract can lead to hydronephrosis.

The urinary tract is made up of:

  • Kidneys. These filter waste from your blood. The waste is combined with extra fluid to make pee.
  • Ureters. These two tubes carry pee from your kidneys to your bladder.
  • Bladder. This sac stores pee until you’re ready to go.
  • Urethra. Pee exits your body through this tube.

Problems at any point along the urinary tract can lead to hydronephrosis.

There are two main causes of hydronephrosis: vesicoureteral reflux and urinary tract obstruction.

  • Vesicoureteral reflux. This happens when the flap between the ureter and the bladder doesn’t close properly. As a result, urine flows backward from the bladder to the kidney.
  • Obstruction in the bladder, kidney, or linking tubes. This is when a blockage forms in the urinary tract. It can be caused by many different things. For example, a ureter might swell and block the flow of pee into the bladder, or a kidney stone might block the urethra.‌

In children, over half of hydronephrosis cases have unknown causes, and the condition clears up on its own.

Adult hydronephrosis

Several conditions can cause hydronephrosis, such as:

  • Kidney stones.These are hard lumps of calcium and oxalate that can build up in your kidneys. They can become stuck in the kidneys or other parts of the urinary tract.
  • Ureteral obstruction. This is when something (like a blood clot or an enlarged prostate) presses against your ureters.
  • Nerve or muscle problems. Certain conditions can affect your urinary tract’s ability to function. For example, any damage to the nerves that control your bladder can impact your ability to pee.
  • Tumors. Tumors growing in or near your urinary tract can press against the organs and cause blockages.
  • Vesicoureteral reflux. This condition causes pee to flow the wrong way, from your bladder to your kidneys.
  • Benign prostatic hypertrophy (BPH). An enlargement of the prostate can put pressure on the urethra.
  • Narrowing of the ureters. This can happen because of injury, infections, surgery, or birth defects.
  • Ureterocele. This is when a bulge in your ureter presses against your bladder.
  • Urinary retention. This is when you can’t fully empty your bladder.

People with uteruses

If you have a uterus, other things can also cause hydronephrosis. These include:

  • Pregnancy. During pregnancy, your uterus expands and can press against one or both ureters, limiting the flow of pee from your kidneys.
  • Uterine prolapse. Also known as “fallen uterus,” this is when your uterus moves out of its usual position. 
  • Cystocele. Also known as “fallen bladder,” this is when the wall between your vagina and bladder weakens, letting your bladder push against your vagina.

Antenatal hydronephrosis

About 1 in 100 fetuses get hydronephrosis before they are born. This is called antenatal hydronephrosis, as antenatal means “before birth.” If you’re pregnant, your doctor might notice it when you get your 20-week ultrasound.

Possible causes include:

  • Narrowing of the urinary tract. This is a normal part of early development, but it can cause hydronephrosis in some fetuses.
  • Ureteral obstruction. Like adults, fetuses can have a blockage in the tubes that carry pee from the kidneys to the bladder.
  • Urethral obstruction. Sometimes, male fetuses have a blockage in their urethra.
  • Vesicoureteral reflux. For fetuses with this condition, some pee might flow backward from the bladder to the kidneys.
  • Certain birth defects. Some birth defects can lead to blockages in the urinary tract. For example, a fetus might have an extra ureter or a ureter that doesn’t enter the bladder in the right spot.
  • Multicystic kidney. This happens when a ureter is completely blocked, preventing the associated kidney from making pee. The affected kidney develops abnormally and fails to work. Luckily, the other kidney can handle the extra work without any issues.
  • Additional pee. As the fetus develops, it makes more pee, which drains into and becomes part of the amniotic fluid. Some people think that the additional pee could trigger hydronephrosis.

You may not feel any symptoms of hydronephrosis ⁠— many patients don’t. But some people may notice:

  • Nausea
  • Vomiting
  • Painful or frequent urination
  • Intense or sudden pain in your back or side, especially after drinking fluid
  • Blood in your urine
  • A general feeling of weakness or fatigue
  • Fever
  • Peeing less than usual
  • Feeling like you can’t fully empty your bladder

These symptoms depend on what’s causing your hydronephrosis and can range from mild to severe.

Sometimes, hydronephrosis can lead to a urinary tract infection (UTI). This is because pee stays in your body longer than it should, and bacteria can start to grow.

UTI symptoms include:

  • Fever
  • Chills
  • Fatigue
  • Burning or pain when you pee
  • Cloudy pee

Babies born with antenatal hydronephrosis usually don’t have any symptoms. But if they have a severe blockage, you might notice some swelling in their abdomen. Some babies might develop a UTI, which could cause symptoms such as fever, irritability, and difficulty feeding.

If you’re showing signs of hydronephrosis, it’s important to talk to your doctor. Getting diagnosed and treated can help prevent the condition from getting worse or leading to complications such as kidney damage. 

To make the diagnosis, your doctor might suggest:

  • A physical examination. First, your doctor will ask about your symptoms and medical history. Then, they’ll feel your abdomen to look for swelling or tenderness. They might also perform a rectal exam (for people with a penis) to look for signs of an enlarged prostate or pelvic exam (for people with a uterus) to examine the reproductive organs. Rectal and pelvic exams are when a doctor gently puts a gloved finger inside your body to feel for abnormalities.
  • Urine tests. This is when you pee in a cup, or a doctor collects your pee with a catheter. They then check your pee for blood, crystals, and germs.
  • Blood tests. Your doctor might check your creatinine, estimated glomerular filtration rate (a measure of how well your kidneys are working), blood urea nitrogen (BUN), and other indicators of kidney function. They might also suggest a complete blood count to check for infections.
  • Imaging procedures. Ultrasounds, MRIs, and CT scans can help doctors get a better look at what’s happening inside your body. Sometimes, the doctor might inject you with a special dye, which highlights the pee so it's easier to see in the imaging. Ultrasounds are also used for pregnant people. At 20 weeks, a doctor can perform an ultrasound to tell if your fetus has hydronephrosis.

First, your doctor might drain the extra pee from your kidneys by placing a tube called a catheter through your stomach or urethra. This will help with pain and avoid complications.

Sometimes, hydronephrosis clears up on its own. In mild cases, your doctor might recommend waiting to see if it gets better. If it doesn’t, they will treat the underlying cause.

If hydronephrosis is caused by a kidney stone, you’ll need to pass the stone (pee it out) or have it removed. Options include:

  • Shock wave lithotripsy. This is when doctors use a machine to send shock waves towards your kidney stones. The shock waves break the stones into smaller pieces so you can pee them out more easily.
  • Ureteroscopy. For this treatment, a doctor threads a tube into your urethra. Then, they break up and remove the stones stuck in your bladder or ureters.
  • Surgery. Some large stones might need to be surgically removed.

If the narrowing of a ureter is the cause, the doctor can put in a stent. This props it open, which helps the pee to flow normally.

If your hydronephrosis is caused by a tumor, scar tissue, or other major blockage, your doctor might recommend surgery.

You may be asked to stay in the hospital for observation or further testing after any procedure.

If you have a UTI or if an infection has caused your urinary tract to narrow, your doctor will treat it with antibiotics.

Treating hydronephrosis in babies

Antenatal hydronephrosis usually gets better on its own. But just in case, your doctor will probably suggest extra ultrasounds throughout your pregnancy to keep an eye on it. Usually, this condition won’t affect your pregnancy or delivery.

After the baby is born, your doctor might prescribe a low-dose antibiotic to prevent a UTI. They’ll wait a few days to give your child an ultrasound because checking too early could give a misleading result. But if your child has certain conditions (for example, both kidneys being swollen during pregnancy), they might do the ultrasound sooner.

If your baby still has hydronephrosis, your doctor might further investigate its cause. They might thread a catheter into the baby’s bladder to check for vesicoureteral reflux. This procedure is called a voiding cystourethrogram. The doctor also might do a diuretic renal scan to look for possible obstructions.

Over the next few months, the doctor will monitor your baby’s condition with regular ultrasounds and voiding cystourethrograms.

Usually, the hydronephrosis gets better on its own. In rare cases, the doctor might need to surgically remove a blockage.

Does drinking more water help with hydronephrosis?

In general, drinking plenty of water is important for kidney health, as water can help prevent and flush out kidney stones.

But drinking too much water can be dangerous, especially if you can't easily pee it out. Certain kidney problems, including hydronephrosis, can affect your ability to fully empty your bladder. In fact, one study found that quickly drinking large amounts of water might even lead to hydronephrosis. But more research needs to be done to be sure.

Ask your doctor about how much water is right for you.

The most common complication of hydronephrosis is a urinary tract infection. It’s also possible to get a kidney infection, which is a serious ⁠but treatable ⁠condition. When a chronic obstruction is finally fixed, you might experience postobstructive diuresis, a condition in which you pee more than normal.

If you notice any unusual pee symptoms, including any pain or decreased frequency, you should talk to a doctor. If you can't pee, you need immediate medical help; go to the doctor right away.

Can your kidneys recover from hydronephrosis?

With proper treatment, hydronephrosis usually doesn’t cause any long-term damage.

What is the main cause of hydronephrosis?

In adults, hydronephrosis is usually caused by a blockage in your urinary tract or backflow of pee from the bladder to the kidneys.