Hydronephrosis is a condition where one or both kidneys become stretched and swollen as a result of a build-up of urine inside the kidney(s).

The most common symptom of hydronephrosis is a severe pain that develops in your back or side, between your ribs and hip.

Causes of hydronephrosis

There are two common causes of hydronephrosis. It can occur when:

there is a blockage somewhere in your urinary tract, which is the most common cause

something disrupts the normal workings of your bladder which causes urine to flow back from the bladder and into the kidney(s)

Kidney stones are a common cause of hydronephrosis in both men and women.

Hydronephrosis can occur in pregnant women and in cases where cancers develop inside the urinary tract, such as bladder cancer, or in the cervix (cervical cancer). The cervix is the neck of the womb.

In men, hydronephrosis can sometimes occur in those who have a swollen prostate gland or prostate cancer. 

Treating hydronephrosis

For most cases of hydronephrosis, surgery is required to drain urine away from the kidneys and remove any blockage. The underlying cause will then need to be treated.

The outlook for hydronephrosis is generally good as long as the condition is diagnosed and treated promptly. If left untreated for several weeks, the kidney(s) may become scarred, which could lead to loss of normal kidney function (kidney failure).

Antenatal hydronephrosis

Hydronephrosis is increasingly being found in unborn babies during routine ultrasound scans carried out in pregnancy. This type of hydronephrosis is known as antenatal hydronephrosis.

As a parent, it can be worrying to learn that your baby has a problem with their kidneys. However, most cases of antenatal hydronephrosis are not serious and should not affect the outcome of your pregnancy.

About four out of five cases of antenatal hydronephrosis will resolve on their own before, or shortly after, birth. The remaining cases may require treatment with antibiotics to prevent kidney infections, as bacteria can breed in the trapped urine. In some cases, surgery may be needed.

How common is hydronephrosis?

In England, it is estimated each year that around one in every 300 people has one kidney affected by hydronephrosis (unilateral hydronephrosis), while one in every 600 people have both affected (bilateral hydronephrosis).

Antenatal hydronephrosis is one of the most common abnormalities detected during antenatal scanning. It is estimated that about one in every 100 pregnancies is affected by antenatal hydronephrosis.

Symptoms of hydronephrosis 

The symptoms of hydronephrosis will depend on whether the urine blockage occurred quickly (acute hydronephrosis) or gradually (chronic hydronephrosis).

If the blockage forms quickly – for example, as a result of a kidney stone, your symptoms will develop over the course of a few hours. If the blockage develops gradually, over a period of weeks or months, you may experience few or no symptoms.

Your symptoms can also be more severe depending on where the problem is, the length of time that the flow of urine remains blocked and how much your kidney has been stretched.

Acute hydronephrosis

The most common symptom of acute hydronephrosis is a severe pain in your back or side, between your ribs and hip. The pain will be on the side of the affected kidney or on both sides if both kidneys are affected. In some cases, the pain may travel towards the testicles (in men) or vagina (in women).

The pain usually comes and goes and is often worse when drinking fluid. As well as pain, you may also experience nausea and vomiting.

If the urine inside your kidney becomes infected, you will also have symptoms of a kidney infection, such as:

a high temperature (fever) of 38oC (100.4oF) or above

uncontrollable shivering

If the blockage of urine has been caused by a kidney stone, you may notice the presence of blood in your urine. In severe cases of hydronephrosis, one or both of your kidneys may be noticeably swollen to the touch.

Chronic hydronephrosis

If your hydronephrosis is caused by a blockage that develops over a long period of time, you may experience:

the same symptoms as acute hydronephrosis (see above)

no symptoms at all

a dull ache in your side that comes and goes

You might also urinate less often than you used to.

When to seek medical advice

Always contact your GP if you:

develop a severe and persistent pain

have symptoms, such as a high temperature, which suggest that you may have an infection

notice a uncharacteristic change in how often you urinate

Causes of hydronephrosis 

Hydronephrosis is most often caused by a blockage inside the urinary tract or something disrupting the normal workings of the urinary tract.

Common causes

Kidney stones are a common cause of hydronephrosis in both men and women. Kidney stones are small stones that form in the kidneys. They can sometimes travel out of a kidney and into the ureters where they can block the flow of urine.

Causes in men

In men, the two most common causes of hydronephrosis are:

non-cancerous swelling of the prostate gland (benign prostatic hyperplasia)

prostate cancer

Both conditions can place pressure on the ureters, which can block the flow of urine. The ureters are the tubes that run from your kidneys to your bladder.

Causes in women

In women, common causes of hydronephrosis include:

pregnancy – during pregnancy the enlarged womb (uterus) can sometimes place pressure on the ureters

cancers that develop inside the urinary tract, such as bladder cancer or kidney cancer

cancers that develop inside the reproductive system, such ascervical cancer, ovarian cancer or cancer of the womb

Abnormal tissue growth associated with cancer can place pressure on the ureter or disrupt the workings of the bladder.

Other causes

Other less common causes of hydronephrosis include:

a blood clot (embolism) – which develops inside the urinary tract

endometriosis – a condition where tissue that should only grow inside the womb starts to grow outside of the womb; this abnormal growth can sometimes disrupt the urinary tract

tuberculosis – a bacterial infection that usually develops inside the lungs but in some cases can also spread to the bladder

damage to the nerves that control the bladder (neurogenic bladder)

ovarian cysts – fluid-filled sacs that develop inside the ovaries; larger ovaries can sometimes place the bladder or ureter under pressure

narrowing of the ureter as a result of injury, infection or surgery

Antenatal hydronephrosis

Causes of antenatal hydronephrosis include:

a blockage – at the point where the ureters join the kidneys, although in many cases there is no obvious cause

primary vesicoureteral reflux – this is a childhood condition where the valve that controls the flow of urine between the bladder and the ureter does not function properly, allowing urine to flow back up to the kidneys; most children will grow out of primary vesicoureteral reflux

Diagnosing hydronephrosis 

Hydronephrosis is usually diagnosed using an ultrasound scan. Further tests may be needed to find out the cause of the condition.

An ultrasound scan uses sound waves to create a picture of the inside of your kidneys. If your kidneys are swollen, this should show up clearly.

Further tests

You may need a number of additional tests to help determine the cause of hydronephrosis. These may include:

blood tests – which can be used to check for infection

urine tests – which can be used to check for infection as well as traces of blood (if blood is found it could be caused by a kidney stone)

intravenous urography – this is an X-ray of your kidneys that is taken after a special dye has been injected into your bloodstream; the dye highlights the flow of urine through your urinary tract, which can be useful for identifying any blockages

computerised tomography (CT) scan – this is similar to an X-ray but uses multiple images and a computer to build up a three-dimensional picture of the inside of your body

Antenatal hydronephrosis

Hydronephrosis may be diagnosed in your baby during pregnancy, during a routine ultrasound scan.

Your baby will be monitored with ultrasound scans to check it is growing normally and the kidneys are not getting too large.

Treating hydronephrosis 

If you have hydronephrosis, your treatment will depend on what is causing the condition and how severe the urinary blockage is.

The aim of treatment is to:

remove the build-up of urine and relieve the pressure on your kidney(s)

prevent permanent kidney damage

treat the underlying cause of hydronephrosis

Most cases of hydronephrosis will need to be treated surgically using a combination of techniques (see below).

The timing of your treatment will depend on whether you have an infection, because there is a risk that an infection could spread into your blood. This is known as blood poisoning or sepsis and it can be very serious. In these circumstances, it may be recommended that surgery is carried out on the same day that the diagnosis is confirmed.

Immediate surgery may also be recommended if both of your kidneys are affected or if you have symptoms including severe pain, vomiting and nausea that can't be relieved with medication.

If you do not have these symptoms, it may be considered safe to delay surgery for a few days.

Draining the urine

The first stage in treating hydronephrosis is to drain the urine out of your kidneys. This will help to ease your pain and prevent damage to your kidneys.

A thin tube called a catheter may be inserted into your bladder through your urethra (the tube through which urine is passed out of the body), or directly into your kidney through a small incision in your skin. This will allow urine to flow and relieve the pressure on the kidney.

Treating the underlying cause

Once the pressure on your kidney has been relieved, the cause of the build-up of urine must be treated. This will usually involve removing a blockage.

Blockages of the ureter (a common cause of hydronephrosis) can be treated using a type of surgery called ureteral stenting. It involves placing a small tube inside the ureter which is used to bypass the site of a blockage. The stent can be passed into the ureter (the tube that passes from the kidney to the bladder) without making major incisions in your body.

Once the urine has been drained and the ureter unblocked, the underlying cause will need to be treated to prevent hydronephrosis returning.

Some possible causes and their treatments are described below.

Kidney stones – these can be broken up using sound waves or lasers (Read more about treating kidney stones).

A swollen prostate – this can be treated with medication or, less commonly, surgery to remove some or all of the prostate (Read more about treating prostate enlargement).

Cancers – some cancers, such as cervical cancer or prostate cancer, are associated with hydronephrosis and can be treated using a combination of chemotherapy, radiotherapy and surgery to remove the diseased tissue.

If a woman's pregnancy is causing hydronephrosis, there is little that can be done to cure it other than waiting for the pregnancy to take its natural course. However, the condition can be managed by regularly draining the kidneys with a catheter throughout the pregnancy to prevent kidney damage.

Antenatal hydronephrosis

Most cases of antenatal hydronephrosis do not need treatment because they usually resolve on their own before birth. However, frequent ultrasound scans will probably be recommended to check the kidneys.

If hydronephrosis is present after birth, treatment will depend on the underlying cause. If it's caused by primary vesicoureteral reflux (where the valve in their bladder does not work properly) then it's unlikey to need treatment. This is because most children grow out of primary vesicoureteral reflux as they get older.

However, the urine inside their kidneys can make them more vulnerable to infection, so regular doses of antibiotic tablets may be recommended as a precaution.

Your child will need regular urine tests and ultrasound scans to monitor how they are responding to antibiotic treatment and to assess the swelling inside their kidney(s).

Surgery will be considered if your child does not grow out of primary vesicoureteral reflux, or if they get repeated infections, even if taking antibiotics.

During surgery a substance is injected around the malfunctioning bladder valve, which should help to stop the reflux.

If your child’s hydronephrosis is caused by a blockage, this will need to be treated surgically in the same way as it is in adults (see above).

Complications of hydronephrosis 

In cases of severe hydronephrosis that are not treated promptly, scarring of the kidney can occur.

In the most serious of cases, this can lead to loss of normal kidney function (kidney failure).

Most people can function normally with just one working kidney, so the failure of a single kidney will probably not significantly affect your health or lifestyle. However, if the failed kidney has been affected by an underlying condition, such as cancer or infection, surgically removing the kidney may be recommended.

If both kidneys fail, it will have a major impact on your health. Your kidneys perform a number of important functions, such as filtering waste products from your blood and helping to regulate blood pressure. Therefore, kidney failure can cause a wide range of symptoms, such as:


swollen ankles, feet or hands (due to water retention)

shortness of breath

feeling sick

blood in your urine

There are two main treatment options for kidney failure. They are:

kidney transplant – where a donated kidney that is usually provided by a living donor is surgically transplanted into your body

dialysis – where a machine is used to replicate the most important function of the kidneys, which is filtering your blood