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.

Read more about the symptoms of hydronephrosis.

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

Read more about the causes of hydronephrosis.

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.

Read more about how hydronephrosis is 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).

Read more about complications of hydronephrosis.

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.

Read more about treating antenatal hydronephrosis.

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.

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