Hydronephrosis 

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 (see hydronephrosis – symptoms). 

Causes of hydronephrosis

There are two main causes of hydronephrosis. It can occur when one of the following happens:

• There is a blockage somewhere in your urinary tract (see box, left), 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).

Hydronephrosis can occur in pregnant women and in cases where cancers develop inside the urinary tract, such as 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. Kidney stones are also a common cause of hydronephrosis in both men and women.

See hydronephrosis – causes for more information on this.

For most cases of hydronephrosis, surgery is required to drain urine away from the kidneys and remove any blockage. See hydronephrosis – treatment for more information on this.

Antenatal hydronephrosis

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

The most common cause of antenatal hydronephrosis is thought to be underdevelopment of the urinary tract, which leads to urine becoming trapped inside a kidney.

As a parent, it can initially 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 occurring, as bacteria can breed in the trapped urine. In some cases, surgery may be needed.

See hydronephrosis – treatment for more information.

How common is hydronephrosis?

In England, it is estimated each year that around 1 in every 300 people has one kidney that is affected by hydronephrosis (unilateral hydronephrosis), while 1 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 1 in every 100 pregnancies is affected by antenatal hydronephrosis.

Outlook

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 kidney failure (loss of normal kidney function).