Hydronephrosis is a condition in which one or both of your kidneys become stretched and swollen. This is usually because:
- there is a blockage somewhere in your urinary system (along the urine flow path), which is the usual cause, or
- urine is flowing from the bladder back to the kidneys
It can sometimes cause a pain in your side, or there may be no symptoms at all (see Symptoms).
Why does hydronephrosis develop?
A blockage in the urinary system can be caused by a variety of things, such as a kidney stone, a growth or tumour or a kink in the ureter (see Causes for more information).
If hydronephrosis is caused by urine back-flow, it is because the one-way valve in your bladder that normally prevents this is damaged or obstructed.
Where can the blockage occur?
Urine flows from the kidneys to the bladder via narrow tubes called the ureters, and the blockage can be at any point along this path. It often occurs where the renal pelvis (the wide urine-collecting system in each kidney) joins the narrow ureter.
This blockage causes a build-up of urine inside the kidney, putting pressure on the kidney.
Who is affected by hydronephrosis?
Hydronephrosis can occur in people of any age. It is increasingly being diagnosed in unborn babies, where the baby's swollen kidney is detected by using a routine ultrasound test that is given to all pregnant women.
How common is it?
About one in every 300 people has one kidney affected by hydronephrosis (unilateral hydronephrosis), and about one in every 600 has both kidneys affected (bilateral hydronephrosis).
How serious is it?
Most people make a full recovery when hydronephrosis is detected and treated early (see Treatment). More than eight out of 10 babies with hydronephrosis have no serious problem.
If hydronephrosis is left undiagnosed or is not treated quickly enough, it can cause kidney damage or kidney failure.
If you already have hydronephrosis, call your doctor if you have symptoms of urine infection (burning when you pass urine or passing urine frequently, with fever, chills or pain in your side or back).
