Hydronephrosis Dr Rob Hicks Recurrent urine infections may raise suspicion of the condition.

In this article

What is hydronephrosis? Symptoms

Causes and risk factors Treatment and recovery

Hydronephrosis (which means 'water on the kidney') occurs when one or both kidneys swell up because something is blocking the urine flow resulting in a back pressure in the urinary system.

If hydronephrosis develops over time, it may not become apparent until damage to the kidneys has occurred and the symptoms of chronic kidney failure appear. These include tiredness, weakness, poor appetite, breathlessness, frequent or reduced passing of urine and pale, itchy skin.

Recurrent urine infections may also raise the suspicion of hydronephrosis, as such infections are more likely when the flow of urine is obstructed.

Acute hydronephrosis, when the urinary system suddenly becomes blocked for example by a kidney stone, can lead to nausea and vomiting, low back pain and severe abdominal pain.

The kidneys are responsible for filtering blood. During this process useful substances such as glucose are absorbed back into the blood, and unwanted waste products and excess water are removed. These leave the kidneys as urine, which passes through long tubes called the ureters to the bladder and then out of the body through another tube - the urethra.

When the normal flow of urine is blocked, the build-up of urine can only go so far back, to the kidney. When this happens, pressure builds up above the blockage within the tubes and urine collecting chamber in the kidney, compressing the delicate tissues from the inside and causing one or both kidneys to swell.

This is called hydronephrosis and may happen because something within the urinary tract is causing the blockage, or because something is pressing on it from outside.

Kidney stones can get stuck at any point along the route from the kidneys, through the bladder and then to the outside world. Any inflammation or scarring that causes a narrowing of a portion of the route will have the same effect. This narrowing might, for example, occur in the urethra if the urethra has been damaged by an infection or the insertion of a urinary catheter has caused a stricture to develop.

One of the most common causes of narrowing in the urinary outflow system is an enlarged prostate gland that presses on the urethra.

Structures in the abdomen but outside the urinary tract - for example, a bowel tumour - may press on the one or both of the ureters.

If an abnormality is present from birth (such as a structural abnormality), problems arise in early childhood. One of the commonest is a condition called vesicouretral reflux (VUR) which occurs when the valve between the ureter and the bladder does not work properly and urine can travel back up to the kidney. However, most medical problems with the potential to cause hydronephrosis are more common with increasing age.

About one in every 300 people have one kidney affected by hydronephrosis, and in about one in every 600 both kidneys are affected.

The aim of treating hydronephrosis is to relieve the pressure on the kidneys and prevent permanent kidney damage.

If the obstruction is between the bladder and the outside (ie somewhere in the urethra or bladder outlet), a catheter may be inserted. This is a long rubber or plastic tube that helps to bypass narrowing and enables urine to flow, relieving the pressure on the kidney.

If the obstruction is higher up, between the kidney and the bladder (ie in the ureter) then an operation is usually needed to pass a fine tube known as a ureteric stent up into the ureter from the bladder to bypass the narrowing. Occasionally a kidney is drained by using a tube passed directly through the skin into the kidney. This is called a nephrostomy tube and it drains into a urine collection bag on the skin.

Any underlying cause, such as a kidney stone, enlarged prostate, or unusual abdominal mass, also needs to be treated especially if a recurrence is to be avoided. In children with hydronephrosis, an operation may be needed to correct structural abnormalities such as VUR.

Full recovery can be expected when hydronephrosis is detected and treated early. However, if hydronephrosis goes untreated, damage to the kidney may eventually lead to kidney failure.

This article was last medically reviewed by Dr Trisha Macnair in March 2009.