Hydronephrosis

Hydronephrosis is a condition in which one or both of your kidneys become stretched, or swollen, due to a build-up of pressure when urine can't drain out of your kidney.

This build-up of urine is usually caused by a blockage in the normal flow of urine out of your kidneys, down the urine tubes (ureters), to your bladder. The blockage can be at any point of this flow from kidney to bladder, but is most common where the wide urine-collecting system of each kidney (the renal pelvis) joins the narrow tube of the ureter.

Occasionally, hydronephrosis can be caused by urine flowing back from your bladder to your kidneys. This can happen if the valve in your bladder that normally prevents this 'backwash' is damaged or obstructed.

Hydronephrosis can occur in people of any age, including unborn babies, where it will be detected by the routine ultrasound test given to all pregnant women.

About 1 in every 300 people has one kidney affected by hydronephrosis, and about 1 in every 600 has both kidneys affected.

Hydronephrosis usually develops over just a few hours when a blockage forms quickly - from a kidney stone for example. But it can develop gradually over a period of weeks or months if the blockage is due to something like a slow-growing tumour.

The severity of your symptoms will depend on the extent of the blockage and the amount your kidney is stretched. The type of symptoms you experience will depend on the location of the blockage and the length of time the flow of urine remains blocked.

When the blockage begins quickly (acute hydronephrosis), you will usually experience a severe pain (renal colic) in your back or side between your ribs and hip. The pain will be on the side of the affected kidney, or if both kidneys are affected, on both sides.

Other symptoms can include:

• swelling in your abdomen,
• nausea,
• vomiting,
• fever,
• needing to go to the toilet more often than normal, and
• pain when you pass urine.

A partial blockage of the normal urine flow may reduce the rate you are able to urinate when you go to the toilet. If both the ureters from your kidneys, or your urethra, are blocked, you may be completely unable to urinate.

Hydronephrosis caused by a slow-developing blockage may have the same symptoms as acute hydronephrosis, no symptoms at all, or a dull, aching pain in your side that comes and goes.

If only one of your ureters or kidneys becomes blocked then you will experience unilateral hydronephrosis - affecting only one kidney. This commonly results from a blockage at the point where the wide urine-collecting system of each kidney (the renal pelvis) joins the narrow tube of the ureter.

Causes of this type of blockage include:

• your kidney developing incorrectly so that the ureter joins the kidney at too high a point,
• a kink forming at the point where the ureter meets the kidney because one of your kidneys has shifted downwards,
• a kidney stone,
• the ureter being squeezed by an artery or vein that is in an abnormal position, and
• a tumour in your kidney.

Unilateral hydronephrosis can also result from a blockage in one of your ureters.

Causes of this type of blockage include:

• a stone in the ureter,
• a tumour in the ureter, or near the ureter and putting pressure onto it,
• a narrowing of the ureter resulting from an injury, infection, surgery, or birth defect, and
• a disorder of the nerves or muscles in the ureter.

If the urine flow is blocked at your bladder then the blocked urine will apply pressure to both kidneys equally. In this case you can suffer bilateral hydronephrosis - affecting both kidneys.

Causes of this type of hydronephrosis include:

• a urinary stone,
• a blood clot,
• a tumour in the bladder
• your bladder becoming inflamed or pressed upon by something else within your abdomen,
• a disorder of the nerves or muscles in the bladder,
• bulging of the lower end of the ureter into the bladder (ureterocele),
• cancer of the bladder, prostate or other organs in the pelvis, and
• enlargement of the prostate gland.

Hydronephrosis of both kidneys can occur during pregnancy if the uterus enlarges so that it squeezes the ureters. This form of hydronephrosis usually resolves when the pregnancy ends.

Hydronephrosis is initially diagnosed from your symptoms and a physical examination to check for swelling in your side or abdomen caused by a swollen kidney. Your doctor will then need to perform tests to confirm their diagnosis. These tests are also used to detect hydronephrosis that is suspected but does not have any symptoms.

The tests may include:

• a CT scan (computerised tomography scan),
• an MRI scan,
• an ultrasound scan,
• intravenous urography - a procedure where your kidneys are X-rayed after a dye that can be seen on X-rays has been injected into your bloodstream. The test provides information about the flow of urine through your kidneys,
• an endoscopy - a procedure where a flexible viewing tube is inserted into your urethra to look at possible sites of blockage, and
• a urine test.

Early diagnosis of hydronephrosis is important as most blockages causing the condition can be corrected. A delay in treatment can lead to permanent kidney damage.

Treatment of hydronephrosis depends on the cause and severity of the blockage to normal urine flow. The aim of treatment is to remove the build-up of urine, relieve the pressure on your kidney, and prevent permanent kidney damage.

In acute hydronephrosis, the build-up of urine within your kidney must be drained urgently so that the kidney is not damaged. A catheter may be inserted into your bladder or a tube inserted directly into your kidney through a small incision in your skin. This allows urine to flow and the pressure on the kidney to be relieved.

Hydronephrosis that develops slowly does not usually require urgent treatment, but once again the urine that has built up above the blockage must be drained. Soft tubes may be inserted into the ureter to bypass the blockage and allow urine to flow.

Once the pressure on your kidney has been relieved, the cause of the build-up of urine must be treated. This usually means the removal of a blockage. The removal method depends on the exact cause, but most blockages require some sort of surgery. For example, surgery may be needed to remove a stone from your kidney or ureter, or to remove a narrow or abnormal part of a ureter. If the junction of the ureter and the bladder is blocked, the ureter may need to be attached to a different part of your bladder.

If hydronephrosis is diagnosed in your baby, during pregnancy, your baby will be monitored with ultrasound scans to check that he or she is growing normally and that their kidneys are not getting too large. If the hydronephrosis is causing problems for your baby the fluid may need to be drawn off while the baby is in your womb. However, this is very uncommon. After your baby is born the hydronephrosis will be monitored with ultrasound scans and the other standard tests for hydronephrosis. Treatment will then depend on the cause.

Most people make a full recovery when hydronephrosis is detected and treated early on.

Hydronephrosis often causes kidney infection (pyelonephritis) and urinary tract infection. The symptoms of kidney infection include all those listed for hydronephrosis, as well as pus in your urine and pain in the area around your bladder.

If hydronephrosis is not diagnosed or treated promptly it can damage a kidney severely or cause kidney failure. If this happens and your second kidney is functioning properly, the damaged kidney will usually be removed.