This is a condition in which the urine collecting system of the kidney becomes stretched and distended because of an obstruction to the free outflow of urine from the kidney down the urine tube (ureter) to the bladder. As a result, secondary changes can occur in the kidney. The obstruction may be at any level, but is most common at the point at which the wide collecting system (the pelvis) of the kidney joins the narrow ureter.

Symptoms

There is pain in the back (loin), sometimes made worse by drinking. Secondary infection is common, causing fever, painful urination and often blood in the urine. Occasionally the condition is silent until late symptoms arise.

Causes

Obstruction at the outlet of the bladder will cause hydronephrosis of both kidneys, because in this case the back pressure is applied equally to both. Obstruction may be from a urinary stone, a tumour, a blood clot, inflammatory narrowing or external pressure from any cause, including an abnormally placed artery to the kidney. One of the most common causes is enlargement of the prostate gland. Hydronephrosis can even be caused by a very tight foreskin (phimosis). Obstruction in one ureter, as from a stone, will affect only the kidney on that side.

Treatment

Treatment involves the identification and removal of the cause of the obstruction. However, as an emergency measure, temporary drainage of the affected kidney through a fine tube (catheter) may save it. If one kidney only is affected and is severely damaged, it will usually be removed to prevent other serious complications.