Hydronephrosis

Hydronephrosis is distention (dilation) of the kidney with urine, caused by backward pressure on the kidney when the flow of urine is obstructed.

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  Kidney stones are common causes of urinary tract obstruction.
  
  
  
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  When hydronephrosis occurs quickly, people may have excruciating pain, most often in the flank (the area between the ribs and the hips).
  
  
  
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  When hydronephrosis occurs more gradually, people may have no symptoms or experience attacks of dull, aching discomfort in the flank.
  
  
  
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  Doctors initially use bladder catheterization (or ultrasonography) to detect hydronephrosis, and they may use ultrasonography or another imaging test to determine the site of the blockage.
  
  
  
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  Treatment depends on the cause of the obstruction.
  
  
  

Normally, urine flows out of the kidneys at extremely low pressure. If the flow of urine is obstructed, urine backs up behind the point of blockage, eventually reaching the small tubes of the kidney and its collecting area (renal pelvis), distending the kidney and increasing the pressure on its internal structures. The elevated pressure from obstruction may ultimately damage the kidney and can result in loss of its function. When the flow of urine is obstructed, urinary tract infections are fairly common and stones are more likely to form. If both kidneys are obstructed, kidney failure may result.

Long-standing distention of the renal pelvis and ureter can also inhibit the rhythmic muscular contractions that normally move urine down the ureter from the kidney to the bladder (peristalsis). Scar tissue may then replace the normal muscular tissue in the walls of the ureter, resulting in permanent damage.