Hydronephrosis is a condition in which one or both kidneys begin to swell. This swelling is due to the inability of urine to drain from the kidney. Hydronephrosis is typically caused by a blockage of the ureters, the tubes through which urine drains from the kidneys. In some instances, anatomical defects can be the cause. This condition can affect patients of any age. Infants can even have hydronephrosis before birth. In some cases, there are no symptoms present whatsoever.
There are generally two causes of hydronephrosis. One is blockages where the kidney meets the ureter. These blockages can also occur when the ureter meets the bladder, but this is less common.
Vesicoureteral reflux is another potential cause, where urine backs up from the bladder to the kidney. That is a reversal of the typical flow, where urine only proceeds from the kidney to the bladder.