Stretching or dilation of the urinary tract may occur because of a blockage to the flow of urine, which causes increased pressure “up stream,” and leads to urine building up above the point of blockage.
Hydronephrosis can also occur due to an abnormal connection between the ureter and bladder that allows urine to flow backward toward the kidney when the bladder contracts to empty. This condition is known as reflux.
Sometimes hydronephrosis can be caused by a blockage that has cleared and left the urinary system stretched but not under any pressure.




