does upj cause hydronephrosis?
In some children, the root cause of the hydronephrosis may never be known. While there can be many conditions that lead to hydronephrosis, the most common causes are obstructions (blockages) that reduce the ability of urine to flow out of the kidney and into the bladder. UPJ obstruction is a blockage at the point where the kidney meets the ureter (the tube that carries urine to the bladder).