Hydronephrosis

Hydronephrosis is the swelling/enlargement of a kidney due to the backup of urine.

It happens when urine cannot drain out from the kidney to the ureters down to the bladder due to a blockage or obstruction.

Hydronephrosis can occur in one or both kidneys.

Hydronephrosis is not a disease itself but occurs when there is either an obstruction of the outflow of urine, or reverse flow of urine already in the bladder (called vesicoureteral reflux).

It is a manifestation of a present or previous underlying cause.