Cyst in kidney

  My 17 yr old son had the right kidney removed 4 yrs ago. It had been damaged due to a blockage, they're not sure when. At the post surgical check up they found a cyst in the left one. In the 4 years it has shrunk from 1.5 cm to 1.3 cm. It is in an usual spot though. It is in the centre of the kidney not out closer to the wall. Could it move and cause a blockage? Is it common or something to worry about? Of course I'm worrying.
--------------------------------------------------------------------------
Dear Debbie,
A cyst in the kidney is something that needs to be followed with periodic radiologic studies and renal function studies, most likely ultrasound and creatinine.  A cyst is almost always in the parenchyma and rarely would be a source of obstruction.  They may increase or decrease in size however they don