When a kidney stone blocks a ureter (the tube that carries urine from the kidney to the bladder), urine backs up into the kidney.  Kidney damage and infection can occur because the urine is not able to drain normally. 

A nephrostomy is a surgical procedure where a tube is inserted through the skin into the kidney.  This tube allows the urine to drain from the kidney.  The urine will drain into a bag placed outside of the body.  This procedure is done under general anesthesia in the Interventional Radiology department.