Hello Kari.Maki, Welcome to Healthcaremagic.com As I m sure you know, ureteropelvic junction (UPJ) obstruction is a blockage in the area that connects the renal pelvis (part of the kidney) to one of the tubes (ureters) that moves urine to the bladder. UPJ obstruction generally occurs when a baby is still growing in the womb. This is called a congenital condition (present from birth). Most of the time, the blockage is caused when the connection between the ureter and the renal pelvis narrows. This causes urine to build up, damaging the kidney. The most severe cases of UPJ obstruction may require surgery early in life. However, the majority of cases may not require surgery until later in life, and some cases do not require surgery at all. Early diagnosis and treatment of UPJ obstruction may help preserve future kidney function. UPJ obstruction diagnosed before birth or early after birth may actually improve on its own. Most patients do well with no long-term consequences. Significant kidney damage may occur in those who are diagnosed later in life. Current treatment options provide good long-term outcomes. Pyeloplasty provides the greatest long-term success. A tube called a stent may be placed to drain urine from the kidney until the patient heals. A nephrostomy tube, which is placed in the patient s side to drain urine, may also be needed for a short time after the surgery. This type of tube may also used to treat severe infections before surgery. Cortical thinning indicates that there is ongoing kidney damage. Once this damage occurs, it is irreversible. The cortex of the kidney is the portion that filters the urine. Talk with your nephrologist as to the complications of having the pyeloplasty or waiting to see if your son s condition improves. Be well, Dr. Kimberly