Ureteropelvic junction (UPJ) obstruction is a condition in which a blockage occurs in part of the urinary system. Urine is formed in the kidneys, waste- filtering organs located in the mid-back, just below the rib cage.
The renal pelvis is the part of the kidney where urine is stored after it is produced. From the kidneys, urine flows down the ureters, two thin tubes that connect the kidneys to the bladder.
The ureteropelvic junction is the area where the ureter attaches to the renal pelvis of the kidney. When a blockage occurs at the junction, it can decrease the flow of urine down the ureter and cause increased fluid pressure inside the kidney. This increased pressure can impair kidney function over time.
The most common cause of UPJ obstruction is congenital: a person is born with obstruction and develops symptoms over time. Other causes include injury to the area, stone disease, infection, and age-related changes in body shape. Symptoms of UPJ obstruction ma y include intermittent side or back pain and, when infection is involved, high fever.