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 move urine to the bladder.

Ureteropelvic junction obstruction; UP junction obstruction; Obstruction of the ureteropelvic junction

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 condition can also be caused when a blood vessel is located in the wrong position over the ureter. In older children and adults, UPJ obstruction can be due to scar tissue, infection, previous treatments for a blockage, or kidney stones.

UPJ obstruction is the most frequently diagnosed cause of urinary obstruction in children. It is now commonly diagnosed during prenatal ultrasound studies. In some cases, the condition isn't seen until after birth. Children may have an abdominal mass or a urinary tract infection

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.

Pais VM, Strandhoy JW, Assimos DG. Pathophysiology of urinary tract obstruction. In: Wein AJ, ed. Campbell-Walsh Urology. 9th ed. Philadelphia, Pa: Sauders Elsevier; 2007: chap 37.

Hsu THS, Streem SB, Nakada SY. Management of upper urinary tract obstruction. In: Wein AJ, ed. Campbell-Walsh Urology. 9th ed. Philadelphia, Pa: Sauders Elsevier; 2007: chap 38.

Elder JS. Obstruction of the urinary tract. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th Ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 540.

Frokiaer J, Zeidel ML. Urinary tract obstruction. In: Brenner BM, ed. Brenner and Rector's The Kidney. 8th ed. Philadelphia, Pa ; Saunders Elsevier; 2007: chap 35.