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.

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.

There may not be any symptoms. When symptoms occur, they may include:

• Back or flank pain
• Bloody urine (hematuria)
• Lump in the abdomen (abdominal mass)
• Kidney infection
• Poor growth in infants (failure to thrive)
• Urinary tract infection, usually with fever
• Vomiting

An ultrasound during pregnancy may show kidney problems in the unborn baby.

Tests after birth may include:

• BUN
• Creatinine clearance
• CT scan
• Electrolytes
• IVP
• Nuclear scan of kidneys
• Voiding cystourethrogram

Surgery to correct the blockage allows urine to flow normally. Open (invasive) surgery is usually performed in infants. Adults may be treated with less-invasive procedures. These procedures involve much smaller surgical cuts than open surgery, and may include:

• Endoscopic (retrograde) technique does not require a surgical cut on the skin. Instead, a small instrument is placed into the urethra and allows the surgeon to open the blockage from the inside.
• Percutaneous (antegrade) technique involves a small surgical cut on the side of the body between the ribs and the hip.
• Pyeloplasty removes scar tissue from the blocked area and connects the healthy part of the kidney to the healthy ureter.

Recently, laparoscopy has been used to treat UPJ obstruction in children and adults who have not had success with other procedures.

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.

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.

In severe cases, rapidly taking pressure off the kidney (kidney decompression) immediately following birth may greatly improve kidney function.

Permanent loss of kidney function (kidney failure) is a possible complication of untreated UPJ obstruction. Even after treatment, the affected kidney may be at increased risk for infection or kidney stones.

Call your health care provider if your infant has bloody urine, fever, a lump in the abdomen or if the baby seems to have back pain or pain in the flanks (the area towards the sides of the body between the ribs and the pelvis).

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.