Ureteropelvic junction obstruction is a narrowing of the ureter where it exits the kidney.

This condition can be diagnosed prenatally or postnatally. Although a ureteral obstruction can cause permanent damage to the kidney if left untreated, it is not difficult to detect and can generally be successfully treated.

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Anatomy of Ureteropelvic Junction Obstruction

This term can be better understood if it is broken down a bit. “Uretero” refers to the ureter. This is the tube that carries urine from the kidney down to the bladder. There is usually one ureter for each kidney.

“Pelvic” refers to the inner curve of the kidney, which is called the renal pelvis. The point where the ureter attaches to the pelvis of the kidney is thus called the ureteropelvic junction (UPJ).

Significant UPJ obstruction must be treated because it can cause urine to back up into the kidney. This causes the kidney to swell with urine and potentially become damaged to the point where it can have a loss in some or even all function.

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Causes of UPJ Obstruction

When this condition is detected in the fetus, it usually has a congenital cause. The most common cause is some developmental malformation of the muscle tissue at the junction. This causes the ureter to be narrow. UPJ obstruction can also present in older children or adolescents but these cases usually involves compression of the ureter by a blood vessel that crosses over.

UPJ obstruction detected after birth is generally due to a congenital narrowing. In most cases, only one kidney is affected, but it is possible for both to be obstructed.

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Diagnosis of UPJ Obstruction

UPJ obstruction will cause the kidney to swell because the urine is unable to drain. This swelling, called hydronephrosis, can be detected on an ultrasound.

Doctors have several options for diagnosing UPJ obstructions.

  • An ultrasound is used in most cases to diagnose a possible UPJ obstruction or other kidney or bladder abnormality.
  • A nuclear scan is generally obtained to diagnose kidney function and to determine if there is a blockage to the kidney with extra fluid in the drainage system.
  • Urine tests may be used to check for possible urine infections.

Treatment of UPJ Obstruction

Hydronephrosis generally corrects itself as the baby grows; a doctor will monitor mild cases rather than treating them. If there is a blockage in the UPJ, surgery is often needed to relieve the obstruction. Occasionally, this can be done with a robotic or laparoscopic procedure that only requires small incisions.

  • If your child is young and is an infant or small child, open surgical correction is generally performed.
  • The surgery involves cutting the ureter free from the kidney, clearing the obstructed area, and reattaching it. This is called a pyeloplasty and has a success rate of more than 95%.
  • During surgery, a stent may be placed in the ureter to temporarily hold it open.