Ureteropelvic Junction Obstruction

A blockage in the kidney's renal pelvis (upper end of the ureter) is called a ureteropelvic junction (UPJ) obstruction. Blocking urine flow can damage the kidney.


What is ureteropelvic junction (UPJ) obstruction?

Ureteropelvic junction (UPJ) obstruction is a blockage in the renal pelvis of the kidney. The renal pelvis is located at the upper end of each ureter (tube that drains urine from the kidneys to the bladder). The renal pelvis, which is shaped like a funnel, collects urine.

In normal cases, each of the two kidneys has one ureter. The kidneys filter the blood of waste matter and excess water, creating urine. The urine is pooled at the UPJ, and then flows down the ureters to the bladder.

In UPJ obstruction, the flow of urine is slowed or stopped completely. This raises the risk of kidney damage. In most cases of UPJ obstruction, only one of the kidneys is affected.


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How common is ureteropelvic (UPJ) junction obstruction?

UPJ obstruction occurs in about one of every 1,500 births, and is responsible for about 80% of all swollen urine-collecting systems. Males are affected at more than double the rate of females, and the left kidney is affected about twice as often as the right.

Symptoms and Causes

What are the symptoms of ureteropelvic junction obstruction?

  • Lump in the abdomen.
  • Urinary tract infection with fever.
  • Pain in the upper abdomen or back, usually after drinking fluids. The pain is caused by the backup of urine placing pressure on the kidney and surrounding tissue. In some cases, pain may come and go because the blockage isn’t complete, allowing urine to flow at times. In other instances, blockage may occur only when the person is standing upright but not when lying down.
  • Kidney stones.
  • Blood in the urine.
  • Vomiting.
  • Poor growth in an infant.


What causes ureteropelvic junction (UPJ) obstruction?

Most UPJ obstructions are present at birth, an indication that structures of the ureter or kidney did not form correctly as the fetus was developing.

In some cases an inherited tendency to obstructions will run in a family, but usually an obstruction appears in just a single family member.

A number of different types of obstructions may be present at birth, such as:

  • The opening of the ureter is too narrow.
  • There are mistakes in the number or arrangement of small-muscle cells in the ureter. These cells are responsible for the muscular contractions that push urine from the kidney down to the bladder.
  • Unusual folds in the walls of the ureter may act as valves.
  • Twists may form along the path of the ureter.
  • The ureter connects to the renal pelvis in too high a position, creating an abnormal angle between the ureter and kidney.
  • An abnormal crossing of blood vessels can press on or distort the UPJ.

Less frequently, UPJ obstructions may form in adults as a result of kidney stones, upper urinary tract infections, surgery, an abnormally crossing blood vessel or swelling in the urinary tract.

Diagnosis and Tests

How is ureteropelvic (UPJ) junction obstruction diagnosed before and after birth?

  • An ultrasound exam before a baby is born can show a UPJ obstruction. As urine gets backed up due to blockage, the kidney swells beyond its normal size, a condition known as hydronephrosis.
  • Once the baby is born, tests that measure how well urine is being produced and drained include:
    • Blood samples and urine samples such as blood urea nitrogen (BUN) and creatinine tests provide clues on how well the kidneys are filtering the blood.
    • An intravenous pyelogram (IVP) injects a dye into the bloodstream that is then traced by X-ray as it flows through the kidney, renal pelvis and ureter.
    • A nuclear renal scan uses a radioactive substance instead of a dye, and can be traced with a special camera. This shows the functioning of the kidney and how much blockage may be present.
  • Ultrasound, computed tomography (CT) and magnetic resonance imaging (MRI) scans can show obstructions in the kidney, as well as the structure of the kidneys, ureters and bladder.


Management and Treatment

How is ureteropelvic junction obstruction treated?

In many infants with UPJ obstruction, the condition may improve on its own within the first 18 months of life. During this time, repeated ultrasounds and scans are used to monitor the condition to make sure it will not cause lasting harm.

If urine flow doesn’t improve and the obstruction remains after the first 18 months of life, surgery is usually needed to fix the problem. In infants, the surgery most often used is called open pyeloplasty. In this procedure the UPJ is removed, and the ureter is reattached to the renal pelvis but with a wider opening. The goal of the surgery is to allow urine to drain freely, eliminate symptoms and reduce the chances of infection.

Minimally invasive pyeloplasty uses a laparoscope, a long thin tube requiring just a small incision through which the surgeon or a robot operates surgical tools.

Another option is to insert a wire through the ureter to reach the site of the UPJ obstruction internally. The wire is then used to cut the obstruction and a drain is inserted for a few weeks during healing. This procedure doesn’t require any incisions and involves less discomfort than the other two options, but has a lower success rate and may have to be repeated more than once.

What can be expected after treatment for ureteropelvic junction obstruction?

Open pyeloplasty usually takes a few hours to complete and has about a 95% success rate. The patient may need to stay in the hospital for two or three days following surgery. A drainage tube may be inserted into the kidney or ureter to assist in urine flow while healing takes place.

The success rate of minimally invasive techniques is on par with open pyeloplasty, but is more technically demanding of the skills of the surgeon and is dependent on patient age and size.



How can ureteropelvic junction (UPJ) obstruction be prevented?

Researchers have not found any link between a pregnant person's diet or nutrition and the formation of UPJ obstruction in a developing fetus There does not appear to be anything one can do to prevent UPJ obstruction when it's a genetic condition.

In adults not born with UPJ obstruction, reducing the chances for later development would depend on avoiding kidney stones, urinary tract infections or trauma to the kidneys.

Medically Reviewed

Last reviewed on 10/06/2020.

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