An Overview of Ureteropelvic Junction Obstruction

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Ureteropelvic junction (UPJ) obstruction is a condition where the part of the kidney that normally drains urine becomes blocked. This blockage prevents the normal flow of urine out of the kidney and into the bladder, which can lead to kidney damage and swelling (called hydronephrosis).

UPJ obstruction is usually congenital, meaning it stems from kidney development problems in a fetus. Less commonly, UPJ obstruction is acquired.

In infants, symptoms of UPJ obstruction may include a mass in the abdomen, blood in the urine, and failure to thrive. Older children and adults may experience intermittent flank pain that worsens with caffeine consumption (or alcohol in adults) and nausea and vomiting.

Several tests are used to diagnose UPJ obstruction, including blood and urine tests and various imaging tests to visualize the urinary tract system. The treatment of UPJ obstruction requires surgery in order to relieve the obstruction; although, in many cases, especially in infants, the obstruction resolves on its own, so surgery is avoided.

Hydronephrosis or Swollen Kidney
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Ureteropelvic Junction Obstruction Symptoms

The symptoms of ureteropelvic junction obstruction depend on the age of the patient.


Since UPJ blocks normal urine flow, the affected kidney will become swollen. This kidney swelling is called hydronephrosis, and in congenital UPJ obstruction, is usually seen on a prenatal ultrasound, while the fetus is still growing in a mother's womb.

Once born, an infant may have a mass in their abdomen that can be felt. This mass represents the enlarged, swollen kidney.

Other potential symptoms of UPJ obstruction in an infant may include:

  • Blood in their urine (hematuria)
  • Poor growth and weight gain
  • Urinary tract infection

Possible Symptoms of Urinary Tract Infection in Infants

  • Fever (sometimes the only symptom)
  • Irritability
  • Foul-smelling urine
  • Poor feeding
  • Vomiting
  • Increased or decreased number of wet diapers
  • Discomfort with urination

Rarely, a baby will develop kidney failure—this is usually seen in infants born with only one kidney that is not blocked, or if UPJ blockage occurs in both kidneys.

Older Children and Adults

In older children and adults, (in which the congenital UPJ obstruction remained undiagnosed or is acquired), the following symptoms may occur:

  • Intermittent pain in the upper abdomen or back on the affected side that worsens when drinking a lot of fluids or caffeine (a natural diuretic)
  • Nausea and vomiting
  • Fatigue
  • Blood in the urine
  • Kidney stones develop as a result of the blockage
  • Urinary tract infections develop as a result of the blockage

In some cases, a patient has no symptoms of UPJ obstruction, but hydronephrosis is seen incidentally on an imaging test ordered for unrelated symptoms.


You have two bean-shaped organs called kidneys located in each flank, which is the area at the back of your abdomen, below your ribcage, and next to your spine.

Attached to each kidney is a long, thin tube called a ureter. The function of the ureter is to carry the urine produced in the kidney to the bladder, where it is eventually urinated out.

Ureteropelvic junction obstruction occurs when the junction (called the renal pelvis) that attaches the kidney to the ureter becomes blocked. This blockage either slows down or stops the normal flow of urine from the kidney to the bladder.

In most cases, the blockage is congenital, meaning some sort of abnormality within the kidney or ureter developed before birth. Much less commonly, UPJ obstruction is acquired.


The congenital abnormalities that may lead to UPJ obstruction include:

  • Kinking or twisting of the ureter
  • A ureter that inserts too high on the kidney
  • An abnormal or extra blood vessel that crosses in front of the renal pelvis and interferes with its functioning
  • An abnormal segment of the ureter that does not normally contract and relax (needed to push the urine along to the bladder)


Less commonly, the blockage is acquired and not present at birth.

This may occur as a result of the following:

  • Kidney stones
  • Scar tissue or damage from surgery
  • Cancer of the renal pelvis (this is rare)


While the diagnosis of UPJ obstruction may be suspected when hydronephrosis is seen as an ultrasound, other tests are needed to confirm the diagnosis.

Blood and Urine Tests

Various blood and urine tests will be ordered to evaluate a person's kidney function, including blood urea nitrogen (BUN) and creatinine clearance.

Additional Imaging Studies

Computed tomography (CT) scan or magnetic resonance imaging (MRI) studies may be ordered to better visualize the kidney and ureter and the associated blockage

Intravenous Pyelogram

Intravenous pyelogram is an X-ray test that visualizes dye (injected into a person's vein), as it is filtered from the bloodstream by the kidneys and passes through the ureters to the bladder.

Nuclear Renography

With nuclear renography, a patient will be given an intravenous (IV) radioisotope. Using a special camera, the radioisotope is watched as it is removed by the kidneys and passed through the ureter and bladder. The time it takes for the isotope to drain from the kidney is then measured. With a UPJ obstruction, the isotope will remain and not drain out rapidly (as it should).

Voiding Cystourethrogram

A voiding cystourethrogram is an X-ray test that visualizes whether dye injected into the bladder (through a catheter) refluxes back into the ureters and whether there are any blockages in the urethra. These two problems—called vesicoureteral reflux (VUR) and posterior urethral valves (PUV), respectively—are additional causes of hydronephrosis in infants.


Many cases of UPJ obstruction (especially in infants) improve and resolve on their own. During the watching and waiting time, antibiotics may be prescribed to prevent infection.

If the obstruction doesn't improve, which may cause chronic flank or abdominal pain, recurrent infections, worsening kidney function, and/or significant hydronephrosis, a surgery called pyeloplasty may be required.

Pyeloplasty entails reconstructing the renal pelvis, which is the attachment site of the ureter to the kidney, and the source of a UPJ obstruction.

The goals of pyeloplasty are to improve urine flow and reduce kidney damage and infection.

There are two types of pyeloplasty—open and laparoscopic. Laparoscopic pyeloplasty is the more common approach in adults.

Open pyeloplasty involves accessing the affected renal pelvis through a 2- to 3-inch cut in the abdomen, just below the ribcage.

With laparoscopic pyeloplasty, the UPJ is reached by making three very small (15 millimeters or so) cuts in the abdomen, underneath the ribcage. Various instruments are inserted through these small cuts in order to relieve the obstruction.

After surgery, follow-up care with periodic kidney ultrasounds and kidney function testing is required.

A Word From Verywell

If your baby has been diagnosed with UPJ obstruction, it's normal to feel anxious or scared. The good news, though, is that in many instances, this condition resolves on its own (sometimes even before birth), and if it doesn't, surgery is a very reasonable option with a high success rate.

5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  3. Krajewski W, Wojciechowska J, Dembowski J, Zdrojowy R, Szydelko T. Hydronephrosis in the course of ureteropelvic junction obstruction: An underestimated problem? Current opinions on the pathogenesis, diagnosis and treatment. Adv Clin Exp Med. 2017;26(5):857-864. doi:10.17219/acem/59509

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Additional Reading

By Colleen Doherty, MD
 Colleen Doherty, MD, is a board-certified internist living with multiple sclerosis.