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 two ureters. 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.

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.

There are a number of different types of obstructions that may be present at birth, as follows:

  • 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, or swelling in the urinary tract.

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.

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 is not 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

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