May also be called: UP Junction Obstruction; UPJ Obstruction; Obstruction of the Ureteropelvic Junction

Ureteropelvic (yuh-ree-tuh-roe-PEL-vik) junction obstruction is a partial or total blockage of the flow of urine (pee) in the area where a ureter attaches to a kidney. Ureters are the tubes that carry urine from the kidneys to the bladder.

More to Know

Kidneys filter waste products, salts, and excess water from the blood and produce urine. Ureters are the tubes that carry urine from the kidneys to the bladder, where it is stored until someone pees. Urine drains from the kidney through a structure called the renal pelvis, which attaches to the ureter at a point called the ureteropelvic junction, or UP junction.

If something blocks the flow of urine at the UP junction, it can cause a lump in the abdomen, bloody pee, back pain, pain in the sides, kidney infection, vomiting, or urinary tract infection (UTI), usually with a fever.

Most of the time, UP junction obstruction happens when a baby growing in the womb develops a UP junction that is too narrow. This causes urine to pool in the renal pelvis. Over time, this can damage the kidneys. Most babies with the condition are diagnosed before birth during prenatal ultrasound testing.

In older children and adults, UP junction obstruction can be caused by scar tissue, infections, kidney stones, or previous treatment for a blockage. The pooling of urine, called hydronephrosis (literally "water inside the kidney"), can be seen on a renal (kidney) ultrasound.

In many cases, UP junction obstruction in newborns improves on its own within the first 18 months of life. When treatment is needed, it usually involves surgery to remove the narrow UP junction and then reattach the ureter to the kidney.

Keep in Mind

A UP junction obstruction in a baby might cause no symptoms and need no treatment other than periodic checks to see how the kidney is functioning. Surgical treatment, when needed, is almost always successful and most children have no long-term complications.

All A to Z dictionary entries are regularly reviewed by KidsHealth medical experts.