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What Causes UPJ Obstruction?

Anatomy of Ureteropelvic Junction Obstruction (UPJ)
Anatomy of Ureteropelvic Junction Obstruction (UPJ)
Image © 2003 Fairman Studios, LLC.

Most often UPJ obstruction is congenital. This means that children are born with this health issue. It is not known how to prevent it. One in 1,500 children are born with this problem. The blockage occurs as the kidney is forming. Today most cases are found using ultrasound before birth. Though it occurs less often in adults, UPJ obstruction may happen after kidney stones, surgery or upper urinary tract swelling.

In UPJ obstruction, the kidney makes urine faster than it can be drained through the renal pelvis into the ureter. This causes urine to pool in the kidney, which leads to kidney swelling (hydronephrosis). Often, only 1 kidney is affected. The enlarged kidney is easily seen on ultrasound. For this reason, a doctor can often predict UPJ obstruction before a baby is born.