UPJ obstruction

Alternative names:

obstruction of the ureteropelvic junction; U-P junction obstruction; ureteropelvic junction obstruction

Definition:

An obstruction that forms at the area where the ureter attaches to the kidney pelvis.

Causes, incidence, and risk factors:

Ureteropelvic junction (UPJ) obstruction is generally a congenital condition caused by hardening (stenosis) that occurs at the junction of the ureter (muscular tube from the kidney to the bladder) and the pelvis of the kidney (the pelvis is the triangular collecting structure of the kidney). This blockage causes urine to collect in the pelvis of the kidney under pressure. The constant increased pressure causes damage to the kidney and loss of kidney structure. UPJ obstruction is the most frequently diagnosed cause of urinary obstruction in children.

UPJ obstruction is now commonly diagnosed during maternal ultrasound studies that show a dilated renal pelvis or "hydronephrosis." This condition, when recognized, is surgically corrected in the first few days after birth. Experimental decompression of the kidney has been tried with the fetus still in the uterus.

UPJ obstruction may be recognized after birth when an abdominal mass is found on examination, or if the infant develops a urinary tract infection associated with fever. Back pain and blood in the urine may also be signs of obstruction.