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Urology

Ureteropelvic Junction (UPJ) Obstruction

Each of the two kidneys produces urine, which drips into a funnel-like structure called the renal pelvis. The urine travels from the pelvis into the ureter, a hollow tube (approximately the size of a piece of spaghetti) on its way to the bladder. The point where the ureter and pelvis meet is called the ureteropelvic junction (UPJ). When a blockage exists in the urinary system, this is its most common location. There are several causes of a UPJ obstruction. Some children have a ureter that is very narrow or strictured at the UPJ. Others have a ureter that inserts too high on the renal pelvis causing a kinking of the ureter. Still others have an extra blood vessel that goes to the lower pole of the kidney; in this situation, the ureter drapes over this vessel -- almost like a pair of pants draped over a hanger.

But the most common cause of UPJ obstruction is poor peristalsis. Peristalsis is the rhythmic propulsions of material similar to the way the intestines push food forward. In UPJ obstructions, urine often backs up in the kidney because the ureter at the UPJ lacks enough muscle fibers to push the urine forward. If surgery is necessary, removal of that lazy section or narrowed section of ureter will reestablish normal flow.

During pregnancy, the size of the renal pelvis is measured. The larger the pelvis, the more likely it is that a UPJ obstruction exists. However, if at term the renal pelvis is equal to or less than 10 mm, the chance of a significant obstruction requiring surgery is quite low.

Tests after the baby is born include repeat ultrasounds; possibly a voiding cystourethrogram (VCUG) to rule out reflux; and MAG-3 lasix washout renal scans to assess the kidney function and drainage. MAG-3 is an agent injected in a vein that travels to the kidney where it normally is quickly excreted. In an obstructed kidney, its drainage from the kidney is delayed. Some children may further require an intravenous pyelogram (IVP) or magnetic resonance imaging (MRI).

Most cases of hydronephrosis can be observed and they will gradually resolve over the first two to three years of life. However, if the hydronephrosis is pronounced and there is an obstruction at the UPJ, the obstructing segment will be surgically removed. This can be done typically via an incision in the flank or via robotic surgery. This procedure is called a pyeloplasty. The success rate for this procedure is approximately 95 percent.