Ureteropelvic junction (UPJ) obstruction

What is UPJ obstruction?

Urine made in the kidney collects in the renal pelvis and from there travels down the ureter to the bladder. The point where the renal pelvis joins the ureter is called the ureteropelvic junction. When this junction is narrow, urine cannot drain easily from the pelvis, and the pelvis and calyces become dilated. This is called ureteropelvic junction obstruction (UPJ obstruction).

It is the most common cause of hydronephrosis that needs surgery in children. It occurs in about 1 in every 1000–1500 children and is more common in boys and in the left kidney. In about 10–40% of cases it can be on both sides.

Causes

• Intrinsic narrowing. In the junction area, the muscle structure of the ureter wall does not develop properly and cannot push urine along. This is the most common cause in babies.
• Compression by a blood vessel. An extra vessel going to the lower pole of the kidney crosses over the ureter and compresses it. This is seen more often in older children and teenagers.
• High insertion, adhesions, kinks. The ureter leaving the pelvis at a point higher than normal, or being stuck to the surrounding tissue.

Symptoms

Today, in most children UPJ obstruction is found during pregnancy on fetal ultrasound, and there are no complaints after birth.

In cases not found during pregnancy, these signs may appear:

• Recurrent abdominal or flank pain, often with vomiting. The pain typically starts after drinking a lot of fluid (this is called Dietl’s crisis),
• febrile urinary tract infection,
• blood in the urine, especially after a minor blow,
• kidney stones,
• a lump that can be felt in a baby’s abdomen (very rare, in very severe dilation).

Diagnosis

• Kidney ultrasound. Dilation of the pelvis and calyces, thickness of the kidney tissue. If the ureter is not dilated, the narrowing is likely to be exactly at the junction of the pelvis and ureter.
• MAG3/DTPA renogram. This is the main test. It shows each kidney’s share of total function and how quickly urine drains from the pelvis. Normally each kidney’s share is about 45–55%.
• VCUG (voiding cystourethrogram). Since some children also have reflux, it may be ordered, especially if there has been a febrile infection.
• MR urography. If the anatomy is unclear, or if vessel compression or a complex anomaly is suspected.

Treatment

Monitoring

For most children whose condition was found in pregnancy, whose kidney function is preserved and who have no symptoms, active monitoring is chosen first. Ultrasound is repeated regularly, and MAG3/DTPA is repeated when needed. In some of these children drainage improves over time and surgery is not needed.

When is surgery needed?

• the kidney’s share is below 40% or drops by more than 10% during monitoring,
• the dilation increases on ultrasound or the kidney tissue becomes thinner,
• there are symptoms such as pain, febrile infection or stones,
• in a solitary kidney or in severe narrowing on both sides.

Pyeloplasty

The standard operation is pyeloplasty (Anderson-Hynes technique): the narrow segment is removed and the ureter is reattached to the pelvis with a wide opening. The operation can be done open, laparoscopically or robotically. The success rate is high with all approaches, over 90–95%.

Follow-up after surgery

After surgery, ultrasound is repeated several times during the first year, and MAG3/DTPA is done 6–12 months later when needed. A gradual decrease in dilation and preserved kidney function show that treatment has been successful. Full normalization of the measurement takes months, sometimes years.