Ureteropelvic Junction (UPJ) Obstruction

Urine produced in the kidney first passes through small ducts into the kidney's collecting basin (renal pelvis), from where it is carried in turn to the ureter (urinary duct) and the bladder and then expelled. The point where the renal pelvis joins the ureter is called the "ureteropelvic junction".

A narrowing at this transition point between the renal pelvis and the ureter (urinary duct), caused by congenital developmental abnormalities, is called ureteropelvic junction obstruction (UPJ obstruction or kidney outlet obstruction). This narrowing impairs the flow of urine, and urine accumulating in the kidney causes dilation of the renal pelvis and collecting system (hydronephrosis). If the narrowing seriously disrupts urine flow, over time it can lead to a decline in kidney function and even complete loss of kidney function.

How Common Is It?

In babies found to have kidney dilation (hydronephrosis) before birth, UPJ obstruction is the most common cause of this dilation. It is seen in approximately 1 in 1,500 births. It is usually on the left side and is twice as common in boys.

What Causes It?

It is most often a congenital condition. It results from abnormalities in the development of the structures that form the kidney and urinary ducts, known as the ureteric bud and the metanephric blastema. In addition, abnormally developed kidney vessels crossing the UP junction, or a UP junction that exits higher than it normally should, can cause congenital UPJ obstruction.

Apart from congenital abnormalities, previous infections (especially tuberculosis), trauma and surgery can cause acquired UPJ obstruction.

How Is It Diagnosed?

The diagnosis is usually made by ultrasound during routine pregnancy screening, that is, while the baby is still in the womb. Some cases are detected years later, even in adulthood, through imaging performed because of pain, urinary infection or another reason. In cases diagnosed with UPJ obstruction on imaging, a kidney scan (diuretic renogram with DTPA or MAG-3) is performed to determine the severity of the narrowing and to decide whether surgery is needed. Early diagnosis and treatment of severe obstruction is very important for preserving kidney function.

Who Should Be Treated?

If kidney function is impaired (<40%) or decreases by more than 10% during follow-up,

If drainage is poor despite the medication given during the diuretic renogram,

If it causes persistent pain and infections

How Is It Treated?

The treatment of UPJ obstruction is surgical. In the operation called pyeloplasty, the narrowed UP junction is removed and the renal pelvis is sewn back onto the ureter. This can be done by open, laparoscopic or robotic surgery. Laparoscopic and robotic surgery offer advantages over open surgery in terms of cosmetic outcome and recovery.

In people who have previously had an unsuccessful pyeloplasty, endopyelotomy, performed endoscopically, is another surgical technique used to treat this condition.