Ureteropelvic junction obstruction (UPJO)
UPJO is the most common form of kidney obstruction. Nowadays most cases are diagnosed prenatally when a dilated kidney is noticed on routine ultrasounds. Some cases are diagnosed later in life because of recurrent episodes of back pain –on the side of the obstruction– sometimes associated with nausea and vomiting.
UPJO can be mild and go away on its own, but can also be severe and cause permanent renal damage.
How do doctors determine the severity of UPJO?
The 2 main tools to study UPJO are the renal ultrasound and the Mag 3 renal scan.
|Mild case||Severe case|
|Dilation||Center of kidney||Center and periphery|
|Kidney parenchyma (tissue)||Normal thickness||Thin|
|The width of the renal pelvis||<1.5 cm||>1.5 cm|
These parameters can be followed over time to determine if the problem is getting better or worse.
Mag 3 renal scan:
The Mag 3 renal scan provides more objective information but is more invasive than the renal ultrasound because the study requires an IV and a urethral catheter.
For this study, a substance called Mag 3 is injected into the patient IV. The Mag 3 is then is picked up and excreted by the kidneys. Multiple pictures are taken over time as the Mag 3 goes in and out of the kidneys. The scan can tell how much function the kidney has and how quickly the Mag 3 gets out of the kidney.
Normally, 50% of the Mag 3 goes to the right kidney and 50% goes to the left kidney. This is called the differential renal function (DRF). A DRF of less than 40% is considered abnormal. A drop of more than 10% over time (i.e 50% -> 45%) is considered significant.
The Mag 3 renal scan also measures the time it takes for the Mag 3 to leave the kidney: normally half of the mag 3 should be gone within 10 minutes. If the Mag 3 is not going anywhere, the radiologist injects a diuretic (Furosemide) to “push” the Mag 3 out of the kidney. If half of the mag 3 does not leave the kidney 20 minutes after the Furosemide injection that kidney is considered to be obstructed. We call this the diuretic half-life (T1/2). A T1/2 of 21 minutes is actually not too bad and will likely improve, however, an infinite T1/2 (no excretion whatsoever) is unlikely to improve.
Indications for Surgery for UPJO
These are common indications for surgery:
- Recurrent ipsilateral back pain, with or without nausea/vomiting
- Kidney infections
- Stone formation
- Worsening urinary tract dilation on serial renal ultrasounds
- Declining DRF
- Prolonged T1/2
The best reason to operate is for recurrent ipsilateral back pain associated with nausea/vomiting. This is a good reason because surgery will cure the problem >95% of the time. There are not so many surgeries that can cure like that!
Most urologists would agree to operate for infections, stones, or a significant and well document decline in the DRF.
Operating based on worsening dilation on serial ultrasounds can be somewhat subjective. Here you are likely to see more variability among urologists. The same goes for a prolonged T1/2, which tends to get better in most infants without surgery.
Patient is positioned on its side and taped to the bed.
The camera and surgical instruments are passed through 3-4 trocars:
The cause of the obstruction is identified and corrected:
- Instrinsic: there is a narrowed or diseased segment of the ureter at the UPJ. This segment is removed and the ureter and pelvis are put together again.
- Crossing vessels: an extra set of lower pole kidney vessels cause kinking of the ureter at the UPJ. The treatment is to cut the ureter, bring it above the vessels, and reattach it to the renal pelvis.
A ureteral stent is placed during the surgery to allow the repair to heal:
Most patients stay in the hospital overnight and go home before lunch the next day. The ureteral stent is removed under a brief anesthetic –1 minute long– 4 weeks after the surgery.
Here is a robotic pyeloplasty on a patient that was having recurrent ipsilateral back pain due to left obstructing vessels: