Traditional teaching dictates performing a nephrectomy for hydronephrotic kidneys with <15% differential renal function (DRF) and a pyeloplasty for those with >15% DRF. This stems from the idea that poorly functioning kidneys don’t heal as well with a pyeloplasty and could eventually require a nephrectomy for persistent hydronephrosis or infections. The risk of a second surgery is not worth it for the poorly functioning kidney according to this line of reasoning.
Another approach proposed in the literature is placing e a nephrostomy tube on the poorly functioning kidney for 1 month and then repeating the functional study to determine if the function has improved; pyeloplasty is then done for kidneys that improved and nephrectomy for those who did not. However, this approach involves at least 2 general anesthetics, and 2 functional studies, compared to just one study and procedure if the surgery is performed primarily.
The advantage of a nephrectomy is that it eliminates the risk of requiring surgery in the future. The disadvantage is the possibility of removing a kidney that could have otherwise recovered some function with a pyeloplasty. If the patient then goes to develop renal failure as an adult, the extra 10-20% of kidney function could make a difference.
Technically, I personally think that a pyeloplasty is easier than a nephrectomy. There is a higher risk of significant bleeding during a nephrectomy –although rare.
Some kidneys recover significant function after a pyeloplasty and others loose function. This abstract found an overall 3% gain in function for pyeloplasties performed in poorly functioning kidneys. In the study, they had 3 patients with less than 10% function and 9 with 10-20% function. Both of these groups saw a mean post pyeloplasty improvement in function of 4-5%, compared to less than 3% improvement for kidneys with DRF in between 20-40%.
For poorly functioning kidneys ( <15%) observation makes a lot of sense. With only 4-5% gain in DRF to look forward to, the risk of surgery is certainly something to consider. I believe that observation is the best option for asymptomatic patients or those with mild to moderate hydronephrosis. I would also wait for at least 2 convincing episodes of pain before jumping into surgery for a poorly functioning kidney.
That been said, observation is more appropriate for an older child where DRF is likely to remain stable regardless, as opposed to a younger child where the little remaining kidney function could be completely lost.
The first case is a lesson in recognizing the limitation of the Mag 3 at determining DRF in poorly functioning kidneys.
This patient was evaluated with a renal ultrasound because of bilateral prenatal hydronephrosis and was found to have a left hydronephrotic kidney –likely from UPJ obstruction:
Mag 3 renal scan at 6 weeks of life demonstrated “7%” of function:
However, the final pictures of the Mag 3 fail to show any excretion of contrast on the left kidney, suggesting the 7% function might not be real:
Contrast that with another 7% functioning kidney, in an older child presenting with renal colic:
Notice in the image below how there is less background noise compared to the patient above, that suggests this patient 7% function is more real than then 7% function from the patient above:
But more importantly, notice in the image below how there is contrast accumulation in the poorly functioning kidney at the end of the study in this patient but not the patient above:
The first patient above underwent a pyeloplasty with complete resolution of the hydronephrosis:
Unfortunately, the kidney atrophied completely. Mag 3 revealed no detectable function postoperatively:
Despite the atrophy and lack of function, the hydronephrosis is gone and the patient has remained asymptomatic from that kidney.
The second patient has only had one episode of colic. She has not had anything done yet. I think observation or pyeloplasty would be appropriate options for the second patient, although nephrectomy would be the answer for the oral boards.
One more case
This patient was found to have 7% function on the right kidney at 6 weeks of life; after a month with a nephrostomy tube, DRF was 13%:
Because of the favorable change in DRF, the patient underwent a pyeloplasty. Although surgery went well and she has remained asymptomatic for several years now, the hydronephrosis did not change much. DRF has not been assessed postoperatively, but by the look of the kidney on the ultrasound, is likely the same — around 10%:
This last case highlights the fact that despite our best efforts, things might remain the same, and thus one should consider observation for most of these patients.
One can expect 4-5% improvement in DRF after a pyeloplasty for a kidney with less than 20% DRF– based on just on one study with only a few patients. When evaluating DRF, the static images provide partial information that should be complemented with the final images to assess for excretion. Observation is likely the best option for most asymptomatic poorly functioning kidneys. Pyeloplasty could be considered in symptomatic cases or those with good evidence of some function (clear uptake and some excretion) based on limited data, although my experience with it has been not the best. Nephrectomy is the option with the least amount of diagnostic and interventional procedures needed to take care of the problem in the long-term.