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LETTER TO EDITOR
Year : 2020  |  Volume : 36  |  Issue : 4  |  Page : 334-335
 

Re: Elbaset MA, Ezzat O, Elgamal M, Sharaf MA, Elmeniar AM, Abdelhamid A et al. Supernormal differential renal function in adults with ureteropelvic junction obstruction: Does it really exist? Indian J Urol 2020;36:205-11


Department of Urology, Fortis Hospital Mulund, Mumbai and Chitale Clinic, Solapur, Maharashtra, India

Date of Submission20-Jul-2020
Date of Acceptance06-Aug-2020
Date of Web Publication1-Oct-2020

Correspondence Address:
Dr. Gyanendra R Sharma
Department of Urology, Fortis Hospital Mulund, Mumbai and Chitale Clinic, Solapur, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/iju.IJU_422_20

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How to cite this article:
Maheshwari PN, Sharma GR. Re: Elbaset MA, Ezzat O, Elgamal M, Sharaf MA, Elmeniar AM, Abdelhamid A et al. Supernormal differential renal function in adults with ureteropelvic junction obstruction: Does it really exist? Indian J Urol 2020;36:205-11. Indian J Urol 2020;36:334-5

How to cite this URL:
Maheshwari PN, Sharma GR. Re: Elbaset MA, Ezzat O, Elgamal M, Sharaf MA, Elmeniar AM, Abdelhamid A et al. Supernormal differential renal function in adults with ureteropelvic junction obstruction: Does it really exist? Indian J Urol 2020;36:205-11. Indian J Urol [serial online] 2020 [cited 2020 Oct 22];36:334-5. Available from: https://www.indianjurol.com/text.asp?2020/36/4/334/296769




Dear Sir,

We read with interest the article on supranormal differential renal function (snDRF) in adults by Elbaset et al. and congratulate the authors for the first such study reported in literature.[1] It is not uncommon in day-to-day practice to see patients presenting late in adulthood with hydronephrosis due to suspected pelviureteric junction obstruction. In this subset of patients, snDRF would compound the clinical dilemma regarding the presence of significant obstruction and differentiating it from a dilated nonobstructed system.

There are certain aspects of this study that need better understanding. It is generally agreed with the description by Koff that obstruction is best defined as any impediment to the drainage of urine from the kidney, which if not corrected would result in the deterioration of renal function.[2] In the present study, neither have Elbaset et al. clarified the indications for surgical intervention at late age nor have they explained why there was no functional deterioration in these patients despite late presentation of a congenital obstruction at an age of 36 ± 16 years.

The authors found that renal pelvis volume of 50 mm3 and anteroposterior diameter (APD) of 37 mm were associated with the highest sensitivity and specificity as far as the occurrence of snDRF was concerned. We would like to mention that the measurement of APD is affected by various factors such as the amount of hydration, fullness of bladder, and the position of the patient in which it is measured.[3] The authors have not explained how these factors were standardized during the study.

The authors conclude that their findings support the theory that snDRF is related to kidneys with large roomy renal pelvis with severe obstruction. Does this mean that all large renal pelvis will be associated with obstruction? By convention, t½ value >20 min is taken as an indicator of obstruction; however, there have been many studies which have shown that t½ values are fallacious due to the reservoir effect. Furthermore, there are many factors such as hydration, bladder fullness, and effect of gravity, which affect these values. We would like to state that t½ values alone are not good enough to diagnose obstruction, especially in large renal pelvis which are often complaint and at times are protecting the renal parenchyma from backpressure effects.[4]

There are parameters such as cortical transit time, which give a better idea regarding the excreting ability of the renal parenchyma and are more accurate in predicting the need for surgery. Furthermore, quantitative parameters such as output efficiency and normalized residual activity (NORA) have been shown to be more accurate renal emptying parameters as compared to t½.[4] NORA is calculated by dividing the uptake values at a given point, often at 60 min with the uptake value at 2 min.

We propose that it is important to look at some more parameters in these patients to differentiate patients who may be obstructed and need intervention from those who need follow-up alone. NORA is easy to calculate, does not need additional software, and can determine if the renal pelvic emptying is adequate. Percentage renal volume determined on magnetic resonance urography or computed tomography scan has been shown to correlate better with renal function. DMSA scan would be able to identify contradictory snDRF and assess the exact renal function.[5] These factors are important to use before decision of surgical intervention in patients with snDRF.

Financial support and sponsorship: Nil.

Conflicts of interest: There are no conflicts of interest.



 
   References Top

1.
Elbaset MA, Ezzat O, Elgamal M, Sharaf MA, Elmeniar AM, Abdelhamid A et al. Supernormal differential renal function in adults with ureteropelvic junction obstruction: Does it really exist? Indian J Urol 2020;36:205-11.  Back to cited text no. 1
  [Full text]  
2.
Koff SA. Problematic ureteropelvic junction obstruction. J Urol 1987;138:390.  Back to cited text no. 2
    
3.
Nguyen HT, Benson CB, Bromley B, Campbell JB, Chow J, Coleman B, et al. Multidisciplinary consensus on the classification of prenatal and postnatal urinary tract dilation (UTD classification system). J Pediatr Urol 2014;10:982-98.  Back to cited text no. 3
    
4.
Piepsz A. Antenatal detection of pelviureteric junction stenosis: Main controversies. Semin Nucl Med 2011;41:11-9.  Back to cited text no. 4
    
5.
Sarma D, Barua SK, Rajeev TP, Baruah SJ. Correlation between differential renal function estimation using CT-based functional renal parenchymal volume and (99 m)Tc-DTPA renal scan. Indian J Urol 2012;28:414-7.  Back to cited text no. 5
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