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Evaluation of renal function after pyeloplasty determined by 99mTc DTPA renogram

Background: Hydronephrosis (HDN) due to pelviureteric junction (PUJ) obstruction is a common congenital anomaly of urinary tract which is generally treated by pyeloplasty. But the extent of functional recovery is still debated. Considering the existing controversies, this study was designed to evaluate the changes of renal function after pyeloplasty measured by 99mTc-DTPA renography. Methods: This study was done in the department of urology, National Institute of Kidney Diseases and Urology (NIKDU) and Bangladesh Institute of Research and Rehabilitation in Diabetes, Endocrine and Metabolic Disorders (BIRDEM) General Hospital from July 2014 to December 2020. Sixty patients were included in this study and underwent Anderson-Hynes (A-H) dismembered pyeloplasty for PUJ obstruction. All patients were evaluated with diuretic 99mTc-DTPA renogoam before and at 3 and 6 months after pyeloplasty. Improvement of renal function was evaluated by comparing preoperative and postoperative differential renal function (DRF) and glomerular filtration rate (GFR). Results: Sixty patients (34 male and 26 female) with unilateral HDN due to PUJ obstruction were included in this study with mean age of 15.6 years (ranged from 3 – 38 years). Out of 60 patients, 56.7% had left sided HDN and 43.3% had right sided HDN. The mean preoperative DRF was 16.72 ± 8.35% at baseline which increased to 26.03 ± 7.08% at the end of 3rd month and 28.15 ± 5.84% at the end of 6th month. The mean preoperative GFR was 14.29 ± 6.73 ml/min/1.73 m 2 at baseline which increased to 24.13 ± 5.31ml/min/1.73 m 2 at the end of 3rd month and 27.38 ± 4.78 ml/min/1.73 m 2 at the end of 6th month. Conclusion: The result demonstrates that, after pyeloplasty renal function improves. Highest recovery of renal function noted in patients with poor pre-operative DRF and GFR.


INTRODUCTION
Hydronephrosis (HDN) due to pelviureteric junction (PUJ) obstruction is the most common upper urinary tract congenital anomaly that causes variable symptoms like flank pain, hematuria, urinary tract infection (UTI) and deterioration of renal function. It is reported to occur in 1:500 to 1:1250 live births. 1 Widespread use of perinatal ultrasonography (USG) and the advancement of new imaging modalities contributed to earlier diagnosis of childhood HDN. As majority of the infants are asymptomatic, it is important to assess the extent of anatomical and functional deterioration of the hydronehrotic kidney. 2 For evaluation of obstruction and renal function (RF) intravenous urography (IVU) and diuretic renography are done. The initial differential renal function (DRF) and the time activity curve in diuretic renogram of the affected kidney help to determine the treatment protocol. 3,4 PUJ obstruction is treated surgically and early intervention prevents potential complications. 2 Anderson-Hynes (A-H) dismembered pyeloplasty is the commonly employed surgical procedure for correction of this problem. Success is defined as resolution of symptoms and stabilization or improvement in function on diuretic renogram. 5 After pyeloplasty, improvement of renal function depends on multiple factor like, degree of obstruction 4 , duration of obstruction 6 , preoperative DRF on radionuclide renogram 7,8 , renal cortical thickness 8 and the age of patient at the time of relief of obstruction. 9 As pelviectasis and caliectasis both may exist in an unobstructed system, ultrasonography (USG) and intravenous urography (IVU) do not provide adequate early postoperative functional assessment. 10 In contrast, diuretic renography offers a truly quantifiable assessment of renal function that can be objectively compared with the preoperative scan. Moreover, persistent obstruction can be detected promptly to allow further intervention. This study was designed to evaluate the changes of renal function after pyeloplasty measured by 99mTc-DTPA renography.

METHODS
This multicenter prospective quasi experimental study was conducted in the department of Urology, NIKDU and BIRDEM from July 2014 to December 2020. Patients with unilateral HDN due to PUJ obstruction, with or without any complication attending in the urology outdoor and consented for the study, were admitted in different urology units. Patients with bilateral HDN, HDN due to vesicoureteral reflux (VUR) and recurrent PUJ obstruction were excluded. We divided our study population in different groups in respect of preoperative DRF and GFR. Under general anaesthesia, retrograde pyelography (RGP) was done. Then A-H pyeloplasty was carried out by retro-peritoneal flank approach, over a D-J stent. After 6 weeks, D-J stents were removed as an outpatient procedure. During their follow up, after 3 and 6 month, every patient was evaluated by taking history, clinical examination and 99mTc-DTPA renogram. Data were collected on variables of interests and were analyzed using chi-square (F 2 ) test, ANOVA and Wilcoxon Signed Rank Test. For all analytical tests, the level of significance was set at 0.05 and p value <0.05 was considered significant.

RESULTS
In present study, mean age of the patients was 15.6 years, ranged from 3 -38 years. It was observed that the highest frequency of patients (36.7%) was in the age group 10 -20 years. Over one quarter (33.3%) of patients was below 10 years of age and 30.0 % was above 20 years.         Patients with preoperative DRF <20% exhibited significant improvement at 6 month compared to other patients who had initial DRF more than that.
In the series of Harraz et al. 8 their primary outcome measures were greater than 5% improvement in baseline DRF. They found that, DRF was more likely to improve when preoperative DRF was less than 40%. This could be explained by the fact that, in patients with lower baseline DRF there is more space for the kidney to recover than in those with better baseline DRF. Their result was consistent with Almodhen et al. 11 In their series none of 49 patients with baseline DRF greater than 45% achieved more than 5% improvement postoperatively compared to 43% with baseline DRF less than 45%, who achieved greater than 5% improvement. Our result is also consistent with earlier studies. Wagner et al. 12 studied with 32 children with unilateral hydronephrosis due to PUJ obstruction. Among three groups, patient with initial DRF <10% showed highest improvement (DRF 53%) on 12 month follow-up and supports their approach of performing pyeloplasty in patients even with an initial DRF of <10 %. Our finding also matches with Abdelaziz 13 where pyeloplasty provides high rates of functional recovery in very poorly functioning kidneys with DRF dŠ10% in pediatric age group. So the finding of higher recovery or improvement of renal function with initial lower DRF in this study is consistent with previous works.
The work of Materny et al. 14 showed that, when preoperative and consecutive postoperative DRF values did not reveal any significant differences, a progressive increase in GFR was noted at three months from surgery, which becomes most significant after 12 months.
DRF calculated by 99m Tc-DTPA, 99m Tc-MAG3, and 99m Tc-DMSA renogram can be used reliably and each method gives similar measures. 15 Among these 99m Tc-DTPA renogram is most widely available and cheap. So, we picked it as our quantification tool.
Reis et al. 16 enquired about adequacy of follow-up length in patients undergoing pyeloplasty. They studied 28 patient ( mean age 2.4 years ) for >5 years and concluded that, satisfactory diuretic renogram at 3 to 6 months after pyeloplasty with maintained renal function and stable hydronephrosis suggests no need for further follow-up and indicates no functional loss with time. In view of this study, the follow-up period of 6 month of our study is justified.

Conclusion
This study clearly demonstrates that, renal function improves after A-H pyeloplasty, as measured by 99m Tc-DTPA renogram. Rapid and significant functional improvement occurs by 3 months and a small improvement continued thereafter. Maximal improvement of renal function is noted in patients with poor pre-operative DRF and GFR.

Limitation of the study
There are few limitations of this study like, small sample size and pyeloplasties were done by different surgeons from different urology units.

Recommendations
In the light of observation and results of the study, it can be inferred that, pyeloplasty results in renal functional improvement which is most marked in poorly functioning kidneys. Early pyeloplasty can prevent future deterioration of renal function and can help to reduce the number of nephrectomies.