Differential renal length index: useful measure in management of isolated unilateral hydronephrosis?

OBJECTIVE: To explore the usefulness of the 'differential renal length index' (iDRL) before and after pyeloplasty, as the anteroposterior diameter is commonly used to quantify hydronephrosis but inaccuracies arise due to interobserver variability, hydration status and pure intra-renal dilatation. PATIENTS AND METHODS: Prospectively collected data, from two centres, of all children undergoing pyeloplasty for isolated unilateral pelvi-ureteric junction obstruction (PUJO) (2015-2021) were analysed. Subgroup analysis was undertaken: Group A - differential renal function (DRF) ≥40%, Group B - subnormal DRF (20-39%), and Group C - symptomatic. Children with structural anomalies of upper and lower urinary tract, bilateral involvement, and subnormal DRF (<20%) were excluded. All the children had a pre- and postoperative ultrasound scan and Tc99m mercapto-acetyltriglycine (MAG3) renograms. The iDRL was calculated as follows: iDRL = ([a - b]/b) × 100, where 'a' is the length of hydronephrotic kidney (cm) and 'b' is the length of contralateral normal kidney (cm). The mean difference and standard error of mean (SEM) between the pre- and postoperative iDRL was evaluated using the paired Student's t-test, with P < 0.05 considered statistically significant. RESULTS: A total of 119 children with 1-year follow-up were included. For the entire cohort, the mean (SEM) preoperative iDRL was 27.7 (1.4) and postoperatively was 12.5 (1.1), with a mean (range) DRF improvement of 54% (44-66%) (P < 0.001). In Group A (n = 97), the mean (SEM) preoperative iDRL was 26.6 (1.5) and postoperatively was 13.1 (1.2), with a mean (range) DRF improvement of 50% (38-63%) (P < 0.001). In Group B (n = 22), the mean (SEM) preoperative iDRL was 32.6 (3.5) and postoperatively was 10.0 (2.8), with a mean (range) DRF improvement of 69% (49-89%) (P < 0.001). In Group C (n = 28), the mean (SEM) preoperative iDRL was 19.9 (2.3) and postoperatively was 7.7 (1.9), with a mean (range) DRF improvement of 61% (38-85%) (P < 0.001). CONCLUSION: Our study identifies the iDRL as a useful measure of improvement following successful pyeloplasty. In the subgroup with DRF of >39% minimum improvement was >37%. Similar minimum DRF improvement was also noted (>37%) in hypo-functioning kidneys and symptomatic PUJO.

Calyx to Parenchymal Ratio (CPR): An unexplored tool and its utility in the follow-up of pyeloplasty.

INTRODUCTION: Antero-posterior trans pelvic diameter (APD) and renal scintigraphy play a significant role in the diagnosis of pelvi-ureteric junction (PUJ) obstruction and postoperative follow-up following pyeloplasty. However, the APD varies irrespective of improvement, deterioration, or preserved function in a hydronephrotic kidney and is not a reliable parameter due to various factors (hydration status, compliance, and reduction pyeloplasty). Calyx to Parenchymal Ratio (CPR) is the ratio of the depth of the calyx and parenchymal thickness measured on ultrasound (USG) in coronal image. We assessed the utility of CPR in the follow up of pyeloplasty and compared it with the commonly used APD of the pelvis and renal scintigraphy. MATERIAL AND METHODS: A prospective cohort study was done from July 2016 to October 2017. During this period 73 pyeloplasties were done, and 62 cases meeting the inclusion criteria were enrolled. All the children underwent ultrasound and Technetium-99 m Ethylene dicysteine isotope renogram (EC) scan before and after pyeloplasty. APD and CPR values were measured on USG and compared with isotope renogram outcomes in these children in the preoperative versus postoperative period. Two defined objective variables ΔAPD, percent ΔAPD and ΔCPR, percent ΔCPR were compared with categorical variables that would predict the surgical outcome as - failed, successful or equivocal. Multinomial logistic regression analysis and receiver operating curve (ROC) analysis was used to identify predictive accuracy. RESULTS: The mean (range) APD value recorded in the preoperative period was 3.67 cm (1.40-8.00 cm), which decreased to 1.67 cm (0.40-6.50) postoperatively, which was 54.2% lower (P=<0.001). The mean (range) CPR value decreased from 5.96 (1.20-20.00) in the preoperative period to 2.57 (0.43-10.90) postoperatively, which was 56.8% lower (P=<0.001). On multinomial logistic regression analysis, ΔCPR was found to be a significant predictor of outcome with an overall accuracy of 95.1%, change in CPR was a better predictor of success after pyeloplasty as compared to change in APD, which had an overall accuracy of 85.2% (p = 0.01). Further, on ROC curve analysis, we observed that ΔCPR and %ΔCPR can strongly predict successful pyeloplasty with a sensitivity of each with 96% and 98% respectively and AUC of 0.897 and 0.799 respectively. DISCUSSION: USG (APD) and renogram are the most widely used investigation in follow-up of pyeloplasty; however, APD has its own limitations like operator variability and slower improvement. CPR has the advantages that neither calyceal depth nor parenchymal thickness is directly altered during the surgery, and early resolution of calyceal dilatation and rapid parenchymal growth following pyeloplasty and thus a surgeon independent parameter. Our results have shown that ΔCPR can identify successful pyeloplasty with strong prediction than ΔAPD and thus renal scans can be avoided if there is visible improvement in CPR on follow-up. CONCLUSIONS: Our study identified a change in CPR, i.e., ΔCPR as a strong predictor of surgical outcome, as it is not influenced by extent of pelvis reduction during pyeloplasty and early to change. Using this parameter, we can avoid unnecessary repeated nuclear scans based on persistent high APD values and optimize resource utilization. We recommend the use of CPR in routine practice in the preoperative and postoperative follow-up of PUJ obstruction following pyeloplasty.