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
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.
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
Summary TableROC curve analysis of ΔCPR and ΔAPD and percent ΔCPR and percent ΔAPD in predicting
surgical outcome following pyeloplasty