THE UTILITY OF RENAL SONOGRAPHIC MEASUREMENTS IN DIFFERENTIATING CHILDREN WITH HIGH GRADE CONGENITAL HYDRONEPHROSIS
Christopher S. Cooper, M.D., Tomas Lence, B.A., Gina M. Lockwood, M.D., Douglas W. Storm, M.D., Caitlin E. Ward, B.A..
University of Iowa, Iowa City, IA, USA.
BACKGROUND: Current grading systems for hydronephrosis include a subjective determination of parenchymal ‘thickness’ and suffer from poor reliability. Use of more objective ultrasonographic measurements including renal medullary pyramidal thickness (PT) may be useful in augmenting current grading systems by decreasing subjectivity and enhancing prognostic ability. To evaluate the utility of PT measurements in patients with SFU grades 3 and 4 hydronephrosis, we assessed the: 1) the inter-rater reliability of PT measurements, 2) the correlation between relative renal function on nuclear renal scan and PT, and 3) the pyeloplasty predictive ability of PT alone and in combination with SFU grade and/or other sonographic measurements in multivariate statistical models. METHODS: We retrospectively reviewed 110 children (125 renal units) with isolated SFU grade III and IV hydronephrosis at median age (IQR) of 1.7 months (0.6-5.2). The PT, APD, and renal length were measured on sonographic images. Receiver operating characteristic (ROC) curves were generated for inclusive multivariate models for prediction of pyeloplasty. RESULTS: Sixty-two kidneys were followed without operative intervention while 63 underwent pyeloplasty. Indications for surgery included an obstructive drainage pattern with a T1/2 >20 minutes on diuretic renal scan in addition to decreased relative renal function less than 40%, increasing hydronephrosis on serial ultrasounds, and/or a decline in relative renal function >10% on serial renal scans. The median age at the time of pyeloplasty was 5.7 months (2.8-13.7). The median time from initial presentation to final follow-up for all patients was 28 months (18.3-44.6). The inter-rater reliability for SFU grading was only fair (Fleiss kappa value = 0.369 (95% CI: 0.26-0.479)) whereas it was excellent for PT measurements (0.914 (95% CI: 0.856-0.954)). A PT > 3mm occurred significantly more frequently in kidneys with a DRF >= 45% (p= 0.0056). PT alone was predictive of subsequent pyeloplasty (AUC=0.781) and a PT cutoff at 3mm identified 73% of kidneys managed by pyeloplasty and correctly ruled out 74%. A novel multivariate pyeloplasty predictive score (PPS) using only objective measurements including PT, APD, and relative renal length was as accurate as a PPS that incorporated SFU grade (AUC of 0.885 and 0.866, respectively). Conclusions: PT is a useful measurement to characterize hydronephrotic kidneys with calyceal dilation. The inter-rater reliability of PT was excellent, and both PT alone and in addition to other variables including the SFU grade demonstrated that PT provides additional prognostic information regarding the risk of a pyeloplasty. In addition, a PT > 3mm was strongly associated with differential renal function > 45% in patients with unilateral hydronephrosis. Similar to previous publications, the SFU grading system was noted to have only fair inter-rater agreement, and since PT has excellent inter-rater agreement and is more objective than the subjective impression of parenchymal ‘thickness’, utilization of PT < 3mm as criteria for ‘thinned parenchyma’ in the SFU, UTD, and other hydronephrosis grading systems should be considered.
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