Modified Grading of Postnatal Urinary Tract Dilation

Abstract

Source: Melo FF, Vasconcelos MA, Mak RH, et al. Postnatal urinary tract dilatation classification: improvement of the accuracy in predicting kidney injury [pubished online ahead of print August 28, 2021]. Pediatr Nephrol. doi: 101007/s00467-021-05254-xInvestigators from the Federal University of Minas Geraos (UFMG), Belo Horizonte, Brazil, and Rady Children’s Hospital, San Diego, CA, conducted a study to assess the accuracy of multiple classification systems for urinary tract dilatation (UTD) on postnatal ultrasound (US) in predicting future need for surgical intervention and/or kidney injury among neonates diagnosed with antenatal hydronephrosis (ANH). Study participants were infants with isolated ANH, defined as anteroposterior renal pelvis diameter ≥5 mm on a third trimester ultrasound, who were seen at the Pediatric Nephrology Unit at UFMG and followed prospectively from 1989 to 2019. The initial postnatal US was performed at approximately 14 days of age. A standard protocol was used to manage these patients. Study outcomes were surgical intervention and kidney injury. The need for surgery was determined using a protocol with markers indicative of severe obstruction, and kidney injury was defined as the presence of significant proteinuria, hypertension, or presence of chronic kidney disease (CKD). Using the results of the first postnatal US, severity of UTD was categorized using 5 grading systems: renal pelvic diameter (RPD), renal parenchyma thickness (RPT), a grading system developed by the Society of Fetal Urology (SFU), the UTD grading system, and a modified UTD system (UTDm). The accuracy of each system for predicting each outcome was assessed by generating receiver operating curves (ROC) and measuring the area under the curve (AUC). In addition, using the ROC analysis, the threshold (measurement with RPD and RPT and grade with the other tests) that maximized sensitivity and specificity was identified.Data were analyzed on 447 children, including 318 (71.1%) boys. Median follow-up was 9 years. Overall, 131 (29%) underwent surgical intervention at a median age of 8 months. The AUC for all grading systems in predicting surgical intervention were all >0.90, but the AUC for RPT statistically was significantly worse than that of the other tests. Using a threshold of >grade 2 with UTDm, the sensitivity for surgery was 85.5% and specificity was 89.9%. For RPD, a cutoff value of >15 mm had a sensitivity of 99.2% and specificity of 82.3%. A total of 26 children (5.8%) met criteria for kidney injury. The highest AUCs for predicting kidney injury were achieved with RPT (AUC = 0.921) and UTDm (AUC = 0.913); RPD and SFU had significantly worse AUCs. The sensitivity and specificity of UTDm, with a threshold at grade 2 or higher for predicting kidney injury, were 100% and 71.9%, respectively, and for RPT, with a cutoff at ≤8.9 mm, 96.1% and 80.0%, respectively.The authors conclude that several grading systems for UTD in newborns with ANH have good accuracy in predicting need for surgery and/or kidney injury.Dr Sanchez-Kazi has disclosed no financial relationship relevant to this commentary. This commentary does not contain a discussion of an unapproved/investigative use of a commercial product/device.Hydronephrosis as a congenital anomaly of the kidney and urinary tract can affect up to 14% of all pregnancies.1 Kidney and bladder US is used for grading the degree of UTD and for measurement of the RPT. Several grading systems are used today, including the SFU, UTD Consensus Recommendations, and Onen’s (2–4). The researchers in the current study combined the grading systems with some modifications to enhance the sensitivity and specificity of using hydronephrosis and RPT in predicting long-term kidney injury.The current study is 1 of the few with long-term follow-up of the hydronephrotic kidney and the participants’ blood pressure, urine protein, and kidney function. As with previous reports, kidney outcomes are easier to predict with mild and severe hydronephrosis (See AAP Grand Rounds. 2020;43[4]:42.)5 Moderate degree of hydronephrosis needs more follow-up and requires further imaging to assess if and when surgical intervention is required. Quantitative information such as RPT is useful in addition to grading of UTD. The difficulty in using the grading systems, however, is not the quantification, but standardization of where the measurements should be obtained since dilation can be affected by hydration and bladder fullness.Past studies have shown significant intra- and interobserver variability between clinicians.6,7 It is interesting to note that the number of surgical interventions was higher in the early years of the current study period. Does this reflect changes in indications for surgery, improvement in grading and measurement of the urinary dilation, or changing attitudes toward early surgical intervention?Modifications of the current postnatal US grading systems are useful in prognostication of kidney health in infants with antenatal onset of hydronephrosis.Recall that isolated ANH has a high rate of spontaneous resolution, thus abrogating the need for extensive imaging or urological intervention.5