Renal parenchymal area and risk of ESRD in boys with posterior urethral valves

Fully automated kidney image biomarker prediction in ultrasound scans using Fast-Unet+

Any kidney dimension and volume variation can be a remarkable indicator of kidney disorders. Precise kidney segmentation in standard planes plays an undeniable role in predicting kidney size and volume. On the other hand, ultrasound is the modality of choice in diagnostic procedures. This paper proposes a convolutional neural network with nested layers, namely Fast-Unet++, promoting the Fast and accurate Unet model. First, the model was trained and evaluated for segmenting sagittal and axial images of the kidney. Then, the predicted masks were used to estimate the kidney image biomarkers, including its volume and dimensions (length, width, thickness, and parenchymal thickness). Finally, the proposed model was tested on a publicly available dataset with various shapes and compared with the related networks. Moreover, the network was evaluated using a set of patients who had undergone ultrasound and computed tomography. The dice metric, Jaccard coefficient, and mean absolute distance were used to evaluate the segmentation step. 0.97, 0.94, and 3.23 mm for the sagittal frame, and 0.95, 0.9, and 3.87 mm for the axial frame were achieved. The kidney dimensions and volume were evaluated using accuracy, the area under the curve, sensitivity, specificity, precision, and F1.

Congenital anomalies of the kidney and urinary tract: defining risk factors of disease progression and determinants of outcomes

Congenital anomalies of the kidney and urinary tract (CAKUT) result from disruptions in normal kidney and urinary tract development during fetal life and collectively represent the most common cause of kidney failure in children worldwide. The antenatal determinants of CAKUT are diverse and include mutations in genes responsible for normal nephrogenesis, alterations in maternal and fetal environments, and obstruction within the normal developing urinary tract. The resultant clinical phenotypes are complex and depend on the timing of the insult, the penetrance of underlying gene mutations, and the severity and timing of obstruction related to the sequence of normal kidney development. Consequently, there is a broad spectrum of outcomes for children born with CAKUT. In this review, we explore the most common forms of CAKUT and those most likely to develop long-term complications of their associated kidney malformations. We discuss the relevant outcomes for the different forms of CAKUT and what is known about clinical characteristics across the CAKUT spectrum that are risk factors of long-term kidney injury and disease progression.

Kidney length standardized to body length predicts outcome in infants with a solitary functioning kidney

BACKGROUND

Infants with a solitary functioning kidney (SFK) are at risk for chronic kidney injury (CKI). Lack of compensatory kidney growth (CKG) is associated with CKI, but measuring CKG is challenging since it is typically reported relative to normal kidneys. This study aims to (1) standardize SFK growth in infants, (2) investigate the relationship between standardized kidney length and clinical outcomes, and (3) use these results to develop a risk-based prediction model and local clinical pathway for SFK care.

METHODS

This was a quality improvement study of 166 infants with an SFK. Linear regression was used to assess kidney growth from 0 to 180 days of life. Univariate binary regression analysis was used to identify kidney length to body length thresholds associated with the development of CKI, defined as the composite outcome of chronic kidney disease (eGFR < 60 mL/min/1.73 m²), hypertension, or proteinuria.

RESULTS

Kidneys grew in length from 0 to 180 days, and growth was constant when standardized to body length. Over follow-up, infants with a baseline kidney length to body length ≤ 0.088 were more likely to experience CKI than the rest of the cohort (27 vs. 8%, p = 0.04). Kidney length to body length ≤ 0.088 was also significantly associated with CKI development (OR 4.17, 95% CI 1.14-15.28, p = 0.04).

CONCLUSIONS

In this study, kidney length to body length ratio was a stable CKG metric over 0-180 days, and a baseline ratio ≤ 0.088 was a risk factor for CKI. Results will aid in developing a practical, point-of-care risk assessment tool, and overarching risk-stratified clinical pathway for infants with an SFK. A higher resolution version of the Graphical abstract is available as Supplementary information.

Deep-learning segmentation of ultrasound images for automated calculation of the hydronephrosis area to renal parenchyma ratio

Purpose

We investigated the feasibility of measuring the hydronephrosis area to renal parenchyma (HARP) ratio from ultrasound images using a deep-learning network.

Materials and Methods

The coronal renal ultrasound images of 195 pediatric and adolescent patients who underwent pyeloplasty to repair ureteropelvic junction obstruction were retrospectively reviewed. After excluding cases without a representative longitudinal renal image, we used a dataset of 168 images for deep-learning segmentation. Ten novel networks, such as combinations of DeepLabV3+ and UNet++, were assessed for their ability to calculate hydronephrosis and kidney areas, and the ensemble method was applied for further improvement. By dividing the image set into four, cross-validation was conducted, and the segmentation performance of the deep-learning network was evaluated using sensitivity, specificity, and dice similarity coefficients by comparison with the manually traced area.

Results

All 10 networks and ensemble methods showed good visual correlation with the manually traced kidney and hydronephrosis areas. The dice similarity coefficient of the 10-model ensemble was 0.9108 on average, and the best 5-model ensemble had a dice similarity coefficient of 0.9113 on average. We included patients with severe hydronephrosis who underwent renal ultrasonography at a single institution; thus, external validation of our algorithm in a heterogeneous ultrasonography examination setup with a diverse set of instruments is recommended.

Conclusions

Deep-learning-based calculation of the HARP ratio is feasible and showed high accuracy for imaging of the severity of hydronephrosis using ultrasonography. This algorithm can help physicians make more accurate and reproducible diagnoses of hydronephrosis using ultrasonography.

Automated measurement of total kidney volume from 3D ultrasound images of patients affected by polycystic kidney disease and comparison to MR measurements

PURPOSE

Total kidney volume (TKV) is the most important imaging biomarker for quantifying the severity of autosomal-dominant polycystic kidney disease (ADPKD). 3D ultrasound (US) can accurately measure kidney volume compared to 2D US; however, manual segmentation is tedious and requires expert annotators. We investigated a deep learning-based approach for automated segmentation of TKV from 3D US in ADPKD patients.

METHOD

We used axially acquired 3D US-kidney images in 22 ADPKD patients where each patient and each kidney were scanned three times, resulting in 132 scans that were manually segmented. We trained a convolutional neural network to segment the whole kidney and measure TKV. All patients were subsequently imaged with MRI for measurement comparison.

RESULTS

Our method automatically segmented polycystic kidneys in 3D US images obtaining an average Dice coefficient of 0.80 on the test dataset. The kidney volume measurement compared with linear regression coefficient and bias from human tracing were R² = 0.81, and - 4.42%, and between AI and reference standard were R² = 0.93, and - 4.12%, respectively. MRI and US measured kidney volumes had R² = 0.84 and a bias of 7.47%.

CONCLUSION

This is the first study applying deep learning to 3D US in ADPKD. Our method shows promising performance for auto-segmentation of kidneys using 3D US to measure TKV, close to human tracing and MRI measurement. This imaging and analysis method may be useful in a number of settings, including pediatric imaging, clinical studies, and longitudinal tracking of patient disease progression.

Ultrasound-Based Renal Parenchymal Area and Kidney Function Decline in Infants With Congenital Anomalies of the Kidney and Urinary Tract

Congenital anomalies of the kidney and urinary tract are the leading cause of chronic kidney disease in children. Noninvasive imaging biomarkers that predict chronic kidney disease progression in early infancy are needed. We performed a pilot study nested in the prospective Chronic Kidney Disease in Children cohort study to determine the association between renal parenchymal area (RPA) on first post-natal renal ultrasound and change in estimated glomerular filtration rate (eGFR) in children with congenital anomalies of the kidney and urinary tract. Among 14 participants, 78.6% were males, the median age at the time of the ultrasound was 3.4 months (interquartile range, 1.3-7.9 mo), and the median total RPA z-score at baseline was -1.01 (interquartile range, -2.39 to 0.52). After a median follow-up period of 7.4 years (interquartile range, 6.8-8.2 y), the eGFR decreased from a median of 49.4 mL/min per 1.73 m² at baseline to 29.4 mL/min per 1.73 m², an annual eGFR percentage decrease of -4.68%. Lower RPA z-scores were correlated weakly with a higher annual decrease in eGFR (Spearman correlation, 0.35; 95% confidence interval, -0.25 to 0.76). This pilot study shows the feasibility of obtaining RPA from a routine ultrasound and suggests that a lower baseline RPA may be associated with a greater decrease in eGFR over time. Further studies with larger patient cohorts are needed to confirm this association.

Outcomes of solitary functioning kidneys-renal agenesis is different than multicystic dysplastic kidney disease

BACKGROUND

Multicystic dysplastic kidney (MCDK) disease and unilateral renal agenesis (URA) are well-known causes of a solitary functioning kidney (SFK) and are associated with long-term kidney injury. The aims of this study were to characterize the natural history of SFK at our center, define the risk factors associated with chronic kidney injury, and identify distinguishing features between URA and MCDK that predict outcome.

METHODS

This was a retrospective cohort study of 230 SFK patients. We compared MCDK (n=160) and URA (n=70) according to clinical features at diagnosis and kidney outcomes over follow-up. Univariate and multivariate binary regression analysis was used to determine independent risk factors for chronic kidney injury, defined as the composite outcome of hypertension, proteinuria, or chronic kidney disease (eGFR <60 mL/min/1.73m²).

RESULTS

URA had a higher prevalence of comorbid genetic syndromes (15 vs. 6%, p=0.04), non-renal anomalies (39 vs. 11%, p<0.001), and congenital anomalies of the kidney and urinary tract (CAKUT) (51 vs. 26%, p<0.001) than MCDK. Over follow-up, URA experienced more hypertension (19 vs. 3%, p=0.002), proteinuria (12 vs. 3%, p=0.03), and the composite outcome (19 vs. 6%, p=0.003) than MCDK. Independent risk factors for chronic kidney injury included CAKUT (OR 5.01, p=0.002) and URA (OR 2.71, p=0.04).

CONCLUSIONS

In our population, URA was more likely to have associated syndromes or anomalies, and to have worse outcomes over time than MCDK. URA diagnosis was an independent risk factor for chronic kidney injury. Our results will be used to develop a standardized clinical pathway for SFK management. A higher resolution version of the Graphical abstract is available as Supplementary information.

The old becomes new: advances in imaging techniques to assess nephron mass in children

Renal imaging is widely used in the assessment of surrogate markers of nephron mass correlated to renal function. Autopsy studies have tested the validity of various imaging modalities in accurately estimating "true" nephron mass. However, in vivo assessment of nephron mass has been largely limited to kidney volume determination by ultrasonography (US) in pediatric populations. Practical limitations and risks create challenges in incorporating more precise 3D volumetric imaging, like magnetic resonance imaging (MRI), and computed tomography (CT) technologies, compared to US for routine kidney volume assessment in children. Additionally, accounting for structural anomalies such as hydronephrosis when estimating renal parenchymal area in congenital anomalies of the kidney and urinary tract (CAKUT) is important, as it correlates with chronic kidney disease (CKD) progression. 3D imaging using CT and MRI has been shown to be superior to US, which has traditionally relied on 2D measurements to estimate kidney volume using the ellipsoid calculation. Recent innovations using 3D and contrast-enhanced US (CEUS) provide improved accuracy with low risk. Indexing kidney volume to body surface area in children is an important standard that may allow early detection of CKD progression in high-risk populations. This review highlights current understanding of various imaging modalities in assessing nephron mass, discusses applications and limitations, and describes recent advances in the field of imaging and kidney disease. Although renal imaging has been a long-standing, essential tool in assessing kidney disease, innovation and new applications of established technologies provide important tools in the study and management of kidney disease in children.

Multi-instance Deep Learning of Ultrasound Imaging Data for Pattern Classification of Congenital Abnormalities of the Kidney and Urinary Tract in Children

OBJECTIVE

To reliably and quickly diagnose children with posterior urethral valves (PUV), we developed a multi-instance deep learning method to automate image analysis.

METHODS

We built a robust pattern classifier to distinguish 86 children with PUV from 71 children with mild unilateral hydronephrosis based on ultrasound images (3504 in sagittal view and 2558 in transverse view) obtained during routine clinical care.

RESULTS

The multi-instance deep learning classifier performed better than classifiers built on either single sagittal images or single transverse images. Particularly, the deep learning classifiers built on single images in the sagittal view and single images in the transverse view obtained area under the receiver operating characteristic curve (AUC) values of 0.796 ± 0.064 and 0.815 ± 0.071, respectively. AUC values of the multi-instance deep learning classifiers built on images in the sagittal and transverse views with mean pooling operation were 0.949 ± 0.035 and 0.954 ± 0.033, respectively. The multi-instance deep learning classifiers built on images in both the sagittal and transverse views with a mean pooling operation obtained an AUC of 0.961 ± 0.026 with a classification rate of 0.925 ± 0.060, specificity of 0.986 ± 0.032, and sensitivity of 0.873 ± 0.120, respectively. Discriminative regions of the kidney located using classification activation mapping demonstrated that the deep learning techniques could identify meaningful anatomical features from ultrasound images.

CONCLUSION

The multi-instance deep learning method provides an automatic and accurate means to extract informative features from ultrasound images and discriminate infants with PUV from male children with unilateral hydronephrosis.

Clinical predictors of chronic kidney disease in congenital lower urinary tract obstruction

Congenital lower urinary tract obstruction is associated with oligohydramnios and significant perinatal mortality and long-term chronic kidney disease. The counseling of families facing this diagnosis, especially when prenatal intervention is proposed, is fraught with ambiguity. This review aims to equip the provider with the current evidence behind the conventional and novel biomarkers predictive of chronic kidney disease. The relevant clinical predictors are categorized by when they are identified, antenatally or postnatally, and as either anatomic or chemical. They are considered for their prognostic value and the challenges in obtaining them, specifically the risk to the fetus in the case of prenatal biomarkers. Serum creatinine in infancy is the traditional chemical biomarker of kidney function and continues to be a consistent predictor of future serum creatinine. β-2 microglobulin may provide earlier information regarding fetal glomerular and tubular function and is also predictive of long-term serum creatinine. Renal parenchymal area is an anatomic surrogate of nephron mass that is used in both prenatal and postnatal settings. Understanding the anatomic and chemical biomarkers is essential for future refinement of the staging algorithm used to distinguish which patients may benefit from early in utero intervention.

Best ultrasound parameter for prediction of adverse renal function outcome after pyeloplasty

OBJECTIVE

To evaluate the clinical value of preoperative ultrasound parameters for post-pyeloplasty outcomes in pediatric patients with ureteropelvic junction obstruction.

METHODS

The medical records of 187 pediatric and adolescent patients who underwent pyeloplasty as a result of ureteropelvic junction obstruction between 2010 and 2016 were retrospectively reviewed. The severity of hydronephrosis was measured by the Society for Fetal Urology grade, anteroposterior pelvic diameter, urinary tract dilation, hydronephrosis index, and the hydronephrosis area to renal parenchyma ratio at 3, 6 and 12 months. Adverse renal function outcome was defined as ≥10% decrease in postoperative differential renal function compared with preoperative values.

RESULTS

Of the 187 patients, preoperative hydronephrosis was categorized as Society for Fetal Urology grade 3 in 26 patients (13.9%) and grade 4 in 161 patients (86.1%). No surgical failures, defined as requirement of repeat surgery or deterioration of hydronephrosis grade, were noted. The mean changes in Society for Fetal Urology grade, anteroposterior pelvic diameter, urinary tract dilation and hydronephrosis area to renal parenchyma ratio showed similar trends of recovery during the follow-up period. In total, 19 patients (10.2%) showed >10% decrease in differential renal function during follow up (mean 42 months). Multivariate logistic regression analysis showed that the hydronephrosis area-to-renal parenchyma ratio was the only significant prognostic factor for adverse renal function outcome (hazard ratio 1.806, 95% confidence interval 1.210-2.859, P = 0.005). Receiver operating characteristic analysis showed that the hydronephrosis area-to-renal parenchyma ratio was the most significant predictive value (area under the curve 0.711, 95% confidence interval 0.618-0.804, P = 0.006).

CONCLUSIONS

Pediatric patients with high hydronephrosis area-to-renal parenchyma ratio values before surgery are more likely to show renal function decline after pyeloplasty.

Is there a need for endoscopic evaluation in symptomatic boys with an unsuspicious urethra on VCUG? A consideration of secondary radiologic signs of posterior urethral valves

INTRODUCTION

A significant proportion of PUV becomes symptomatic after the perinatal period. Voiding cystourethrography (VCUG) often fails to identify PUVs. This study evaluates the relationship between the radiological appearance of the posterior urethra, potential secondary radiological signs and endoscopically documented PUV in boys with febrile UTIs, VUR, refractory symptoms of bladder overactivity or suggestive sonography findings.

PATIENTS AND METHODS

Data on VCUG findings and endoscopy from 92 boys (mean age 27 months) who underwent endoscopic PUV incision between 2012 and 2017 following a VCUG were reviewed. 24 boys with endoscopically unsuspicious urethras were included as control group (mean age 27.5 months). Statistical analysis was performed using Fisher's exact test.

RESULTS

In patients with PUV, the urethra was suspicious on a preoperative VCUG in 45.7%, whereas it appeared normal in 54.3%. Abortive forms of PUV were more frequently found in patients with a radiologically unsuspicious urethra (30%vs.16.7%, p = 0.15). Bladder neck hypertrophy on VCUG (16.7%vs.60.9%, OR 7.5, p < 0.001), a trabeculated bladder on VCUG (72%vs.37.5%, OR 4.3, p < 0.001) and a hypertrophied musculus interuretericus (38%vs.4.2%, OR 11.7, p < 0.001) were more common in patients with PUV and urethras appearing normal on VCUG as compared to controls.

CONCLUSION

Unsuspicious findings of the urethra on VCUG cannot exclude a relevant PUV and implicate a risk of disregarding abortive forms. The presence of secondary radiologic signs of infravesical obstruction on a VCUG despite an unsuspicious posterior urethra in boys with recurrent UTI's as well as refractory symptoms of bladder overactivity or suggestive signs on sonography must be further clarified endoscopically.

Automatic kidney segmentation in ultrasound images using subsequent boundary distance regression and pixelwise classification networks

It remains challenging to automatically segment kidneys in clinical ultrasound (US) images due to the kidneys' varied shapes and image intensity distributions, although semi-automatic methods have achieved promising performance. In this study, we propose subsequent boundary distance regression and pixel classification networks to segment the kidneys automatically. Particularly, we first use deep neural networks pre-trained for classification of natural images to extract high-level image features from US images. These features are used as input to learn kidney boundary distance maps using a boundary distance regression network and the predicted boundary distance maps are classified as kidney pixels or non-kidney pixels using a pixelwise classification network in an end-to-end learning fashion. We also adopted a data-augmentation method based on kidney shape registration to generate enriched training data from a small number of US images with manually segmented kidney labels. Experimental results have demonstrated that our method could automatically segment the kidney with promising performance, significantly better than deep learning-based pixel classification networks.

Survival and Kidney Outcomes of Children with an Early Diagnosis of Posterior Urethral Valves

BACKGROUND AND OBJECTIVES

Posterior urethral valve is the most common cause of bladder outlet obstruction in infants. We aimed to describe the rate and timing of kidney-related and survival outcomes for children diagnosed with posterior urethral valves in United States children's hospitals using the Pediatric Health Information System database.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This retrospective cohort study included children hospitalized between January 1, 1992 and December 31, 2006, who were in their first year of life, had a diagnosis of congenital urethral stenosis, and underwent endoscopic valve ablation or urinary drainage intervention, or died. Records were searched up to December 31, 2018 for kidney-related mortality, placement of a dialysis catheter, and kidney transplantation. Cox regression analysis was used to identify risk factors, and Kaplan-Meier survival analysis used to determine time-to-event probability. Subgroup survival analysis was performed with outcomes stratified by the strongest identified risk factor.

RESULTS

Included were 685 children hospitalized at a median age of 7 (interquartile range, 1-37) days. Thirty four children (5%) died, over half during their initial hospitalization. Pulmonary hypoplasia was the strongest risk factor for death (hazard ratio, 7.5; 95% confidence interval [95% CI], 3.3 to 17.0). Ten-year survival probability was 94%. Fifty-nine children (9%) underwent one or more dialysis catheter placements. Children with kidney dysplasia had over four-fold risk of dialysis catheter placement (hazard ratio, 4.6; 95% CI, 2.6 to 8.1). Thirty-six (7%) children underwent kidney transplant at a median age of 3 (interquartile range, 2-8) years. Kidney dysplasia had a nine-fold higher risk of kidney transplant (hazard ratio, 9.5; 95% CI, 4.1 to 22.2).

CONCLUSIONS

Patients in this multicenter cohort with posterior urethral valves had a 5% risk of death, and were most likely to die during their initial hospitalization. Risk of death was higher with a diagnosis of pulmonary hypoplasia. Kidney dysplasia was associated with a higher risk of need for dialysis/transplant.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2019_10_03_CJN04350419.mp3.

Krt5+ urothelial cells are developmental and tissue repair progenitors in the kidney

Congenital urinary tract obstruction (UTO) is the leading cause of chronic kidney disease in children; however, current management strategies do not safeguard against progression to end-stage renal disease, highlighting the need for interventions to limit or reverse obstructive nephropathy. Experimental UTO triggers renal urothelial remodeling that culminates in the redistribution of basal keratin 5-positive (Krt5⁺) renal urothelial cells (RUCs) and the generation of uroplakin-positive (Upk)⁺ RUCs that synthesize a protective apical urothelial plaque. The cellular source of Upk⁺ RUCs is currently unknown, limiting the development of strategies to promote renal urothelial remodeling as a therapeutic approach. In the present study, we traced the origins of adult Upk⁺ RUCs during normal development and in response to UTO. Fate mapping analysis demonstrated that adult Upk⁺ RUCs derive from embryonic and neonatal Krt5⁺ RUCs, whereas Krt5⁺ RUCs lose this progenitor capacity and become lineage restricted by postnatal day 14. However, in response to UTO, postnatal day 14-labeled adult Krt5⁺ RUCs break their lineage restriction and robustly differentiate into Upk⁺ RUCs. Thus, Krt5⁺ RUCs drive renal urothelial formation during normal ontogeny and after UTO by differentiating into Upk⁺ RUCs in a temporally restricted manner.

Study of the renal Parenchymal volume during the human fetal period

Objective:

To evaluate the renal parenchymal area in human fetuses, providing a descriptive analysis on the renal area development by demographic factors during the second gestational trimester.

Material and Methods:

We analyzed 84 fetuses (44 males and 40 females), for a total of 168 renal units evaluated in terms of longitudinal length, superior pole width, inferior pole width and thickness. Renal volume was calculated by ellipsoid formula. After renal pelvis dissection, length and width were evaluated; as pelvis is free of urine, we considered thickness as 1mm. Renal pelvis volume was also calculated by ellipsoid formula. Renal parenchymal area was assessed by excluding the volume of the renal pelvis from the total renal volume. We performed the statistical analysis by simple linear regression assessing the association between the variables analyzed with the fetal age.

Results:

Gestational age ranged from 12 to 23 weeks post conception. Mean renal parenchymal area of the right kidney was 666.22mm³ (45.86 to 2375.35mm³) and for the left kidney was 606.76mm3 (68.63 to 2402.57mm³). No statistical difference was observed between the sides (p-value = 0.3456) or genders (p-value = 0.07429). Linear regression between renal parenchymal volume and gestational age was positive for right kidney (y = 133.74x-1479.94 / r² = 0.4009) and left kidney (y = 149.53x-1761.59 / r² = 0.4591).

Conclusions:

The linear regression analysis indicated that renal parenchymal area correlated significantly and positively with fetal age, weight and crown-rump length with no statistical differences between gender or laterality. These growth curves provide a reference for functional volume of the kidney during fetal period.

Long-term growth in children with posterior urethral valves

BACKGROUND

Posterior urethral valves (PUVs) are one of the leading causes of pediatric chronic kidney disease (CKD). Growth impairment is prevalent in pediatric CKD, and children with PUVs are at high risk for growth retardation.

OBJECTIVE

The objective of this study was to describe growth profiles in PUVs and to identify risk factors for stunting, defined as age-specific height standard deviation score (SDS) below -2.

PATIENTS AND METHODS

Medical records of 65 patients with PUVs and a minimum follow-up of two years were retrospectively reviewed. Chronic kidney disease stage 1-3 was considered mild CKD, whereas CKD stage 4-5 was considered advanced CKD. Age-specific height, weight, and body mass index (BMI) SDS were determined. Seven potential risk factors for stunting, namely timing of diagnosis, renal dysplasia, timing of surgery, requirement of urinary diversion, nadir serum creatinine after surgery, recurrent febrile urinary tract infection (UTI), and severity of CKD, were analyzed.

RESULTS

Median age at diagnosis, at surgery, and at last follow-up was 0.51, 0.75, and 7.53 years, respectively. All patients underwent valve ablation, and 33.8% required urinary diversion. Median nadir serum creatinine after surgery was 0.40 mg/dL and was higher in patients who underwent urinary diversion (P < 0.001). Growth profiles by CKD stage are displayed in Fig. 1. Median height SDS was -0.40 and was lower in patients with advanced CKD (P = 0.03). Stunting was diagnosed in 15.4%. Advanced CKD was an independent risk factor for stunting, with the odds ratio of 12.7. Urinary diversion and nadir creatinine more than 0.80 mg/dL were weakly associated with stunting but not significant. Timing of diagnosis and surgery, unilateral renal dysplasia, and recurrent febrile UTI were not associated with stunting. Median SDS of weight and BMI was -0.64 and -0.19, respectively. Patients who were thin, of normal weight, overweight, and obese comprised 26.2%, 58.5%, 10.8%, and 4.6%, respectively. There was no significant difference of SDS of weight and BMI across CKD stages (Fig. 1).

DISCUSSION

Deterioration in height began early in the course of disease and was worsening in relation to the decline of renal function. The impact of timing of diagnosis or surgery on height was controversial. Patients who underwent urinary diversion had high nadir creatinine and were likely to have severe PUVs. Although patients with severe baseline renal dysfunction may require urinary diversion, nadir serum creatinine and urinary diversion are not associated with stunting. Delaying progression of CKD could maximize linear growth potential in PUVs. A substantial proportion of patients were overweight or obese. Sufficient caloric intakes may be maintained in patients with PUVs.

FULLY-AUTOMATIC SEGMENTATION OF KIDNEYS IN CLINICAL ULTRASOUND IMAGES USING A BOUNDARY DISTANCE REGRESSION NETWORK

It remains challenging to automatically segment kidneys in clinical ultrasound images due to the kidneys' varied shapes and image intensity distributions, although semi-automatic methods have achieved promising performance. In this study, we developed a novel boundary distance regression deep neural network to segment the kidneys, informed by the fact that the kidney boundaries are relatively consistent across images in terms of their appearance. Particularly, we first use deep neural networks pre-trained for classification of natural images to extract high-level image features from ultrasound images, then these feature maps are used as input to learn kidney boundary distance maps using a boundary distance regression network, and finally the predicted boundary distance maps are classified as kidney pixels or non-kidney pixels using a pixel classification network in an end-to-end learning fashion. Experimental results have demonstrated that our method could effectively improve the performance of automatic kidney segmentation, significantly better than deep learning based pixel classification networks.

Posterior urethral valves: comparison of clinical outcomes between postnatal and antenatal cohorts

BACKGROUND

Posterior urethral valves (PUVs) constitute the most common infravesical urinary obstruction in boys and are often accompanied by severe consequences to the lower and upper urinary tract. Currently, about two-thirds of diagnosis of PUVs has been suspected by prenatal ultrasonography findings. The aim of this study was to compare long-term clinical outcomes in two groups of patients with PUVs, with antenatal vs. postnatal diagnosis.

STUDY DESIGN

This was a retrospective cohort study of 173 patients with PUVs systematically followed up in a tertiary center. Median follow-up time was 66.5 months (interquartile range [IQ], 11.4-147.9 months) for those patients who survived neonatal period. Seventy-nine (45.6%) patients were followed up for more than 5 years and 55 (32%) for more than 10 years. For analysis, the cohort was stratified into two groups according to the clinical presentation (prenatal vs. postnatal). The events of interest were urinary tract infection (UTI), surgical interventions, proteinuria, hypertension, chronic kidney disease (CKD), and death. Survival analyses were performed to evaluate time until occurrence of the events.

RESULTS

Sixty-two patients (35.8%) were diagnosed by fetal sonography. Patients of postnatal group presented a higher incidence rate of UTI episodes (6.5, 95% confidence interval [CI], 4.9-8.3) than antenatal group (1.2, 95% CI, 0.4-2.7) (P < 0.001). Thirty-six patients (21%) presented hypertension, and 77 (44.5%) had persistent mild proteinuria. There was no significant difference in the estimated incidence of hypertension (P = 0.28) and proteinuria (P = 0.78) between antenatal and postnatal groups. The cumulative incidence of CKD stage ≥3 was estimated to be about 37% at 10 years of age, and 56% at 18 years of age. By survival analysis, there was no significant difference in the estimated incidence of CKD stage ≥3 (log-rank = 0.32, P = 0.57) and CKD stage 5 (log-rank = 1.08, P = 0.28, Figure) between antenatal and postnatal groups. Of 173 patients included in the analysis, 13 (7.5%) died during follow-up with a median age of 2.6 months (IQ, 15 days-62 months). Survival analyses have not shown any significant difference in the estimated incidence of death between antenatal and postnatal groups (log-rank = 1.38, P = 0.24).

CONCLUSION

The study findings did not corroborate the initial hypothesis that the rates of renal function declining in patients with PUVs would be attenuated by an early diagnosis and intervention after antenatal diagnosis.

Surgical interventions and anesthesia in the 1st year of life for lower urinary tract obstruction

BACKGROUND

Patients with a prenatal diagnosis of lower urinary tract obstruction (LUTO) may undergo prenatal interventions, such as vesicoamniotic shunt (VAS) placement, as a temporary solution for relieving urinary tract obstruction. A recent FDA communication has raised awareness of the potential neurocognitive adverse effects of anesthesia in children. We hypothesized as to whether a prenatal LUTO staging system was predictive of the number of anesthesia events for prenatally diagnosed LUTO patients.

METHODS

We retrospectively reviewed the prenatal and postnatal clinical records for patients with prenatally diagnosed LUTO from 2012 to 2015. Patients were stratified by prenatal VAS status and by LUTO disease severity according to Ruano et al. (Ultrasound Obstet Gynecol. 2016).

RESULTS

31 patients were identified with a prenatal LUTO diagnosis, and postnatal records were available for 21 patients (seven patients in each stage). When combining prenatal and postnatal anesthesia, there was a significant difference in the number of anesthesia encounters by stage (1.6, 3.7, and 6.7 for Stage I, II, and III respectively, p = .034). Upon univariate analysis, higher gestational age (GA) at birth was associated with a decreased number of anesthesia events in the first year (p = .031).

CONCLUSIONS

The majority of infants with prenatally diagnosed LUTO will undergo postnatal procedures with general anesthesia exposure in the first year of life. Patients with higher prenatal LUTO severity experienced a higher number of both prenatal and postnatal anesthesia encounters. In addition, higher GA at birth was associated with fewer anesthesia encounters in the first year.

LEVEL OF EVIDENCE

This is a prognostic study with Level IV evidence.

A clinical predictive model of chronic kidney disease in children with posterior urethral valves

BACKGROUND

Posterior urethral valves (PUVs) are associated with severe consequences to the urinary tract and are a common cause of chronic kidney disease (CKD). The aim of this study was to develop clinical predictive model of CKD in a cohort of patients with PUVs.

METHODS

In this retrospective cohort study, 173 patients with PUVs were systematically followed up at a single tertiary unit. The primary endpoint was CKD ≥ stage 3. Survival analyses were performed by Cox regression proportional hazard models with time-fixed and time-dependent covariables.

RESULTS

Mean follow-up time was 83 months (SD, 70 months). Sixty-five children (37.6%) developed CKD stage ≥ 3. After adjustment by the time-dependent Cox model, baseline creatinine, nadir creatinine, hypertension, and proteinuria remained as predictors of the endpoint. After adjustment by time-fixed model, three variables were predictors of CKD ≥ stage 3: baseline creatinine, nadir creatinine, and proteinuria. The prognostic risk score was divided into three categories: low-risk (69 children, 39.9%), medium-risk (45, 26%), and high-risk (59, 34.1%). The probability of CKD ≥ stage 3 at 10 years age was estimated as 6%, 40%, and 70% for patients assigned to the low-risk, medium-risk, and high-risk groups, respectively (P < 0.001). The main limitation was the preclusion of some relevant variables, especially bladder dysfunction, that might contribute to a more accurate prediction of renal outcome.

CONCLUSION

The model accurately predicts the risk of CKD in PUVs patients. This model could be clinically useful in applying timely intervention and in preventing the impairment of renal function.

Computer-aided diagnosis of congenital abnormalities of the kidney and urinary tract in children based on ultrasound imaging data by integrating texture image features and deep transfer learning image features

INTRODUCTION

Anatomic characteristics of kidneys derived from ultrasound images are potential biomarkers of children with congenital abnormalities of the kidney and urinary tract (CAKUT), but current methods are limited by the lack of automated processes that accurately classify diseased and normal kidneys.

OBJECTIVE

The objective of the study was to evaluate the diagnostic performance of deep transfer learning techniques to classify kidneys of normal children and those with CAKUT.

STUDY DESIGN

A transfer learning method was developed to extract features of kidneys from ultrasound images obtained during routine clinical care of 50 children with CAKUT and 50 controls. To classify diseased and normal kidneys, support vector machine classifiers were built on the extracted features using (1) transfer learning imaging features from a pretrained deep learning model, (2) conventional imaging features, and (3) their combination. These classifiers were compared, and their diagnosis performance was measured using area under the receiver operating characteristic curve (AUC), accuracy, specificity, and sensitivity.

RESULTS

The AUC for classifiers built on the combination features were 0.92, 0.88, and 0.92 for discriminating the left, right, and bilateral abnormal kidney scans from controls with classification rates of 84%, 81%, and 87%; specificity of 84%, 74%, and 88%; and sensitivity of 85%, 88%, and 86%, respectively. These classifiers performed better than classifiers built on either the transfer learning features or the conventional features alone (p < 0.001).

DISCUSSION

The present study validated transfer learning techniques for imaging feature extraction of ultrasound images to build classifiers for distinguishing children with CAKUT from controls. The experiments have demonstrated that the classifiers built on the transfer learning features and conventional image features could distinguish abnormal kidney images from controls with AUCs greater than 0.88, indicating that classification of ultrasound kidney scans has a great potential to aid kidney disease diagnosis. A limitation of the present study is the moderate number of patients that contributed data to the transfer learning approach.

CONCLUSIONS

The combination of transfer learning and conventional imaging features yielded the best classification performance for distinguishing children with CAKUT from controls based on ultrasound images of kidneys.

A Dynamic Graph Cuts Method with Integrated Multiple Feature Maps for Segmenting Kidneys in 2D Ultrasound Images

RATIONALE AND OBJECTIVES

Automatic segmentation of kidneys in ultrasound (US) images remains a challenging task because of high speckle noise, low contrast, and large appearance variations of kidneys in US images. Because texture features may improve the US image segmentation performance, we propose a novel graph cuts method to segment kidney in US images by integrating image intensity information and texture feature maps.

MATERIALS AND METHODS

We develop a new graph cuts-based method to segment kidney US images by integrating original image intensity information and texture feature maps extracted using Gabor filters. To handle large appearance variation within kidney images and improve computational efficiency, we build a graph of image pixels close to kidney boundary instead of building a graph of the whole image. To make the kidney segmentation robust to weak boundaries, we adopt localized regional information to measure similarity between image pixels for computing edge weights to build the graph of image pixels. The localized graph is dynamically updated and the graph cuts-based segmentation iteratively progresses until convergence. Our method has been evaluated based on kidney US images of 85 subjects. The imaging data of 20 randomly selected subjects were used as training data to tune parameters of the image segmentation method, and the remaining data were used as testing data for validation.

RESULTS

Experiment results demonstrated that the proposed method obtained promising segmentation results for bilateral kidneys (average Dice index = 0.9446, average mean distance = 2.2551, average specificity = 0.9971, average accuracy = 0.9919), better than other methods under comparison (P < .05, paired Wilcoxon rank sum tests).

CONCLUSIONS

The proposed method achieved promising performance for segmenting kidneys in two-dimensional US images, better than segmentation methods built on any single channel of image information. This method will facilitate extraction of kidney characteristics that may predict important clinical outcomes such as progression of chronic kidney disease.

Prenatal renal parenchymal area as a predictor of early end-stage renal disease in children with vesicoamniotic shunting for lower urinary tract obstruction

BACKGROUND

Vesicoamniotic shunting (VAS) and other bladder drainage techniques for fetal lower urinary tract obstruction (LUTO) have been proven to ameliorate pulmonary hypoplasia and increase survival in patients with an initial poor prognosis. Currently there are limited prognostic tools available during gestation to evaluate and predict postnatal renal function.

OBJECTIVE

The aim was to describe the prenatal growth of the renal parenchymal area (RPA) in patients with LUTO and determine its application as a predictor of renal function at one year of life.

STUDY DESIGN

The study population comprised a retrospective cohort of all infants who survived the fetal VAS to birth. Renal growth and size were measured using imageJ software to calculate the RPA in sequential prenatal ultrasounds. The parenchymal area was measured from the image of each kidney with the greatest longitudinal length. These measurements were further correlated and analyzed as a predictor of end-stage renal disease (ESRD) within the first year of life.

RESULTS

Etiologies of LUTO in the 15 male fetuses included eight posterior urethral valves, four Eagle-Barrett/prune belly syndrome, two urethral atresia, and one megacystis microcolon intestinal hypoperistalsis syndrome. All patients had patent shunts, in place, at birth. Furthermore, ultrasonographic parameters such as oligohydramnios, keyhole sign, and bladder wall thickness showed no statistical difference between groups. Renal parenchymal growth correlated with postnatal renal function in both the ESRD (r = 0.409, p = 0.018) and the non-ESRD (r = 0.657, p < 0.001) groups. Most notably, RPA during the 3rd trimester predicted ESRD with the best cut-off point determined to be 8 cm² (sensitivity, 0.714; specificity, 0.882; and positive likelihood ratio, 6.071) (Table).

DISCUSSION

Despite definitive VAS for LUTO, postnatal morbidity and mortality remain high, emphasizing the role of renal dysplasia in postnatal renal failure, in spite of urinary diversion. Renal growth statistically differs between groups in the 3rd trimester of gestation; RPA development appears stagnant in patients that developed ESRD within the first year of life. In contrast, patients that did not develop ESRD continued to have renal parenchymal growth in a linear fashion. This suggests that prenatal RPA may be predictive of postnatal ESRD.

CONCLUSIONS

RPA measurement during the prenatal period could play an important role as a non-invasive tool to predict postnatal renal function and to anticipate postnatal clinical interventions.

Predicting and Modifying Risk for Development of Renal Failure in Boys with Posterior Urethral Valves

PURPOSE OF REVIEW

The purpose of this review is to bring the reader up to date on the current risk factors for the development of renal deterioration in the boys with posterior urethral valves (PUV) and approaches to modify this risk.

RECENT FINDINGS

Renal bladder ultrasound (RBUS) is routinely performed in boys with PUV and recent advancements allow imaging processing that can more accurately quantify renal parenchyma and correlate this with risk for renal loss. Refinement of urine studies may improve our ability to stratify patients into renal loss categories. Use of videourodynamics (VUDS) allows refined assessment of the valve bladder to identify those who might benefit from secondary procedures and/or the addition of targeted pharmacotherapy to improve bladder emptying or dangerous storage pressures. All boys with a history of PUV are at a significant long-term risk of renal deterioration. The literature suggests that several technical advances have improved our ability to predict this risk, although there needs to be further refinement and validation before widespread use. Utilization of close follow-up, VUDS, pharmacotherapy, and bladder drainage provide the best methods to improve care to this group of patients and if more studies confirm their utility, adoption of these as part of standard of care protocols may be warranted.

Parents Refusing Dialysis for a 3-Month-Old With Renal Failure

A 3-month-old boy with failure to thrive was referred to a nephrology clinic after a diagnostic workup for failure to thrive revealed a serum urea nitrogen level of 95 mg/dL and creatinine level of 3.6 mg/dL. A renal ultrasound revealed marked bilateral hydronephrosis with little remaining renal cortex in either kidney. A voiding cystourethrogram revealed evidence of posterior urethral valves. The child had no evident comorbidities. Fulguration of the valves was successfully performed but did not lead to improvement in kidney function. The nephrologists recommended the initiation of dialysis with the hope that the child would be able to receive a kidney transplant in the future. After careful consideration, the family stated that they did not want this child to suffer with a lifetime of dialysis and transplant care. They were also concerned about the impact of this child's illness on their other 2 children and their family. They requested that their son be provided with palliative care only. Experts in nephrology, bioethics, and critical care discuss the ethical issues raised by this parental request.

Impact of Adjuvant Urinary Diversion versus Valve Ablation Alone on Progression from Chronic to End Stage Renal Disease in Posterior Urethral Valves: A Single Institution 15-Year Time-to-Event Analysis

PURPOSE

Long-term progression to end stage renal disease of valve ablation alone vs ablation followed by additional urinary diversion were compared among children with stage 3 chronic kidney disease due to posterior urethral valves.

MATERIALS AND METHODS

We performed a retrospective study of children with posterior urethral valves and stage 3 chronic kidney disease treated at a single institution between 1986 and 2011. The 3 treatment groups were classified as group 1-valve ablation alone, group 2-ablation plus subsequent vesicostomy and group 3-ablation followed by ureterostomies and/or pyelostomies. Baseline demographic characteristics were analyzed. Statistical analyses compared the incidence of time to end stage renal disease among the intervention groups using the Fisher-Freeman-Halton exact test and Kaplan-Meier analysis with the log rank test. Cox regression was used to determine predictors of end stage renal disease progression.

RESULTS

A total of 40 eligible patients were included in the study (group 1-14 patients, group 2-13 patients, group 3-13 patients). Baseline characteristics and post-intervention estimated glomerular filtration rate revealed no significant between-group differences. A statistically significant difference in progression to end stage renal disease was noted within 1 year after diagnosis of stage 3 chronic kidney disease among the treatment groups (log rank test p=0.02). However, cumulative end stage renal disease incidence at 15-year followup showed no statistical difference (log rank test p=0.628). Cox regression analysis determined that bilateral renal dysplasia (HR 2.76, 95% CI 1.21-6.30) and estimated glomerular filtration rate 60 ml/minute/1.73 m² or greater after intervention (HR 0.23, 95% CI 0.09-0.61) were predictive of the likelihood of progression to end stage renal disease.

CONCLUSIONS

Urinary diversion following valve ablation in children with stage 3 chronic kidney disease associated with posterior urethral valves may temporarily delay progression to end stage renal disease. However, no long-term benefit was noted from diversion in the ultimate incidence of end stage renal disease, suggesting that these interventions should be seen as a temporizing measure. Bilateral renal dysplasia and post-intervention estimated glomerular filtration rate are independent variables predicting overall chronic kidney disease progression.

Renal development in the fetus and premature infant

Congenital abnormalities of the kidney and urinary tract (CAKUT) are one of the leading congenital defects to be identified on prenatal ultrasound. CAKUT represent a broad spectrum of abnormalities, from transient hydronephrosis to severe bilateral renal agenesis. CAKUT are a major contributor to chronic and end stage kidney disease (CKD/ESKD) in children. Prenatal imaging is useful to identify CAKUT, but will not detect all defects. Both genetic abnormalities and the fetal environment contribute to CAKUT. Monogenic gene mutations identified in human CAKUT have advanced our understanding of molecular mechanisms of renal development. Low nephron number and solitary kidneys are associated with increased risk of adult onset CKD and ESKD. Premature and low birth weight infants represent a high risk population for low nephron number. Additional research is needed to identify biomarkers and appropriate follow-up of premature and low birth weight infants into adulthood.

Parenchyma-to-hydronephrosis Area Ratio Is a Promising Outcome Measure to Quantify Upper Tract Changes in Infants With High-grade Prenatal Hydronephrosis

OBJECTIVE

To explore the value of renal parenchyma-to-hydronephrosis area ratio (PHAR) in detecting trends of hydronephrosis (HN) improvement or worsening and response to surgical intervention.

METHODS

Initial and follow-up sagittal renal ultrasound images of patients entered into a prenatal HN database from 2008 to 2016, with baseline Society for Fetal Urology (SFU) grades III and IV HN and without vesicoureteral reflux, were evaluated using National Institutes of Health-sponsored image-processing software. Renal parenchymal area, hydronephrosis area (HA), PHAR, anteroposterior diameter (APd), and SFU grade were captured at baseline and most recent visit. Data were analyzed based on the need for surgical intervention to address obstruction.

RESULTS

Out of 193 infants (159 boys; 135 left side), 58 (30%) underwent surgery. Patients managed surgically compared with those managed nonsurgically had worse baseline HN severity markers: SFU grade (3.6 ± 0.5 vs 3.1 ± 0.4; P <.001), urinary tract dilation classification (2.7 ± 0.5 vs 2.2 ± 0.4; P <.001), APd (20.3 ± 10.1 vs 12.8 ± 8.0; P <.001), HA (10.0 ± 6.6 vs 4.7 ± 2.8; P <.001), and PHAR (1.3 ± 1.0 vs 3.0 ± 2.9; P <.001); but both patient groups had similar renal parenchymal area (9.4 ± 3.5 vs 9.7 ± 2.8; P = .5). At last follow-up, the following discrepancies persisted: SFU grade (2.3 ± 1.0 vs 1.7 ± 1.0; P <.001), urinary tract dilation classification (1.5 ± 0.7 vs 1.0 ± 0.7; P <.001), APd (11.7 ± 8.0 vs 7.7 ± 5.7; P <.001), and HA (6.4 ± 5.1 vs 3.6 ± 2.7; P <.001); however, PHAR was equalized for both groups (7.2 ± 14.0 vs 7.1 ± 6.1; P = .9).

CONCLUSION

By concurrently considering changes in renal parenchyma and degree of HN, we found that PHAR appears to be a promising parameter that reflects similarities between patients managed surgically and those managed nonsurgically, despite initial discrepancies. Our data suggest that this variable may provide reassurance and a more objective assessment of improvement after surgery compared with other traditional ultrasound outcome measures.

Prognostic factors and biomarkers of congenital obstructive nephropathy

Congenital obstructive nephropathy (CON) is the leading cause of chronic kidney disease (CKD) in children. Anomalies of the urinary tract are often associated with abnormal nephrogenesis, which is compounded by obstructive injury and by maternal risk factors associated with low birth weight. Currently available fetal and postnatal imaging and analytes of amniotic fluid, urine, or blood lack predictive value. For ureteropelvic junction obstruction, biomarkers are needed for optimal timing of pyeloplasty; for posterior urethral valves, biomarkers of long-term prognosis and CKD are needed. The initial nephron number may be a major determinant of progression of CKD, and most patients with CON who progress to renal failure reach this point in adulthood, presumably compounded by episodes of acute kidney injury. Biomarkers of tubular injury may be of particular value in predicting the need for surgical intervention or in tracking progression of CKD, and must be adjusted for patient age. Discovery of new biomarkers may depend on "unbiased" proteomics, whereby patterns of urinary peptide fragments from patients with CON are analyzed in comparison to controls. Most promising are the analysis of urinary exosomes (restricting biomarkers to relevant tubular cells) and quantitative magnetic resonance imaging techniques allowing precise determination of nephron number and tubular mass. The greatest need is for large prospective multicenter studies with centralized biomarker sample repositories to follow patients with CON from fetal life through adulthood.

Predicting Risk of Chronic Kidney Disease in Infants and Young Children at Diagnosis of Posterior Urethral Valves: Initial Ultrasound Kidney Characteristics and Validation of Parenchymal Area as Forecasters of Renal Reserve

PURPOSE

There is paucity of validated objective early imaging markers to help predict future renal deterioration in infants with posterior urethral valves. We evaluated the prognostic value of total renal parenchymal area, renal echogenicity and corticomedullary differentiation regarding future development of chronic kidney disease.

MATERIALS AND METHODS

We analyzed initial postnatal ultrasonographic images from serial posterior urethral valve cases seen at a single tertiary referral center using National Institutes of Health sponsored image processing software. Echogenicity and corticomedullary differentiation were objectively measured as ratios relative to the adjacent liver or spleen and between cortex and medulla. The primary study outcome, renal function at last followup, was dichotomized based on glomerular filtration rate and/or need for renal replacement therapy (dialysis or renal transplantation, stage 5 chronic kidney disease).

RESULTS

A total of 75 patients were evaluated, of whom 16 had progression to stage 5 chronic kidney disease after a mean ± SD followup of 64.2 ± 38.9 months. Mean renal parenchymal area was 21.41 cm(2) in patients without and 16 cm(2) in patients with stage 5 chronic kidney disease (p <0.001), and mean corticomedullary differentiation was 1.77 and 1.21, respectively (p <0.001). Bilateral echogenic kidneys were significantly associated with development of stage 5 chronic kidney disease (p = 0.004). The performance of corticomedullary differentiation in predicting stage 5 chronic kidney disease was statistically significant (AUROC 0.881, 95% CI 0.776-0.987, p <0.001).

CONCLUSIONS

Estimates of renal parenchyma quantity (total renal parenchymal area) and quality (corticomedullary differentiation and renal echogenicity) measured on initial postnatal ultrasound carry prognostic value in determining future risk of stage 5 chronic kidney disease in patients with posterior urethral valves. These data are promising for developing tools to risk stratify patients, counsel parents and customize monitoring protocols.

Renal Parenchymal Area Growth Curves for Children 0 to 10 Months Old

PURPOSE

Low renal parenchymal area, which is the gross area of the kidney in maximal longitudinal length minus the area of the collecting system, has been associated with increased risk of end stage renal disease during childhood in boys with posterior urethral valves. To our knowledge normal values do not exist. We aimed to increase the clinical usefulness of this measure by defining normal renal parenchymal area during infancy.

MATERIALS AND METHODS

In a cross-sectional study of children with prenatally detected mild unilateral hydronephrosis who were evaluated between 2000 and 2012 we measured the renal parenchymal area of normal kidney(s) opposite the kidney with mild hydronephrosis. Measurement was done with ultrasound from birth to post-gestational age 10 months. We used the LMS method to construct unilateral, bilateral, side and gender stratified normalized centile curves. We determined the z-score and the centile of a total renal parenchymal area of 12.4 cm(2) at post-gestational age 1 to 2 weeks, which has been associated with an increased risk of kidney failure before age 18 years in boys with posterior urethral valves.

RESULTS

A total of 975 normal kidneys of children 0 to 10 months old were used to create renal parenchymal area centile curves. At the 97th centile for unilateral and single stratified curves the estimated margin of error was 4.4% to 8.8%. For bilateral and double stratified curves the estimated margin of error at the 97th centile was 6.6% to 13.2%. Total renal parenchymal area less than 12.4 cm(2) at post-gestational age 1 to 2 weeks had a z-score of -1.96 and fell at the 3rd percentile.

CONCLUSIONS

These normal renal parenchymal area curves may be used to track kidney growth in infants and identify those at risk for chronic kidney disease progression.

Analysis of Kidney Ultrasound Dimensions by Body Habitus and Position

PURPOSE

Renal dimensions are an important assessment of the genitourinary tract used to evaluate critical aspects of renal growth and development. Understanding the effect of patient position is important to use and interpret these parameters. In this prospective study we determined the effect of patient position and general body habitus on renal length and parenchymal area in children undergoing renal ultrasound.

MATERIALS AND METHODS

Between October 2010 and January 2011 children underwent renal ultrasound while prone and supine. Bilateral renal length and renal parenchymal area were measured. Pearson and Bland-Altman statistical analyses were used to examine correlations, measurement bias and the degree of agreement between methods.

RESULTS

Renal length measurements in both positions were complete for 201 right and 196 left kidneys. Parenchymal area measurements were complete for both kidneys in 177 children. When compared individually, supine and prone measures of renal length and parenchymal area highly correlated on Pearson analysis (greater than 0.96 and greater than 0.89, respectively). When compared by method, Bland-Altman analyses of differences vs means showed greater than 50% variance, representing wide limits of agreement with poor interrelation. Neither persistent systematic bias nor body habitus influenced results.

CONCLUSIONS

While Pearson analysis showed high correlation for supine and prone renal measurements, Bland-Altman analysis of renal length and parenchymal area demonstrated wide limits of agreement, not allowing interchangeable use of prone and supine measurements. As such, renal ultrasound should specify standardized positions and benchmarks. These results provide guidance to standardize renal ultrasound measurements when renal size is used as an indicator of kidney health.

Voiding Dysfunction: What Can Radiologists Tell Patients and Pediatric Urologists?

OBJECTIVE

Imaging children with dysfunctional voiding remains a challenge because 98% of these children have normal anatomy. Identifying the 1-2% of children who do have an anatomic basis for incontinence is important; this article focuses on how pediatric urologists use imaging for the evaluation of patients with this condition.

CONCLUSION

Imaging a patient with dysfunctional voiding can provide findings that will allow an accurate diagnosis and lead to optimal management. The key for the pediatric urologist is using imaging studies judiciously because the diagnostic yield is low. If every patient with dysfunctional voiding who presents to the clinic undergoes imaging, there will be little gain. Understanding in which patients to try imaging sooner versus trying medical and behavioral management first is a function of experience.

Developmental Genetics and Congenital Anomalies of the Kidney and Urinary Tract

Congenital anomalies of the kidney and urinary tract (CAKUT) are common birth defects and the leading cause of end-stage renal disease in children. There is a wide spectrum of renal abnormalities, from mild hydronephrosis to more severe cases, such as bilateral renal dysplasia. The etiology of the majority of cases of CAKUT remains unknown, but there is increasing evidence that genomic imbalance contributes to the pathogenesis of CAKUT. Advances in human and mouse genetics have contributed to increased understanding of the pathophysiology of CAKUT. Mutations in genes involved in both transcription factors and signal transduction pathways involved in renal development are associated with CAKUT. Large cohort studies suggest that copy number variants, genomic, or de novo mutations may explain up to one-third of all cases of CAKUT. One of the major challenges to the use of genetic information in the clinical setting remains the lack of strict genotype-phenotype correlation. However, identifying genetic causes of CAKUT may lead to improved diagnosis of extrarenal complications. With the advent of decreasing costs for whole genome and exome sequencing, future studies focused on genotype-phenotype correlations, gene modifiers, and animal models of gene mutations will be needed to translate genetic advances into improved clinical care.

The impact of small kidneys

BACKGROUND

Small kidneys due to renal hypodysplasia (RHD) result from a decrease in nephron number. The objectives of this study were to identify clinical variables that determine long-term renal outcome in children with RHD and to define the role of kidney size as a predictor of developing end-stage renal disease (ESRD).

METHODS

This was a single-center retrospective cohort analysis. The primary outcome was development of ESRD. We identified 202 RHD cases, with 25 (12%) reaching ESRD at mean age of 8.9 (±6.6) years.

RESULTS

Children with RHD with a known genetic syndrome had the smallest kidneys while those with posterior urethral valves (PUV) had the largest kidneys at diagnosis. Cases with bilateral RHD were most likely to develop ESRD. Younger gestational age (OR 0.8, CI 0.69-0.99, p = 0.05), smaller kidney size at diagnosis (OR 0.13, CI 0.03-0.47, p = 0.002), lower best-estimated glomerular filtration rate (eGFR) (OR 0.74, CI 0.58-0.93, p = 0.01), proteinuria (OR 1.03, CI 1.01-1.05, p < 0.001) and high blood pressure (OR 1.02, CI 1.01-1.04, p = 0.01) were associated with development of ESRD, while kidney size at diagnosis was independently associated with ESRD (HR 0.03, CI 0.01-0.72, p = 0.043).

CONCLUSIONS

In children with RHD, kidney size at diagnosis predicts the likelihood of developing ESRD.

Congenital urinary tract obstruction: the long view

Maldevelopment of the collecting system resulting in urinary tract obstruction (UTO) is the leading identifiable cause of CKD in children. Specific etiologies are unknown; most cases are suspected by discovering hydronephrosis on prenatal ultrasonography. Congenital UTO can reduce nephron number and cause bladder dysfunction, which contribute to ongoing injury. Severe UTO can impair kidney growth in utero, and animal models of unilateral ureteral obstruction show that ischemia and oxidative stress cause proximal tubular cell death, with later development of interstitial fibrosis. Congenital obstructive nephropathy, therefore, results from combined developmental and obstructive kidney injury. Because of inadequacy of available biomarkers, criteria for surgical correction of upper tract obstruction are poorly established. Lower tract obstruction requires fetal or immediate postnatal intervention, and the rate of progression of CKD is highly variable. New biomarkers based on proteomics and determination of glomerular number by magnetic resonance imaging should improve future care. Angiotensin inhibitors have not been effective in slowing progression, although avoidance of nephrotoxins and timely treatment of hypertension are important. Because congenital UTO begins in fetal life, smooth transfer of care from perinatologist to pediatric and adult urology and nephrology teams should optimize quality of life and ultimate outcomes for these patients.

The Fate of Nephrons in Congenital Obstructive Nephropathy: Adult Recovery is Limited by Nephron Number Despite Early Release of Obstruction

PURPOSE

Urinary tract obstruction and reduced nephron number often occur together as a result of maldevelopment of the kidneys and the urinary tract. We determined the role of nephron number on adaptation of the remaining nephrons of mice subjected to neonatal partial unilateral ureteral obstruction followed through adulthood.

MATERIALS AND METHODS

Wild-type and Os/+ mice (the latter with 50% fewer nephrons) underwent sham operation or partial unilateral ureteral obstruction in the first 2 days of life. Additional mice underwent release of unilateral ureteral obstruction at 7 days. All kidneys were harvested at 3 weeks (weaning) or 6 weeks (adulthood). Glomerular number and area, glomerulotubular junction integrity, proximal tubular volume fraction and interstitial fibrosis were measured by histomorphometry.

RESULTS

In the obstructed kidney unilateral ureteral obstruction caused additional nephron loss in Os/+ but not in wild-type mice. Glomerular growth from 3 to 6 weeks was impaired by ipsilateral obstruction and not preserved by release in wild-type or Os/+ mice. Proximal tubular growth was impaired and interstitial collagen was increased by ipsilateral obstruction in all mice. These conditions were attenuated by release of unilateral ureteral obstruction in wild-type mice but were not restored in Os/+ mice. Unilateral ureteral obstruction increased interstitial collagen in the contralateral kidney while release of obstruction enhanced tubular growth and reduced interstitial collagen.

CONCLUSIONS

Unilateral ureteral obstruction in early postnatal development impairs adaptation to reduced nephron number and induces additional nephron loss despite release of obstruction. Premature and low birth weight infants with congenital obstructive nephropathy are likely at increased risk for progression of chronic kidney disease.

Segmentation of renal parenchymal area from ultrasound images using level set evolution

This paper presents a framework for segmentation of renal parenchymal area from ultrasound images based on a 2-step level set method. We used distance regularized level set evolution method to partition the kidney boundary, followed by region-scalable fitting energy minimization method to segment the kidney collecting system, and determined renal parenchymal area by subtracting the area of the collecting system from the gross kidney area. The proposed method demonstrated excellent validity and low inter-observer variability.