Abstract
Background and Aims
Congenital anomalies of the kidney and urinary tract (CAKUT) are the major cause of chronic kidney disease and end-stage kidney disease in childhood. Solitary functioning kidney (SFK) is part of the spectrum of CAKUT. Congenital SFK is mainly due to unilateral renal agenesis (URA) and multi-cystic dysplastic kidney (MCDK). With the implementation of routine fetal ultrasound screening, SFK is increasingly recognized before birth, significantly raising the number of patients referred to paediatric nephrology units for clinical monitoring during childhood.
Understanding the pathophysiology of SFK is pivotal for guiding the clinical management and informing long-term outcome. However, observational studies performed in children with SFK are controversial, especially about the need, methodology and timing of functional assessment. This may be at least in part due to the fact that different models of SFK, including congenital and acquired after unilateral nephrectomy, are often grouped together.
The aim of this study was to assess the clinical, laboratory and functional features of congenital SFK caused by URA and MCDK in children, with a particular focus on the role of renal scintigraphy in estimating kidney function during childhood and adolescence.
Method
We retrospectively collected clinical, laboratory and instrumental records of all consecutive pediatric patients (aged 0-18 years) affected by congenital SFK caused by URA or MCDK referred to the Nephrology and Dialysis Unit of Meyer Children’s Hospital of Florence (Italy) from 1992 to 2019. Patients with unilateral kidney hypodysplasia were excluded. In particular, we reviewed data from ultrasound scanning and sequential renal scintigraphy over time. URA and MCDK were compared for clinical features, long-term course and outcome.
Results
A total of 155 patients with congenital SFK were included in the study and divided in two groups according to the cause of SFK (URA, n=100; MCDK, n=55). The median length of follow-up was 47 and 45 months, respectively. Male sex and ethnicity were equally distributed in the two groups. Prenatal diagnosis was more frequent in MCDK group. We did not observe either preterm birth or low birth weight in patients enrolled. Overall, the clinical features were not statistically different between the two groups. In particular, SFK associated CAKUT, including vesicoureteral reflux, occurred at a comparable frequency. Also, measurement of kidney length by ultrasound scanning, which is often considered suggestive of compensatory hypertrophy, did not differ between groups. Although renal clearance from sequential renal scintigraphy appeared not statistically different between URA and MCDK, the latter seems to reach complete functional adaptation more rapidly and earlier in the first two years of life.
Conclusion
The clinical course and long-term outcome of SFK has been a topic of extensive debate. Due to poor-quality of data (unclear inclusion/exclusion criteria, lack of uniformity in data collection and outcome definition), generalization of findings from observational studies to all patients with SFK could be inappropriate. Congenital SFK could represent the most unbiased group to analyze and this study provides a thorough clinical characterization of a large and strictly selected cohort. Insights from sequential renal scintigraphy suggest a different trend in reaching single kidney complete functional adaptation in URA and MCDK. These results could potentially reveal significant differences in the pathophysiologic mechanisms of reaching compensatory hypertrophy and functional adaptation by the solitary kidney in the two models. Whether confirmed in larger cohorts, these findings could provide important implications for follow-up planning, informing the need, methodology and timing for function assessment, tailoring the clinical management and understanding long-term prognosis.
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