Early detection of congenital urinary tract malformations vital
Oluwatoyin F.Bamgbola, M.D., FAAP
Focus on Subspecialties
Congenital anomalies of the kidney and urinary tract (CAKUT) comprise the most common
causes of pediatric end-stage kidney disease. Therefore, early detection and optimal
management are essential for favorable outcomes.
Since there is a 30% association between CAKUT and other nonrenal anomalies, it is
essential that pediatricians also recognize the syndromic or nonsyndromic patterns
of CAKUT (see table) (Hwang DY, et al. Kidney Int.2014;85:1429-1433).
A major advancement that has improved detection and outcomes in CAKUT is universal
antenatal renal ultrasound (RUS) during pregnancy. A greater awareness of the causes
and management of CAKUT anomalies will undoubtedly improve long-term outcomes. The
following example underscores the importance of early detection.
An obstetrician informs you that prenatal renal ultrasonography (RUS) revealed bilateral,
moderate-severe hydronephrosis in a newborn in the nursery. What are the major developmental
factors that will determine the clinical outcome in this child?
Abnormal development of renal parenchyma in CAKUT mayresult in significant renal dysfunction. Common causes include renal agenesis (absence
of one or both kidneys), renal hypodysplasia (RH) (reduced size and abnormal development)
and multicystic-dysplastic kidneys (MCDK) (cysts with abnormal development).
Unlike fatal outcome in MCDK, bilateral RH often presents as maternal oligohydramnios
and may feature as Potter facies, short gut syndrome, limb malformations and lung
hypoplasia. Survival beyond infancy in neonates with bilateral severe renal parenchymal
disease generally is poor, especially if assisted ventilation and dialysis are required
in the neonatal period. Therefore, earlier detection may allow for improved outcomes.
Outcomes for infants with unilateral malformation are better than observed for bilateral
disease. Yet, contralateral anomalies such as vesicoureteral reflux (VUR) also may
occur. While contralateral VUR often is low grade and tends to resolve spontaneously
by 2 years of age, other contralateral anomalies may predispose to the development
of chronic kidney disease. Therefore, routine monitoring by serial RUS may be required,
along with diligent assessment of blood pressure, urine and renal function.
Favorable renal outcomes are more likely in patients who do not have other risk factors
for kidney disease. Although hypertension is infrequent, nephrectomy of unilateral
RH or MCDK may be warranted in the event of severe or intractable hypertension.
A double collecting system is another common CAKUT anomaly that warrants earlier detection for an improved outcome.This anomalymay be complete (two ureters with separate entrance into the bladder) or incomplete
(bifid pelvis or bifid ureters). It is more common in girls and is likely of autosomal
In complete duplication, ureters draining the upper pole may terminate in the bladder
as a ureterocele, resulting in hydronephrosis. Ectopic opening of the ureter into
the urethra may cause urinary incontinence. There is a 20-fold increase in urinary
tract infections (UTIs) in children with ureter duplication.
Ureteropelvic junction obstruction (UPJO) and posterior urethral valve (PUV) are common
causes of congenital hydronephrosis(CH) in newborns. Moderate-severe UPJO may require surgical repair to mitigate or prevent
permanent renal damage.
Predictors of progression of CH on antenatal RUS are high renal pelvic diameter, bilateral
involvement and presence of severe hydronephrosis in a single kidney. In these instances,
urgent postnatal RUS should be performed within 24 hours of life. If hydronephrosis
is persistent, particularly if bilateral, evaluation with voiding cystourethrogram
(VCUG) is required to exclude PUV in male infants.
Bilateral hydronephrosis also may result from abnormalities at the ureterovesical
junction (UVJ). In the absence of VUR, PUV or UVJ obstruction, diuretic renogram (renal
scan to assess drainage and function) is needed to exclude UPJO. Renal ultrasound
should be performed between 2 and 14 days of life in neonates with severe unilateral
hydronephrosis and delayed until 7 days after birth in those with mild-moderate hydronephrosis.
Spontaneous resolution is expected in over 94% of infants with mild-moderate (urinary
tract dilation P1-P2) hydronephrosis by 2 years of age (Mamì C, et al. Pediatr Nephrol.
2009;24:2005-2008; Nguyen HT, et al. J Pediatr Urol. 2014;10:982-998).
Finally, prophylactic antibiotics are recommended for prevention of UTI in infants
with severe hydronephrosis until VCUG excludes VUR (Braga LH, et al. Pediatrics. 2013;131:e251-e261).
In any given patient, including the patient described above, the presence of bilateral,
moderate-to-severe hydronephrosis is a major prognostic factor that will determine
renal development and general outcomes. Immediate assessment of the CAKUT, including
RUS, along with renal scan to assess function, monitoring of renal function by periodic
serum creatinine and urine output, and prompt consultation with urology is warranted
since surgical correction may be required. Earlier intervention and more advanced
imaging techniques may improve the outcome in this newborn.
Dr. Bamgbola is a member of the AAP Section on Nephrology.