• Clinical science

Congenital anomalies of the kidneys


Congenital anomalies of the kidneys and urinary tract (CAKUT) are one of the most common malformations diagnosed in newborns. Even though most cases are initially asymptomatic, up to 50% of children with end-stage renal disease have an underlying CAKUT. For this reason, early identification of these malformations is essential in order to prevent renal damage. The pathogenesis of CAKUT is multifactorial; both specific genes and environmental factors (e.g., in utero exposure to ACE inhibitors) have been implicated in the development of CAKUT.



Clinical features



  • Ultrasound imaging of the kidneys and bladder
    • First-line imaging modality
    • Detects anatomical abnormalities
    • Renal ultrasound is warranted for all children with recurrent UTIs or UTI in children < 24 months of age.
  • Voiding cystourethrogram
    • Detects retrograde movement of urine from the bladder to the urinary tract
    • Although the test is invasive and involves radiation exposure, it is warranted in patients with recurrent UTIs or single UTI and abnormal findings on renal ultrasound.
  • Intravenous pyelogram: detects anatomic abnormalities; has largely been replaced by ultrasound and CT urography
  • CT scan: detects anatomic abnormalities; can complement renal ultrasound if findings on ultrasound are equivocal


Differential diagnoses

Floating kidney


The differential diagnoses listed here are not exhaustive.



Condition Anomaly Important notes
Duplex kidney
  • Kidney with a duplication of the collection system
Renal agenesis
  • Absence of the kidney
  • >
  • Interdisciplinary treatment in cases of bilateral agenesis
Renal aplasia
  • Incompletely developed or absent kidney
Renal dysplasia
  • Abnormal development of the kidney (see Potter classification)
  • Disorganized nephrons, ↓ number of nephrons, inappropriate differentiation of renal tissue
  • Associated with collecting system anomalies that predispose to UTI
  • Unilateral dysplasia is usually asymptomatic; bilateral dysplasia leads to early renal insufficiency and may lead to renal failure.
Renal hypoplasia
Renal dystopia/renal ectopia
  • Torsion of the orthotopic kidney

Crossed dystopia

Horseshoe kidney
  • Fusion of the left and right inferior renal poles


Condition Anomaly Important notes
Bifid Ureter
  • Possible yo-yo effect of the urine in the Y-shaped ureter (uretero-ureteral reflux)
Double Ureter
  • Duplication of the ureter with two separate orifices merging into the bladder
Bifid collecting system
  • Duplication of the renal pelvis; the two merge directly at the ureteropelvic junction
Ectopic ureter
  • The ureteral opening is located caudal to the normal insertion site on the bladder.
  • Prenatal hydronephrosis
  • Postnatal UTI
  • In females, the ureter may bypass the external sphincter and insert directly in the vagina, resulting in incontinence.
  • Abnormal dilation of the terminal portion of the ureter, which may occur in the bladder or in the urethra