Congenital anomalies of the kidneys and urinary tract (CAKUT) are one of the most common malformations diagnosed in newborns. 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. 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.
Anomalies of the collecting system
Duplex collecting system: a complete or incomplete duplication of the collecting system (pelvicalyceal system and ureter); has different clinical manifestations depending on the degree of fusion
- The most common congenital anomaly of the urinary tract
- Complete duplication: an additional ureteric bud forms resulting in two separate ureteric buds that interact with the same ; the affected kidney has ; two separate pelvicalyceal systems and two ureters that enter the bladder at different points (double ureter).
- Incomplete duplication: the ureteric bud splits before interacting with the ; the affected kidney has two collecting systems that merge between the ureteropelvic junction and the urinary bladder, resulting in a single ostium in the bladder
- Associated with , , , and
- Ureteroureteral reflux may occur due to Y-shaped ureter.
- Ectopic ureter: The ureter opening is located caudal to the normal insertion site on the bladder.
- Ureterocele: abnormal dilation of the terminal portion of the ureter, which bulges into the urinary bladder or extends to the bladder neck and the urethra; often appears balloon-shaped on cystoscopy
- : See article on “Urinary tract obstruction.”
Malformation of the renal parenchyma
Renal agenesis: the absence of the kidney and the ureter
- ♂ > ♀
- Pathophysiology: ureteric bud does not develop → complete lack of stimulating signals for differentiation of metanephric blastema → kidney fails to develop.
- Unilateral renal agenesis; : usually asymptomatic, depending on the condition of the other kidney (see )
- Bilateral renal agenesis: causes
- Renal hypoplasia: underdevelopment of the kidney characterized by a reduced number of nephrons
Renal dysplasia: abnormal development of the kidney that results in a nonfunctional kidney with abnormal features (e.g., cysts, increased amount of connective tissue)
- Pathophysiology: Ureteric bud does not properly stimulate differentiation of metanephric blastema → disorganized nephrons, reduced number of nephrons, and abnormal cells
- Unilateral dysplasia is usually asymptomatic. (see )
- Bilateral dysplasia leads to early renal insufficiency and if present in utero.
- Examples: , , ,
- Associated with anomalies of the collecting system that predispose to UTI
- Renal aplasia: kidney with only rudimentary renal parenchyma present with no residual function
Congenital solitary kidney
- Definition: the presence of a single functioning kidney due to absence or anomalies of the contralateral kidney
- Often asymptomatic and diagnosed during prenatal ultrasound screening
- A solitary kidney is usually hypertrophic to compensate for the contralateral kidney
- Higher incidence of anomalies (e.g., vesicoureteral reflux)
- Increased risk of hypertension, renal insufficiency, and progression to end-stage renal disease
Anomalies of kidney migration
Horseshoe kidney: Fusion of the left and right inferior renal poles
- Normal ascent interrupted as fused kidney gets caught on the inferior mesenteric artery (IMA).
- Increased incidence in patients with chromosomal aneuploidy (e.g., trisomies 13, 18, 21, and Turner syndrome)
- Usually asymptomatic; typically diagnosed incidentally on abdominal imaging for unrelated conditions
- Rarely requires treatment
- Increased risk of renal cancer, , , infections, and
- Renal dystopia and renal ectopia: displacement of the kidney within the retroperitoneum
- Crossed dystopia: displacement of the kidneys; both kidneys located on the same side of the spine
- Malrotation: Torsion of the orthotopic kidney
- Disturbance of embryonic development
- Environmental factors
- In utero exposure to ACE inhibitors or angiotensin II receptor blockers → juxtaglomerular hyperplasia, absent proximal convoluted tubules, or renal fibrosis
- Most CAKUT are incidental findings with no clinical significance.
- CAKUT are considered clinically significant if they can lead to , , , , or .
- Signs that an underlying clinically significant CAKUT may be present include:
- Ultrasound imaging of the kidneys and bladder
- Voiding cystourethrogram
- 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
- Clinical features
- Conservative: abdominal muscle training and stabilization with abdominal wall binders
- Surgical: laparoscopic nephropexy
The differential diagnoses listed here are not exhaustive.
- The majority of cases do not require treatment.
- If there is vesicoureteral reflux, administer antibiotic prophylaxis (see )
- If there is vesicoureteral reflux with recurrent cystitis or pyelonephritis, perform surgical correction
- Laparoscopic nephrectomy may be indicated in cases with recurrent pyelonephritis and loss of kidney function.