Introduction
CAKUT refers to congenital anomalies of the kidney and the urinary tract. It is present from birth, and it is due to the abnormal development of the urinary system. It may cause one or more kidney or urinary tract abnormalities. The congenital anomalies of the kidney and the urinary tract are the most common malformations at birth. It may range from mild, symptomatic malformations to life-threatening pathologies.
What Is CAKUT Kidney?
Congenital anomalies of the kidney and the urinary tract (CAKUT) refer to a group of abnormalities that affect the kidneys or the structures of the urinary tract. It can range from mild, asymptomatic malformations like double ureter or minimal ureteral obstruction to severe malformations like bilateral renal agenesis or renal dysplasia. Several congenital abnormalities of the kidneys are a part of the syndrome.
What Are the Causes of CAKUT Kidney?
CAKUT can be caused by a combination of genetic and environmental factors. Variations in PAX2 and HNF1B genes are responsible for CAKUT. Mutations in these genes disrupt the development of the kidneys or the parts of the urinary tract. Mutations in several other genes are associated with the development of isolated or syndromic CAKUT. Most of the congenital anomalies of the kidney and the urinary tract are autosomal dominant disorders. CAKUT is the most common reason for end-stage renal disease in children.
How Is CAKUT Kidney Classified?
CAKUT includes duplex kidney, ureteropelvic junction obstruction, horseshoe kidneys, renal dysplasia, renal hypodysplasia or agenesis, hydronephrosis, megaureter, vesicoureteral reflux, posterior urethral valve.
CAKUT is also associated with syndromes, including Prune Belly syndrome, Meckel-Gruber syndrome, Joubert syndrome, short rib syndrome, Bardet-Biedl syndrome, Zellweger syndrome, trisomies and congenital anomalies of the kidneys, VACTER-L association, Potter syndrome, caudal dysplasia syndrome, sirenomelia, autosomal dominant polycystic kidneys, and autosomal recessive polycystic kidneys.
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Duplex Kidney - Duplex kidney refers to the double ureter or ureteral duplication. Ureteral duplication can be complete or incomplete. Incomplete ureteral duplication is also called bifid collecting systems. If two separate pyelocalyceal systems are present and they join at the ureteropelvic junction, it is known as the bifid pelvis. If two separate ureters enter the bladder, it is called complete ureteral duplication. It is associated with complications like obstruction, reflux, and infection. Ureteral duplication can also be associated with other renal dysplasia or Wilms’ tumor. A laparoscopic polar nephrectomy with ureteropyeloanastomosis is performed to treat this condition.
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Ureteropelvic Junction Obstruction - It is the most common cause of antenatal hydronephrosis. Various factors, such as insertion anomalies of the ureters, ureteral muscular hypertrophy, peripelvicalyceal fibrosis, and abnormal blood vessels that cross over the ureter or renal pelvis, can cause ureteropelvic junction obstruction or stenosis. Chronic obstruction can result in hydronephrosis (excess fluid in the kidney), pyelonephritis (bacterial infection which causes kidney inflammation), and renal failure.
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Horseshoe Kidney or Renal Fusion - Most of the cases show fusion at the lower pole of the kidneys. It is associated with a narrow pelvis, and in some cases, it is associated with ureteropelvic junction obstruction, and children may present with urinary tract infections, hematuria, and abdominal mass. Transperitoneal laparoscopic pyeloplasty helps detect the crossing vessels in horseshoe kidneys.
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Posterior Urethral Valves - These are the common cause of lower urinary tract obstruction in male infants and fetuses. It refers to the development of an obstructive membrane in the urethra. This will result in oligohydramnios (decreased amniotic fluid volume). The affected fetuses present with a massively distended abdomen, which is due to megacystitis. The urinary bladder drains by vesico-amniotic shunt in utero or by vesicocentesis after birth. The abdomen shrinks and acquires the appearance of a prune. Hence, it is named prune-belly syndrome.
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Renal Dysplasia - Renal dysplasia is a condition in which the internal structures of the kidneys show abnormal development in the womb, and it can be obstructive or nonobstructive. Obstructive renal dysplasia can cause distension of the urinary bladder. Nonobstructive renal dysplasia can be syndromic and nonsyndromic.
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Renal Hypodysplasia - Renal hypodysplasia or aplasia is characterized by the presence of abnormally small and malformed kidneys. It belongs to a group of perinatally lethal renal disorders, including bilateral renal aplasia, unilateral renal agenesis with contralateral dysplasia, and severe obstructive uropathy.
The syndromes associated with CAKUT kidneys include the following:
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Meckel-Gruber Syndrome - Meckel syndrome presents with severe renal and central nervous system malformations. It is characterized by the presence of renal cystic dysplasia, occipital encephalocele, cleft lip, cleft palate, oligohydramnios, polydactyly, congenital hepatic fibrosis, and ambiguous genitalia.
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Joubert Syndrome - Joubert syndrome is associated with cystic renal dysplasia and the presence of tubulointerstitial nephritis and cysts at the corticomedullary junction. It is also associated with neurological manifestations.
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Short Rib Syndrome - Short rib syndrome is characterized by short ribs and a narrow thorax, cleft lip, cleft palate, cystic renal dysplasia, hepatic fibrosis, and ocular and cerebral anomalies.
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Bardet-Biedl Syndrome - Bardet-Biedl syndrome is characterized by retinitis pigmentosa, renal dysplasia, obesity, polydactyly, learning disability, and hypogenitalism.
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Zellweger Syndrome - This syndrome is associated with renal cystic dysplasia, horseshoe kidney, fetal lobulations, and urethral duplication.
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Trisomies and Congenital Anomalies of the Kidneys - Trisomies 13, 18, and 21 are associated with hydronephrosis, horseshoe kidney, cortical cysts, and cystic dysplasia, duplex kidney, glomerular microcysts, or renal hypoplasia.
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VACTER-L Association - VACTER-L refers to vertebral anomalies, anal and cardiac malformations, tracheoesophageal fistula or atresia, radial and renal anomalies, and limb malformations.
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Potter Syndrome - Potter syndrome is characterized by the complete absence of both kidneys. The typical facial features associated with Potter’s face are the presence of folds under the eyes, receding chin, flat nose, and low-set ears, as well as pulmonary hypoplasia and rocker-bottom feet.
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Caudal Dysplasia Syndrome - It is associated with renal abnormalities such as bilateral renal agenesis, renal dysplasia, and horseshoe kidney.
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Sirenomelia - Renal abnormalities associated with sirenomelia include bilateral or unilateral renal agenesis with absent ureters and urinary bladder, renal dysplasia, and renal hypoplasia.
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Autosomal Dominant and Recessive Polycystic Kidneys - These abnormalities are associated with multiple cyst formations in the kidneys.
How Are CAKUT Diagnosed?
CAKUT kidney diagnosis is based on ultrasound examination during pregnancy and genetic testing for patients with a familial history of CAKUT.
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Ultrasound Imaging performed during or after the third month of gestation helps in the diagnosis. Postnatally, patients with renal abnormalities can be diagnosed with computed tomography (CT) scans and ultrasounds, and urological tests such as bladder scans, voiding cystourethrogram, lasix renograms, and uroflow.
How Are CAKUT Treated?
Treatment depends on the severity of the condition. Mild forms of the disease can damage the kidneys or other structures due to blockage of urine and requires catheterization to help with the voiding of urine. Surgical correction is performed in some cases. Severe cases can result in end-stage kidney failure and require dialysis or renal transplantation.
Conclusion
Congenital anomalies of the kidney and the urinary tract are a group of disorders that are present from birth due to the abnormal development of the urinary system. It can be diagnosed with ultrasound scans performed during pregnancy. Severe forms of disease require supportive management. However, dialysis or renal transplantation is required for patients with end-stage renal disease.
