Congenital Anomalies of Kidney and Urinary Tract

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Congenital Anomalies of Kidney and Urinary Tract

Introduction

Human kidney development begins in the fifth week of gestation. Initially, the fetal kidneys are located in the pelvic region but ascend to the thoracolumbar region by the 8th week of gestation. After the 16th week of gestation, urine produced by the kidneys becomes the primary source of amniotic fluid. The kidneys continue to mature until week 32-34 of gestation.

Congenital anomalies of the kidney and urinary tract (CAKUT) encompass a spectrum of structural disorders that arise during the antenatal period. These include:

Kidney agenesis
Kidney hypodysplasia
Multicystic kidney dysplasia (MCDK)
Duplex kidney collecting systems
Pelvic-ureteric junction obstruction (PUJO)
Vesico-ureteric junction obstruction (VUJO)
Megaureter
Posterior urethral valves
Vesicoureteric reflux (VUR)

Causes

The pathogenesis of CAKUT is complex and not fully understood. Currently, over 50 genes have been identified as causing CAKUT, accounting for 12-20% of the disease’s etiology. Other genetic causes, such as structural genomic alterations (i.e. copy number variants) have been detected in 4-11% of patients. Moreover, gene-environment interactions further contribute to the development of CAKUT.

Prevalence

CAKUT is recognized as the most common cause of paediatric chronic kidney disease. The prevalence of CAKUT ranges from 0.3 to 17 per 1,000 liveborn and stillborn infants, and it is frequently detected during the antenatal period, accounting for 20-30% of all congenital anomalies. Upper urinary tract dilatation is the most frequently observed abnormality in cases of CAKUT. While CAKUT typically occurs in isolation, approximately 30% of patients may present with additional non-kidney malformations.

Signs and Symptoms

The severity of CAKUT can vary greatly. Some children might have a mild form and show no symptoms, while others with more severe forms can face life-threatening problems right after birth.

Often, problems in the urinary tract may affect only one kidney and can show up as a mild swelling of one kidney in prenatal ultrasounds. These cases are usually not a cause for concern. However, if both kidneys are affected, it can lead to low levels of amniotic fluid, which can hinder lung development, growth, and the development of muscles and bones.

After the baby is born, how they are affected depends on how well their kidneys are working. They might have issues with urination, stomach pain, struggle to grow, get frequent urinary tract infections, poor kidney function, or develop high blood pressure.

Diagnosis

In diagnosing CAKUT, imaging techniques are essential, with ultrasound often being the first step. Here is how different CAKUT conditions might appear on an ultrasound.

Diagnosis	Ultrasound Findings
Single kidney agenesis	Single kidney: the existing kidney might be larger than normal because it is doing the work of two.
Kidney hypoplasia	Small kidney size, but the kidney tissue itself looks normal on the ultrasound.
Kidney dysplasia	Kidney tissue does not look like it should; the outer layer (cortex) might be thin.
MCDK	Kidney has multiple cysts that do not connect to each other, which means the kidney is not developing normally.
Reflux, PUJO/VUJO	The part of the kidney that collects urine (renal pelvis) or the tubes that carry urine from the kidney to the bladder (ureters) appear wider than normal; PUJO refers to a blockage where the kidney connects to the ureter; and VUJO is a blockage where the ureter connects to the bladder.

Other imaging methods that may be used:

Micturating cystourethrogram (MCUG): Primarily used to diagnose vesicoureteral reflux (VUR) and assess the bladder and urethra, especially in cases of urinary tract infections or suspected posterior urethral valves.
Renal cortical scan (DMSA): This scan uses a radioactive substance and a special camera to assess kidney function, diagnose horseshoe or ectopic kidneys, and see how well the kidneys are working.
MAG3 renogram: Assesses kidney function, urine drainage, and identifies any obstructions.
Computed tomography (CT) / magnetic resonance imaging (MRI): Useful for detailed visualization of complex anatomical issues.

After a thorough examination, doctors might suggest genetic testing for children with CAKUT in the following situations:

Severe CAKUT: The kidney or urinary tract problems are very serious.
Other health issues: If the child has CAKUT along with other health problems, such as, hearing loss or bone / skeletal abnormalities.
Family history: If there is a family history of CAKUT or other kidney diseases.

Management and follow-up care

General

Sometimes, surgery is required to correct blockages in the urinary system or to create a new way for urine to leave the body. This helps with urination and bladder control. If a child has frequent urinary tract infections, they may be given preventative antibiotics to reduce the risk of future infections.

To monitor the long-term health of the kidneys, regular check-ups are essential. These include checking blood pressure, kidney function blood test and urine protein analysis. In addition to medical interventions, adopting a healthy lifestyle is crucial, including drinking enough fluids and avoiding medications or substances that can harm the kidneys.

Special service in HKCH

At HKCH, we believe that complex kidney and urinary tract problems in children require a team approach. We bring together different specialists to provide the best possible care. We carefully review your child’s case, including detailed imaging, to determine if surgery is needed. Our team of paediatric surgeons will perform any necessary operations. We also provide long-term follow-up care to monitor kidney function and address any complications that may arise.

Useful Resources

UK Kidney Association

Acknowledgement

Principal author: Dr Fanny Ho on behalf of Nephrology Team, HKCH

Initial posting: Nov 2025