Introduction:
Multicystic dysplastic kidney (MCDK) is a common congenital anomaly affecting the kidneys. It is a severe form of renal dysplasia. It is the second most cause of abdominal mass in children, which gradually shrinks in size and vanishes. More than 50 % of cases of multilocular dysplastic kidneys are diagnosed antenatally. Children may develop hypertension associated with unilateral MCDK and need regular follow-up. Unilateral MCDKs show a good prognosis, while bilateral MCDKs are often fatal.
What Is a Multicystic Dysplastic Kidney?
The multicystic dysplastic kidney is a developmental anomaly of the kidney that is characterized by non-functional renal tissue with multiple cysts (fluid-filled sacs). The affected kidney is devoid of renal architecture and filled with numerous irregular cysts resembling a cluster of grapes. The kidneys become non-functional as a result of deteriorated kidney tissues. It is usually unilateral, but in a few cases, it may show bilateral presentation.
What Is the Epidemiology of Multicystic Dysplastic Kidney?
The incidence is found to be one in 4000 live births. It is reported to be more common in males than females. More often occurs on the left side kidney as compared to the right kidney, and the majority of MCDKs are unilateral.
How Is Multicystic Dysplastic Kidney Classified?
It is classified into two types:
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Simple Multicystic Dysplastic Kidney - It is defined as unilateral dysplasia with normal contralateral kidney with compensatory hypertrophy and no associated genitourinary anomalies detected by ultrasound or physical examination.
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Complex Multicystic Dysplastic Kidney - It is defined as the bilateral dysplasia or abnormalities of the contralateral kidney or genitourinary tract detected by ultrasound or physical examination.
What Is the Etiology of Multicystic Dysplastic Kidney?
The exact etiology is unclear. Most cases of MCDK are sporadic, and few cases showing familial links have been reported in the literature. Gene mutations such as SIX1 (SIX Homeobox1) and PAX2 (paired box gene 2) are reported, but they need further evidence.
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Few studies report the aberrant genetic expression during the embryogenesis of the kidney resulting in improper coordination between the ureteric bud and the metanephric mesenchyme leading to the formation of non-functional nephrons and poorly formed collecting ducts.
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Another hypothesis is that it is caused due to the blockage of urine flow from its path of drainage from the kidney during the early stages of development, leading to the formation of the dysplastic kidney with multiple cysts.
What Is the Pathophysiology of Multicystic Dysplastic Kidney?
The embryogenesis of the kidney happens during the fourth week of intrauterine life. The ureteric bud integrates and branches into the metanephros leading to the development of functional nephrons and collecting ducts. The failure of the ureteric bud to integrate and branch into the metanephros would probably result in the formation of the non-functional dysplastic kidney with the formation of multiple irregular cysts.
Potter’s Syndrome Associated With Multicystic Dysplastic Kidney
Patients with bilateral MCDKs produce low urine as a result of non-functional kidneys; this, in turn, reduces the amniotic fluid required for the survival of the fetus in the intrauterine environment. As a consequence of this, Potter’s syndrome develops, which is characterized by the atypical physical appearance of the baby, such as cranial anomalies, clubbed feet, pulmonary hypoplasia, etc.
What Are the Conditions Associated With Multicystic Dysplastic Kidney?
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Wilms Tumor - This is a common kidney cancer affecting children. Studies report that patients with MCDK have a 0.03 to 0.1 % risk of developing Wilms tumor.
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Chronic Renal Failure - Studies report that patients with complex MCDK are more prone to develop chronic renal failure. The risk is found to be 29 % in seven years.
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Vesicoureteral Reflux - It is the backward flow of urine from the bladder into the ureters or even to the kidneys. Studies show that patients with MCDK are at high risk of developing vesicoureteral reflux.
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Renal Cell Carcinoma - Few studies suggest that patients with MCDK are at risk for renal cell carcinoma in their older age.
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Anomalies of Internal Genitalia - Studies report that 15 % of patients with MCDK show associated anomalies of the internal genitalia.
What Are the Symptoms of Multicystic Dysplastic Kidney?
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The unilateral MCDKs are usually asymptomatic as the contralateral kidney functions normally except for the presence of an abdominal mass in children. Few may show the problems of frequent urinary tract infections and hypertension at the later stages.
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Bilateral cases are characterized by the signs of Potter's syndrome, and most of the time, the children do not survive due to the non-functional kidneys and associated complications.
How Is Multicystic Dysplastic Kidney Diagnosed?
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Antenatal Diagnosis
MCDKs are usually diagnosed in a routine ultrasound around 20 weeks of gestation. In the case of unilateral MCDKs, the affected kidney appears smaller, improperly developed with multiple cysts of varying size, and the absence of normal renal parenchyma and the renal sinus echoes. In the case of bilateral MCDKs, both the kidneys are affected and improperly developed with considerably reduced amniotic fluid.
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Renal Ultrasound
Post-natal ultrasonographic appearance would demonstrate the presence of multiple non-communicating cysts resembling a cluster of grapes. Studies report that by two years of age, almost 60 % of kidneys shrink, and 20 % will become undetectable in ultrasound examination. The contralateral kidney may show compensatory hypertrophy.
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Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) Scans
CT and MRI scans would demonstrate a much more detailed report of the above-said findings.
How Is Multicystic Dysplastic Kidney Managed?
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The unilateral MCDKs generally need no treatment as the other kidney is performing renal functions, and the affected kidneys usually shrink and do not cause any problems.
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Nephrectomy should be considered when the MCDK increases in size instead of shrinkage; it should be surgically removed to prevent further complications.
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Children affected with bilateral MCDKs have a very less chance of survival; they usually die a few days after birth or, most of the time, show stillbirth.
Follow-Up Needed in Patients With Multicystic Dysplastic Kidney:
Long-term follow-up is not required in children with unilateral MCDK; renal ultrasound is recommended at an interval of three months till the first year of life and every six months till two to five years. Blood pressure should be monitored.
What Is the Prognosis of Multicystic Dysplastic Kidney?
The prognosis of the unilateral multicystic dysplastic kidney is good as there is a spare kidney functioning properly. The careful monitoring of the functioning kidney is mandatory to check for the development of associated complications affecting its function. The bilateral MCDKs show poor prognosis as it is a fatal condition, with most fetuses undergoing abortion as a consequence of low amniotic fluid.
Conclusion:
The multicystic dysplastic kidney is a severe form of renal dysplasia and is described as a developmental malformation characterized by the formation of non-functional kidney mass with numerous irregular cysts. The unilateral MCDKs usually do not need any treatment, but the associated complications need close monitoring and treatment. Bilateral MCDKs are rare and fatal.
