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Multicystic dysplastic kidney disease (MCDK) is one of the most common renal abnormalities that can be identified during fetal ultrasound evaluation. It occurs in approximately 1 in 4300 live births.
Frequently, MCDK is unilateral and isolated with overall favorable outcomes. However, when it occurs bilaterally or with other anomalies, the prognosis may be considerably worse.
Bilateral MCDK occurs less frequently, with a reported incidence of 1 in 10,000. It is frequently found in male fetuses.
Definition
Multicystic dysplastic kidneys are defined by echogenic renal parenchyma with multiple noncommunicating cysts of variable sizes with no evidence of obstructive nephropathy.
The commonly identified ultrasonographic appearance of MCDK is a cystic paraspinal mass with cysts of various sizes distributed along the periphery of the kidney that do not communicate with each other.
When unilateral MCDK is present, a normal fluid-filled bladder should be present, and the level of amniotic fluid should also be normal. Absence of a fluid-filled bladder or decreased amniotic fluid should prompt an evaluation for an anomaly in the contralateral kidney, which will affect outcomes (Figure). A contralateral renal anomaly is present in approximately 40% to 50% of cases.
Multicystic dysplastic kidney demonstrating a typical appearance of echogenic renal parenchyma with multiple noncommunicating cysts of variable sizes (between calipers).
Society for Maternal-Fetal Medicine. SMFM Fetal Anomalies Consult Series #4. Am J Obstet Gynecol 2021.
MCDK is isolated in approximately 70% to 75% of cases. Many cases include associated anomalies of the genitourinary tract, including contralateral renal agenesis, which occurs in approximately 15% of cases.
Other genitourinary abnormalities observed in the contralateral kidney include urinary tract obstruction and vesicoureteral reflux; abnormalities of the genitalia can also be present.
Extrarenal malformations can be seen in approximately 25% of cases. These may include cardiac, central nervous system, and, gastrointestinal anomalies; omphalocele; and vertebral and skeletal malformations.
Obstructive renal dysplasia due to ongoing severe urinary tract obstruction may cause cystic dysplasia with cysts of various sizes and an appearance similar to MCDK, but these cysts tend to develop over time and are noted in the late second and third trimesters of pregnancy. Autosomal recessive kidney disease results in enlarged hyperechoic kidneys with small uniform cysts, and with this disorder, the renal cortex is often spared and can appear hypoechoic. Many other genetic syndromes are characterized by cystic renal disease with cysts present in the medulla or glomeruli of the kidney. The appearance of these cysts may differ from those seen in MCDK, in which cysts occur throughout the kidney and the kidney parenchyma is also dysplastic.
Genetic Evaluation
Chromosomal abnormalities and syndromes are present in approximately 7% to 14% of pregnancies with suspected MCDK.
The chance of an underlying chromosomal or genetic etiology increases with the presence of extrarenal anomalies.
Diagnostic testing (chorionic villus sampling or amniocentesis) with chromosomal microarray analysis (CMA) should be offered when MCDK is detected. Xi et al
found that when CMA was performed in cases of isolated MCDK, a pathogenic copy number variant was identified in 14% of cases. In cases of nonisolated MCDK, specific molecular testing may be indicated depending on the syndrome being considered. Although cystic kidneys may occur as an isolated abnormality, a detailed ultrasound examination to identify associated anomalies may inform further prenatal testing.
If there are additional anomalies, consanguinity, or a family history of a specific condition, gene panel testing or exome sequencing is sometimes useful because CMA does not detect single-gene (Mendelian) disorders. If exome sequencing is pursued, appropriate pretest and posttest genetic counseling by a provider experienced in the complexities of genomic sequencing is recommended. After appropriate counseling, cell-free DNA screening is an option for patients who decline diagnostic evaluation, particularly if a common aneuploidy is suspected.
Pregnancy and Delivery Management
Follow-up ultrasonography is recommended at 32 weeks of gestation to evaluate the contralateral kidney, fetal growth, and amniotic fluid volume. Fetal echocardiography should be considered given the association of MCDK with other anomalies. Consultation with pediatric nephrology and urology specialists may be considered, particularly when there is concern for an anomaly in the contralateral kidney. Insufficient evidence exists regarding any potential benefit of antenatal testing, and timing and mode of delivery should be based on usual obstetrical indications.
Prognosis
Unilateral isolated MCDK with a normal contralateral kidney is associated with an excellent prognosis. Aslam and colleagues
reported outcomes in a cohort of children with isolated unilateral MCDK diagnosed prenatally and found that there was complete involution of MCDKs by 10 years in more than 50% of those affected. There was no hypertension, malignancy, or significant proteinuria noted long term. Surgical removal is indicated when the affected kidney is enlarging or if the mass effect from the MCDK impacts respiration or feeding in the neonate.
In contrast, bilateral MCDK results in severe impairment of renal function that will result in oligohydramnios or anhydramnios. Early-onset anhydramnios and oligohydramnios will result in varying degrees of pulmonary hypoplasia and significant morbidity and mortality. The combination of both renal failure and pulmonary hypoplasia is lethal. Postnatal evaluation by both pediatric nephrology and urology specialists is recommended as ongoing surveillance may be needed.
Summary
MCDK is one of the most commonly seen genitourinary abnormalities that can be noted in midgestation. Prognosis is dependent on whether the lesion is unilateral or bilateral, and the presence of associated abnormalities in the contralateral kidney or extrarenal abnormalities impact outcomes. The presence of extrarenal findings raises concern for a possible genetic etiology. Isolated unilateral MCDK has an excellent prognosis both in utero and postnatally. Most cases resolve over time without the need for surgical intervention.
References
Scala C.
McDonnell S.
Murphy F.
et al.
Diagnostic accuracy of midtrimester antenatal ultrasound for multicystic dysplastic kidneys.
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