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Multicystic Dysplastic Kidney
Introduction
Multicystic dysplastic kidney (MCDK) is a form of severe renal dysplasia that typically results in a nonfunctioning kidney. The parenchyma is replaced by numerous cysts of varying size, with echogenic intervening tissue and an atretic ureter. Microscopically, undifferentiated epithelium and primitive ducts are surrounded by fibromuscular connective tissue. Bilateral MCDK usually results in Potter sequence (see Chapter 10 ), with early and severe oligohydramnios conferring an extremely poor prognosis secondary to pulmonary hypoplasia along with renal failure. When MCDK is unilateral, contralateral renal anomalies, in particular vesicoureteral reflux (VUR), may complicate the prognosis. The phenotypic presentation is variable, with some kidneys massively enlarged and others hypoplastic; over the course of gestation, the dysplastic kidney may enlarge, become smaller, or regress completely. Prenatal ultrasound (US) is useful for identification of this renal anomaly and, if unilateral, for surveillance of kidney size and detection of any associated abnormalities.
Disorder
Definition
MCDK is a form of severe renal dysplasia in which the kidney contains numerous smooth-walled cysts of varying size that do not communicate with a renal pelvis, surrounded by an echogenic cortex. The ureter is atretic, and the kidney is generally nonfunctioning.
Prevalence and Epidemiology
In prenatal series, the prevalence of unilateral MCDK is about 1 : 4000 births, with a reported range of 1 : 2000 to 1 : 7000. The variation likely reflects the difficulty identifying dysplastic kidneys that are small or contain few cysts. Bilateral MCDK accounts for 25% of cases, a prevalence of about 1 : 12,000 births. There is a slight male predominance for unilateral MCDK—60% of cases occur in males. When the disease is unilateral, the left kidney is more commonly affected. Bilateral MCDK is more common in females.
Unilateral MCDK is associated with contralateral renal anomalies in 30% to 40% of cases, which may have important prognostic implications because the contralateral kidney is often the only functioning kidney. The most common contralateral renal abnormality is VUR in 20% of cases, followed by ureteropelvic junction (UPJ) obstruction in 12% of cases (see Chapter 12 ). Nonrenal anomalies have also been reported in 25% of cases, including cardiac anomalies (particularly ventricular septal defects), central nervous system anomalies, spinal malformations, and gastrointestinal obstructions. Cystic dysplasia may also occur as a component of numerous syndromes, including Meckel-Gruber syndrome and Kallmann syndrome. When MCDK is found in the setting of other abnormalities, the aneuploidy risk is as high as 25%. As an isolated anomaly, unilateral MCDK is not strongly associated with aneuploidy; however, recent series have described an increased risk for pathogenic copy number variants using chromosomal microarray analysis.
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