Multicystic dysplastic kidney (MCDK): Renal cystic dysplasia

Multiple noncommunicating cysts in kidney

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  Intervening renal tissue is sparse and abnormal

  
  
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  Large kidney size in 90%

  
  
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  Often lose normal kidney reniform shape

Bilateral MCDK in 20%

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  Severe oligohydramnios or anhydramnios

  
  
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  Grim prognosis from pulmonary hypoplasia

Contralateral renal anomaly (non-MCDK) in 1/3

MCDK pelvic kidney can mimic dilated bowel/pelvic mass

MCDK can be partial (upper or lower pole only)

Other nonrenal anomalies in 5%

Role of surveillance

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  Evaluate contralateral kidney and amniotic fluid

  
  
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  MCDK can enlarge dramatically (↑ hydrops risk)

Obstructive cystic dysplasia

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  Early hydronephrosis → late renal parenchymal cysts

  
  
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  Can look identical to MCDK in late phase

Ureteropelvic junction obstruction

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  Dilated calyces mimic cysts

MCDK most often does not function

MCDK tends to grow in fetal life and then involute

Contralateral renal evaluation is essential

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  Large contralateral kidney suggests compensatory hypertrophy and is good prognosticator

  
  
  
  
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    Measure renal length and look up in published tables

  
  
  
  
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  Look carefully for hydronephrosis, cysts, ↑ renal echogenicity

Clue to pelvic MCDK is lack of normal kidney in flank