Definition: Genitourinary tract obstruction (at any level) causing renal parenchymal destruction

Progression: Urinary tract dilation (UTD) → ↑ renal echogenicity → small peripheral cortical cysts → large cysts

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  Findings are variable depending on stage of progression

Compare kidney echogenicity with liver echogenicity

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  Normal kidney echogenicity ≤ liver echogenicity

  
  
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  Abnormal kidney echogenicity > liver echogenicity

  
  
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  Cortical cysts are always abnormal finding

Variable appearance of UTD

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  Depends on level and age of obstruction

Variable amniotic fluid volume (unilateral vs. bilateral)

Most common causes of obstructive renal dysplasia (ORD)

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  Severe ureteropelvic junction obstruction

  
  
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  Posterior urethral valves in male fetus

Multicystic dysplastic kidney

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  Can look exactly like late ORD

Non-ORD

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  Echogenic kidneys without UTD

Autosomal recessive polycystic kidney disease

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  Large echogenic kidneys is key finding

  
  
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  Without UTD and without visible cysts

Look carefully for small cortical cysts in kidneys with significant hydronephrosis

Look for unilateral loss of corticomedullary differentiation (CMD) as early finding

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  Note that CMD is not always seen in fetus

Measure contralateral kidney to see evidence for compensatory hypertrophy

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  Contralateral kidney compensates for abnormal kidney and is considered “super kidney”