Urinary tract dilation (UTD) risk stratification system

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  A is for antenatal in UTD classification system

  
  
  
  
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    A1 = low risk for postnatal uropathy

    
    
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    A2-3 = increased risk for postnatal uropathy

  
  
  
  
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  P1, P2, and P3 for postnatal findings

Measure anterior-posterior renal pelvis diameter (AP RPD)

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  Best technique is with spine at 12 or 6 o’clock

Normal AP RPD

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  < 4 mm from 16-27 wk and < 7 mm when ≥ 28 wk

UTD A1 = isolated mild renal pelvis distention

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  AP RPD 4-7 mm at 16-27 wk; 7-10 mm when ≥ 28 wk

  
  
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  Associations: Aneuploidy, early obstruction/reflux

  
  
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  Follow-up at 32 wk to look for resolution or progression

UTD A2-3 criteria (need only 1 to make diagnosis)

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  AP RPD > 7 mm at 16-27 wk; >10 mm when ≥ 28 wk

  
  
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  Dilated calyces regardless of AP RPD

  
  
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  Dilated ureter or abnormal bladder

  
  
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  Echogenic kidney (> liver or spleen)

  
  
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  Thin renal parenchyma

  
  
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  Oligohydramnios from genitourinary cause

UTD A2-3 cases are more likely to progress

Look carefully at morphology of genitourinary tract distention to best determine level of obstruction

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  Most common cause of upper tract obstruction is ureteropelvic junction obstruction

  
  
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  Most common cause of lower tract obstruction is posterior urethral valves (in male fetuses)

Obtain image with kidney + liver/spleen

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  Consider cystic dysplasia if renal echogenicity > liver/spleen echogenicity

  
  
  
  
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    From postobstructive or primary cystic dysplasia

  
  
  
  
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  Look for small cortical cysts in all UTD cases