Polydactyly

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  1 or more extra digits or parts of digits

  
  
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  May be preaxial (thumb side) or postaxial (pinky side)

  
  
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  Nonsyndromal: May be isolated or familial

  
  
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  Syndromal: Common feature in multiple syndromes

  
  
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  Diabetes increases risk of preaxial polydactyly

  
  
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  Important feature of trisomy 13

Syndactyly

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  Fusion of 1 or more digits; very easy to miss

  
  
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  Can be isolated but more often part of syndrome

  
  
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  Syndromic case may be extensive (mitten syndactyly)

  
  
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  Triploidy has characteristic fusion of 3rd and 4th digits

Clenched hand

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  Trisomy 18; look for overriding 2nd finger

  
  
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  Feature of neuromuscular disorders (e.g., arthrogryposis)

Clinodactyly

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  Radial deviation of distal 5th finger

  
  
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  2-4% of normal fetuses have clinodactyly

  
  
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  Minor marker for trisomy 21

Split hand/foot malformation (ectrodactyly)

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  Lobster claw deformity: Old term that should no longer be used

  
  
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  Deep median cleft with missing central phalanges and metacarpals/metatarsals with fusion of remaining digits

  
  
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  Creates deep cleft in midhand/foot

  
  
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  May involve only 1 or both hands/feet

Easy to both under and over diagnose

Use 3D ultrasound to aid in diagnosis

Feet are also affected in many of these conditions but are harder to evaluate

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  Be suspicious of polydactyly when foot appears too wide

Seldom isolated abnormality; carefully scan for other findings that would point to specific syndrome