Complete absence of corpus callosum (CC)

May be partially present but abnormal (dysgenesis)

Mild ventriculomegaly often 1st clue

Absent cavum septi pellucidi (CSP)

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  CSP: Anechoic, box-shaped midline structure between frontal horns of lateral ventricles

  
  
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  Do not mistake paired fornices for CSP

Axial plane

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  Absent CSP, teardrop-shaped ventricles (colpocephaly) , parallel lateral ventricles

  
  
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  May see associated interhemispheric cyst or lipoma

Coronal plane

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  Absent CSP, Texas longhorn morphology to anterior horns of lateral ventricles, nonvisualization of CC

Midline sagittal plane

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  Absent or abnormal CC

  
  
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  Radial, spoke-wheel, sunray appearance of medial gyri radiating to 3rd ventricle

  
  
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  Abnormal vertical course and branching of anterior cerebral artery

  
  
  
  
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    Normally pericallosal branch parallel to CC, callosomarginal parallel to cingulate gyrus

  
  

Mild ventriculomegaly: Ventricles have normal shape

Scan in all 3 planes in any fetus with absent CSP

Look at shape of ventricles: Colpocephaly strongly associated with callosal abnormalities

Look for AVID complex

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  A symmetric v entriculomegaly, i nterhemispheric cyst, d ysgenesis of CC

ACC seldom isolated; look for other anomalies in brain (50%) and body (60%)