Callosal Dysgenesis

KEY FACTS

Terminology

• Partial or complete absence of corpus callosum (CC), hippocampal commissure, or anterior commissure (AC); can be isolated or associated with additional cerebral malformations

• Spectrum of congenital CC structural abnormalities

  • Total agenesis (absence from birth of all anatomically defined regions of CC)

  • Partial agenesis (absence from birth of at least 1, but not all, regions of CC)

  • Hypoplasia (thinner CC with normal anteroposterior extent)

  • Hyperplasia (thick CC resulting from decreased postnatal axonal pruning)

  • Dysgenesis (CC present but malformed in some way, including partial AC and hypoplasia of CC)

Imaging

• Absent corpus callosum on sagittal, coronal views

• Atrium/occipital horns often dilated (colpocephaly)

• DTI: Callosal fiber tracts form Probst bundles instead of crossing, where corpus callosum is absent

• Vertical/posterior course of anterior cerebral artery

Pathology

• Most common feature seen in CNS malformations (> 130 syndromes)

• May be complete or variably partial

• May have interhemispheric dysplasia: Meningeal cysts, lipomas

Clinical Issues

• Any age; classically identified in early childhood, most common malformation found in fetuses

• Seizures, developmental delay, cranial deformity/hypertelorism

• Sporadic/isolated agenesis/dysgenesis corpus callosum: Normal/near normal at 3 years (75%), but subtle cognitive defects apparent with increasing complexity of school tasks

• Agenesis/dysgenesis CC with associated/syndromic anomalies = worst

Diagnostic Checklist

• Look for absent/incomplete CC rather than indirect signs

• Fully assess for associated lesions

TERMINOLOGY

IMAGING