Macrocephaly

• Initial evaluation of fetal macrocephaly involves differentiating among:
  • Hydrocephalus
  • Space-occupying lesions
  • Megalencephaly
• Diagnosis typically achieved by fetal ultrasound.
• Family history of macrocephaly with normal outcomes suggests dominant familial macrocephaly.
• Primary megalencephaly:
  • Results from abnormalities in neuronal proliferation, migration, and organization.
  • May be associated with syndromes such as Sotos syndrome and Neurofibromatosis (discussed elsewhere).

Hemimegalencephaly

• Defined as unilateral hamartomatous overgrowth of a cerebral hemisphere.
• Characterized by:
  • Disturbances of proliferation, migration, and differentiation.
  • Abnormal gyral patterns including pachygyria or polymicrogyria.
  • Ventriculomegaly or ventricular asymmetry (common initial fetal diagnosis).
  • Thickened, unlaminated cerebral cortex with:
    • Loss of cellular alignment
    • Presence of heterotopias
    • Giant balloon cells
• Potential involvement of cerebrum and cerebellum.
• Prognosis:
  • Poor outcome generally anticipated.
  • Common complications include:
    • Severe intellectual disability
    • Hemiparesis
    • Early-onset intractable epilepsy