CNS Abnormalities

Forebrain

• Anencephaly
  • failure of anterior neuropore to close resulting in failure of brain and calvarium to form
  • no swallowing center → polyhydramnios
  • ↑ AFP 
    • most common cause of  ↑ AFP is incorrect pregnancy dating 
• Holoprosencephaly
  • failure of prosencephalon to divide and form cerebral hemispheres
  • represents a field defect with regional manifestations including  
    • absence of olfactory bulbs and tracts
    • cyclopia, cleft palate, cleft lip
  • associated with
    • Patau syndrome (trisomy 13) and Edwards syndrome (trisomy 18)
    • severe fetal alcohol syndrome
    • cleft lip/palate
• fetal alcohol syndrome

Posterior Fossa

• Dandy-Walker syndrome 
  • dilation of 4th ventricle
  • absence of cerebellar vermis
  • small cerebellar hemispheres
  • posterior fossa cysts
  • enlargement of posterior fossa
  • associated with hydrocephalus and spina bifida
• Arnold Chiari I 
  • cerebellar tonsil herniation through foramen magnum
  • often presents in adulthood with chronic headaches and ataxia
  • associated with cervico-thoracic syringomyelia 
  • milder in severity in comparison to type II malformations 
• Arnold Chiari II 
  • due to small posterior fossa, the cerebellar tonsils herniate through foramen magnum causing aqueductal stenosis and hydrocephaly 
  • may present with synringomelia, thoracolumbar spina bifida with myelomeningocele
  • symptoms present from compression of medulla oblongata and CN IX, X, and XI
    • reduced gag reflex
    • vocal cord paralysis
    • laryngeal stridor
    • swallowing difficulty
• spastic dysphonia

Spinal Cord

• Syringomyelia 
  • central canal of spinal cord enlarges
  • nerves closest to central canal affected first
    • spinothalamic tract: bilateral loss of pain and temperature sensation in affected area, touch not affected
      • occurs most often at C8-T1
      • cape-like pattern loss 
• often associated with Chiari I, less frequently with Chiari II