• 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
      • 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

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