CNS development

Question 1

What is the pathogenesis of holoprosencephaly?

Answer 1

Failure of the hemispheres to separate

Question 2

What is the difference between Chiari I, II and III?

Answer 2

Chiari I - abnormally formed cerebellar tonsils causes tonsilar herniation

Chiari II - tonsilar herniation due to spinal cord tethering or a myelomeningocele. Will lead to an obstructive hydrocephalus

Chiari III - tonsilar herniation due to failure of the posterior fossa to grow or a cervical/occipital encephalocele

Question 3

What is the pathogenesis of Dandy-Walker syndrome?

Answer 3

Hypoplasia/agenesis of the cerebellar vermis (the region of the cerebellum that divides the two hemispheres) resulting in the 4th ventricle becoming a large cavity and the foramen of Luschka and Magendie failing to open and hydrocephalus.

Question 4

What is syringomyelia?

Answer 4

When CSF in the central canal of the spinal cord dissects into the surrounding white matter to form a cyst or cavity.

Question 5

What is the pathogenesis of lissencephaly? What are its clinical manifestations?

Answer 5

Lissencephaly is due to disordered neuronal migration, either arrested migration (classical) or over migration (cobblestone)

Classical lissencephaly is characterized by a “smooth brain” on imaging due to few sulci/gyri

Cobblestone lissencephaly is characterized by an excessive number of sulci/gyri