Congenital Anomalies of Posterior Fossa

Cerebellar vermis ± hemispheres may be hypo- / dysplastic.

Predominant involvement of cerebellar hemispheres is characteristic of pontocerebellar hypoplasia + disruptive cerebellar development in very premature newborns.

Posterior fossa malformations typically involve both cerebellar hemispheres equally.

Hypoplasia ± dysplasia of one cerebellar hemisphere is likely due to prenatal hemorrhage.

1. PREDOMINANTLY CEREBELLUM
   1. predominantly vermian involvement
      1. Dandy-Walker malformation
      2. Blake pouch cyst
      3. Megacisterna magna
      4. Arachnoid cyst
      5. Isolated vermian hypoplasia
      6. Rhombencephalosynapsis
   2. global cerebellar cortical maldevelopment
      1. Lissencephaly
      2. Polymicrogyria
      3. Periventricular nodular heterotopia
      4. Primary microcephaly
      5. Congenital CMV infection
   3. unilateral cerebellar involvement
      1. PHACES syndrome
      2. Cerebellar cleft
2. CEREBELLUM + BRAINSTEM
   1. Pontocerebellar hypoplasia
   2. Joubert syndrome
3. PREDOMINANTLY BRAINSTEM
   1. Pontine tegmental cap dysplasia
4. PREDOMINANTLY MIDBRAIN
   1. Dysplasia of diencephalomesencephalic junction