Table 1.

Structural changes within the posterior fossa in Chiari II malformation

Small posterior fossa

Small cerebellar volume (especially the cerebellar hemispheres)

Reduced cerebellar weight

Dysplastic looking cerebellum

Expanded midsagittal vermis area

Vermis (± tonsils) herniation below foramen magnum

Upward herniation of the superior vermis

Wrapping of the cerebellar hemispheres around the brainstem

Enlarged tentorium incisura

Dysplastic tentorium cerebelli with abnormally low insertion

Inferior displacement of the lower brainstem

Tectal beaking

Medullary-cervical kink

Aqueduct stenosis

Small and inferiorly displaced fourth ventricle

Enlarged foramen magnum